LE HUY BA Chu bien

(Tai ban lan th ba, co chnh ly va bo sung)

NHA XUAT BAN AI HOC QUOC GIA TP HO CH MINH - 2008

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LI NHA XUAT BAN

Giao s Tien s khoa hoc Le Huy Ba la mot trong nhng nha moi trng hoc au tien cua Viet Nam c ao tao bai ban, tot nghiep Tien sy Khoa hoc ve oc chat moi trng nc ngoai va la nha khoa hoc co nhieu kinh nghiem. Trong nhng nam qua, va tham gia cong tac giang day nganh Moi trng cac trng ai hoc, cho he ai hoc, he cao hoc va hng dan luan an tien s trong nc va day ngoai nc, va trc tiep nghien cu ong thi lam cong tac thc tien ket hp vi viec hoc tap nhng kinh nghiem cua nc ngoai, Giao s Tien s khoa hoc Le Huy Ba a nghien cu, bien soan nhieu cong trnh ve moi trng va sinh thai hoc nh: Moi trng hoc c ban, Sinh thai moi trng hoc c ban, Sinh thai moi trng at, Quan tr moi trng c ban, Moi trng kh hau thay oi - moi hiem hoa cua toan cau, Tai nguyen moi trng va s phat trien ben vng, Kinh te moi trng hoc, Sinh thai moi trng ng dung, Nhng van e at phen Nam Bo, Ly thuyet va kinh nghiem thc tien ISO/4001, Quan tr moi trng trong nong lam ng nghiep, Du lch sinh thai Cac cong trnh nay hau het a c xuat ban, kp thi phuc vu nhu cau hoc tap, nghien cu cho nganh Moi trng, ong thi gop phan nang cao nhan thc ve van e moi trng nc ta.

Cuon sach oc hoc moi trng c ban la cong trnh tiep theo cua Giao s Le Huy Ba cung cac cong s. ay la mot cuon sach c bien soan cong phu, e cap en nhieu van e ve oc chat, oc to. Moi loai oc chat, oc to eu c phan tch ro ve nguon goc, tnh chat va bien phap phong chong. Sach cung a ra nhieu dan chng minh hoa cu the.

oc hoc moi trng c ban la cuon sach ve oc chat hoc moi trng au tien c bien soan va xuat ban Viet Nam. Nhieu khai niem mi ve oc chat, oc to c gii thieu trong cong trnh nay.

Nha xuat ban ai hoc Quoc gia Thanh pho Ho Ch Minh tran trong gii thieu cuon oc hoc moi trng c ban vi ban oc.

NHA XUAT BAN AI HOC QUOC GIA

TP HO CH MINH

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CHNG 1

TONG QUAN VE OC HOC MOI TRNG (ECOTOXICOLOGY, AN OVERVIEW)

1.1. GII THIEU Trong nhng thap nien gan ay, con ngi a quan tam en tac

ong o nhiem moi trng oi vi sc khoe cong ong, bi v ngoai s lay lan cac benh truyen nhiem (dch ta, thng han) do vi sinh vat gay ra, nhng benh nguy hiem nh ung th, AIDS, quai thai, cac d tat bam sinh tre do cac chat oc hai trong moi trng a xuat hien va ngay cang gia tang nhieu ni tren the gii.

Xa hoi cang phat trien, cong nghiep hoa cang nhanh th ty le chat thai oc hai t san xuat cong nghiep va nhng anh hng bat li t cac hoat ong cua con ngi tac ong vao moi trng cang tang nhanh. Cac chat oc hai con sinh ra do ro r t qua trnh san xuat, van chuyen va lu tr cac chat oc. Ngay ca nc r, tham thau t bai rac cung gay nguy hiem cho khu dan c xung quanh. Cac loai o nhiem hoa hoc sinh ra t qua trnh san xuat cong nghiep va khai thac qua mc tai nguyen thien nhien ang ngay cang lam nguy hai cho sinh quyen. Cac tac ong ay khong nhng anh hng en loai ngi ma ca cac sinh vat song tren trai at.

S phat xa, cac kh thai, chat thai dang vo c, hu c, bui gia tang ang e doa moi trng va sc khoe con ngi. Them vao o, s thai ra ngay cang nhieu cac kim loai oc, cac chat hu c co tnh oc va o ben cao, sau o ton lu, tch luy trong chuoi thc an va gay hai nghiem trong en con ngi va cac ong vat hoang da. anh gia bien co (risk assessment) va quan ly bien co (risk management) t cac nguy c tiem tang la rat can thiet e bao ve cac the he tng lai.

Chu trnh tng tac gia chat o nhiem va c the sinh vat la qua trnh tiep xuc, gay nen tac ong sinh hoc, the hien qua s hap thu, phan bo trong c the, chuyen hoa, tng tac vi cac thanh phan sinh hoa nhay cam, t o co the gay nhng bien oi ve sinh hoa trong c the, dan en benh tat.

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e nghien cu tat ca cac tac ong neu tren oi vi con ngi, ca

the sinh vat va cac quan xa sinh vat trong he sinh thai, chung ta se tiep can mot mon khoa hoc mi, o la mon oc hoc moi trng (environmental toxicology) hay con goi la oc hoc sinh thai (ecotoxicology). No la mot bo mon cua nganh oc chat hoc (toxicology) nhng lai nam trong nganh Moi trng hoc (environmental sciences).

Can phan biet hai khai niem: oc chat hoc va oc hoc moi trng. a) oc chat hoc J.F. Borzelleca nh ngha: "oc chat hoc la nganh hoc nghien cu ve

lng va chat cac tac ong bat li cua cac tac chat hoa hoc, vat ly, sinh hoc len he thong sinh hoc cua sinh vat song". oc chat hoc la nganh khoa hoc ve chat oc. No la mot nganh khoa hoc c ban va khoa hoc ng dung.

b) oc hoc moi trng Hai khai niem oc hoc moi trng (environmental toxicology) va oc

hoc sinh thai (ecotoxicology) trong moi trng hoc c xem la ong nhat. o la nganh khoa hoc chuyen nghien cu cac tac ong gay hai cua oc chat, oc to trong moi trng oi vi cac sinh vat song va con ngi, ac biet la tac ong len cac quan the va cong ong trong he sinh thai. Cac tac ong bao gom: nguon goc phat sinh, con ng xam nhap cua cac tac nhan hoa, ly va cac phan ng gia chung vi moi trng (Butler, 1978).

oc hoc moi trng nghien cu s bien oi, ton lu va tac ong cua tac nhan gay o nhiem von co trong thien nhien va cac tac nhan nhan tao a anh hng en cac hoat ong song cua sinh vat trong he sinh thai, cac tac ong co hai en cho con ngi. Nh vay, khac vi oc chat y hoc hay Hoa oc hoc, oc hoc moi trng co oi tng nghien cu khong ch la con ngi ma ca cac loai sinh vat, quan the va quan xa. Phng phap nghien cu oc hoc moi trng th nghiem s tac ong va tch luy oc

Chat o nhiem, chat oc

Chuyen hoa

Tac ong

C the sinh vat

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chat, oc to tren nhng sinh vat song ch khong nghien cu rieng re thanh phan cua oc chat trong phong th nghiem.

Cac nghien cu ve oc hoc moi trng rat phc tap v co lien quan en nhieu loai oc to, lieu lng, nong o anh hng khac nhau, tac ong en nhieu loai khac nhau. Thi gian tien hanh anh gia mc o anh hng cua chat oc tren mot quan xa sinh vat kha dai. oi tng th nghiem thng tien hanh tren cac loai co c a, sinh ly gan giong nh con ngi. Sau o, dung phng phap ngoai suy nhng ket qua tm c e ap dung cho con ngi. Tuy nhien, cac nha sinh thai moi trng hoc cung th nghiem mot vai trng hp tren con ngi nh vi trung sot ret, mot vai loai ky sinh trung... e tm ra thuoc cha tr.

Muc tieu cua oc hoc moi trng la phat hien cac tac chat (hoa hoc, vat ly, sinh hoc) co nguy c gay oc e co the d oan, anh gia cac s co va co bien phap ngan nga nhng tac hai oi vi cac quan the t nhien (bao gom ca con ngi) trong he sinh thai. Cac th nghiem vat ly, hoa hoc, sinh hoc cung vi th nghiem oc chat moi trng a c phoi hp thc hien e d toan cac anh hng xau cua oc chat co the xay ra trong moi trng.

e hieu ro hn ve nganh khoa hoc mi me nay, chung ta can nam vng cac khai niem, moi quan he gia cac thanh phan trong he sinh thai va nhng ieu kien e ac tnh hoa hoc cua mot chat tr thanh oc tnh oi vi sinh vat va con ngi.

1.2. MOT SO KHAI NIEM C BAN (xem them phan Glossary cuoi sach tr 546-570)

oc hoc moi trng (environmental toxicology) va oc hoc sinh thai (ecotoxicology) la hai khai niem gan giong nhau. o la mon hoc nghien cu cac oc tnh cua cac tac nhan gay oc nh mot oc to, oc chat t chat gay o nhiem trong qua trnh o nhiem moi trng. oi tng gay oc lai chnh la tren con ngi va sinh vat va he sinh thai.

Tac nhan gay oc (toxic factor) la bat ky mot chat nao gay nen nhng hieu ng xau cho sc khoe hoac gay chet. Hau het cac chat eu co oc tnh tiem tang, ch co o ln cua lieu lng (hay nong o) hien dien cua chat o trong moi trng mi quyet nh no co gay oc hay khong (Paracelsus, 1538).

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Lieu lng oc (dose) la mot n v bieu hien o ln s xuat hien cac tac nhan hoa hoc, vat ly hay sinh hoc. Lieu lng co the c dien ta qua n v khoi lng hay the tch tren mot trong lng c the (mg, g, ml/kg trong lng c the) hay n v khoi lng hay the tch tren mot n v dien tch be mat c the (mg, g, ml/m2 be mat c the). Nong o trong khong kh co the c the hien qua n v khoi lng hay the tch tren phan trieu the tch khong kh (ppm) hay miligam, gam tren m3 khong kh. Nong o trong nc co the dien ta qua n v ppm hay ppb.

o oc cap tnh la o oc tnh thng c xac nh bang nong o cua mot hoa chat, mot tac nhan gay oc tac ong len mot nhom sinh vat th nghiem trong thi gian ngo oc ngan, trong ieu kien co kiem soat. e anh gia oc tnh cap va ngng oc, ngi ta dung cac ai lng sau e anh gia:

LD50 (median lethal dose): lieu lng gay chet 50% ong vat th nghiem, n v mg/kg ong vat song tren can.

LC50 (median lethal concentration): nong o gay chet 50% ong vat th nghiem, n v mg/l dung dch hoa chat; thng dung e anh gia oc tnh cua chat oc dang long hoa tan trong nc song, suoi hay nong o hi hoac bui trong moi trng khong kh o nhiem co the gay chet 50% so ong vat th nghiem.

To chc Y te the gii (WHO) a da vao gia tr LD50 e phan loai oc tnh cua oc chat. Gia tr LD50 cua mot chat cang nho, oc tnh cua chat o cang cao.

Co nhieu qui c phan loai cac chat oc da vao LD50 cua chung nh sau:

Nhom I : rat oc, LD50 < 100 mg/kg.

Nhom II : oc cao, LD50 = 100 - 300 mg/kg.

Nhom III : oc va, LD50 = 300 - 1000 mg/kg.

Nhom IV : oc t, LD50 > 1000 mg/kg.

Trong moi trng nc, oc tnh cua hoa chat oi vi thuy sinh c anh gia bi LC50. Gia tr nay cang thap, oc tnh cang cao.

Neu giai oan cuoi th nghiem khong gay chet ong vat th nghiem ma cac nong o (lieu lng) th nghiem dan en cac tac ong

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khac nhau oi vi 50% vat th nghiem th goi la lieu anh hng 50% ED50 (median effective dose) hay nong o anh hng 50% EC50 (Rand va Petrocelli, 1985).

Gia tr EC50 hay LD50 thng c thc hien trong vong 24 en 96 gi va c th nghiem tren mot loai chat nhat nh. V du nh th nghiem tren nguon nc ao ho, thuoc bao ve thc vat, mot loai chat ien hnh trong nc thai cong nghiep... e xac nh nong o va ngng an toan. Thi gian cung thng c ghi cung vi lieu lng gay chet: LD50 48 h hay EC50 24 h.

Mot phng phap nghien cu khac la o thi gian can thiet e xac nh 50% sinh vat th nghiem co phan ng ac biet (v du nh chet). Phng phap nay oi hoi phai gi mc o cua cac tac ong chon loc luon khong oi va theo doi trong thi gian th nghiem e xac nh thi iem 50% vat th nghiem chet, hay 50% vat th nghiem song sot. Thi gian o goi la median lethal time LT50 thi gian chet 50%.

Do t vong la mot yeu to de xac nh trong cac phan hoi nen th nghiem o oc cap tnh thong thng nhat la th nghiem nong o gay chet cap tnh; trong o, 50% phan hoi la thong so ch ve ham lng oc to c s dung va 96 h (hay t hn) la thi gian ngo oc tieu chuan (do no la thi gian can cho s ngo oc gay chet cap tnh). Thong so dung cho o oc cap tnh thng c s dung nhat cho ca va cac ong vat khong xng ln la 96 h LC50. Tuy nhien, do t vong khong de xac nh cho cac sinh vat khong xng, mot thong so khac, EC50 (nong o anh hng trung bnh), thng c s dung hn la LC50. Anh hng c s dung e c tnh EC50 cho mot so ong vat khong xng song (chang han daphnia, au trung ruoi nhue) la s bat ong, c xac nh la khong di chuyen. Cac tac ong thng c s dung e c tnh EC50 cho cua, tom bien, tom ong la s bat ong va mat can bang, c xac nh la mat kha nang duy tr t the bnh thng.

oc to cap tnh e xac nh o oc cap tnh, mot phng phap th nghiem thong

dung la xay dng mot th nghiem ma mot ket qua xac nh (ngha la, mot phan hoi toan phan hay khong: chet hay khong) c suy luan ra. Moi quan he gia nong o chat th va phan tram ca the b ngo oc c xac nh va mot ng cong nong o gay chet se c xac lap. Ket qua cua

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cac th nghiem ngan han cho thay (1) phan tram ca the sinh vat b giet hay bat ong trong moi nong o th, va (2) LC50 hay EC50 c ghi nhan t quan sat, tnh toan hay noi suy.

Bang 1.1: LC50 cua mot so hoa chat oi vi ca tue Hoa chat LC50

Triethylene glycol (TEG) 92,500mg/l

Dimethyl formanide (DMF) 10,410mg/l

Acetone 9,100mg/l

Dimethyl sulfoxide 33,500mg/l

(Nguon: US EPA, 1979)

o oc cap tnh tnh theo Micro (TM test) e xac nh o oc cap tnh, ngi ta con dung phng phap th

goi la TM test (Microtox Test) model 500 Analyser, Protocol for Basic Text (Microbix, 1992).

Nguyen ly phng phap th la kiem soat qua trnh trao oi chat cua vi sinh vat phat quang thi gian ngan 5 15 phut qua o, anh gia o oc cap tnh cua moi trng nc hay at, bun kh. Nhiet o c duy tr 15 27oC. Thiet b o la may Microtox model 500, o cng o phat quang cua vi sinh vat Vibrio fischeri NRRL B-11177, thuoc th Microtox Reagent. May th c noi vi mot may tnh cai at san phan mem Microtox data collection and reduction software version 6.0 hoac phan mem Microtox OmiTM. Trong ieu kien moi trng cha co hoac t oc chat, vi sinh vat phat quang manh do qua trnh ho hap te bao cua chung. Neu moi trng b nhiem oc, chat oc cang tang th lng phat quang cang giam. Ngi ta a ra mot ch so EC50 cng o phat sang cua vi sinh vat trong khoang thi gian 5 phut (hoac 15 phut) vi nhiet o t = 15 0,5oC. Tr so EC50 c oc qua may tnh.

o oc cap tnh tnh theo loai giap xac Ceriodaphnia Trong moi trng nc ngot co loai phieu sinh vat giap xac

Ceriodaphria, thng la thc an cho ca nho. Ngi ta s dung tnh nhay cam cua no vi nong o oc chat vi so lng ca the chet e xac nh mc o nhiem oc cua moi trng sau 24 gi, 48 gi.

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So lng ca the chet cua no cung c bieu dien qua EC50 24h EC50 48h hoac LC50 24h va n v tnh o oc ay la mg/l.

n v oc chat (TU Toxicity Units): la ai lng the hien lng oc chat cua mau th vi sinh vat th nghiem. Mot n v tnh tng ng vi mau pha loang giet chet 50% so lng sinh vat th nghiem.

TU = %)50(EC

(%)100

50

TU cang cao, EC50 cang thap th moi trng cang oc hai. Toc o phat thai oc chat (Toxicity Emission Rate) la lng oc

chat, oc to thai ra moi trng xung quanh trong thi gian mot ngay TER = TU/ngay = TU x Q (m3/ngay) He so phat thai oc chat (Toxicity Emission Factor TEF): la

lng oc chat phat thai tnh tren mot tan chat thai ran cac bai rac thai.

TEF = TU/tan rac ang phan huy = )ngay/ractan(H

TER

o oc man tnh Mot cong cu quan trong e hieu ro va anh gia kha nang gay oc

cua hoa chat oi vi sinh vat la o oc man tnh hay o oc toan vong i. o oc man tnh co the cho thay cac nong o cua hoa chat co the anh hng en qua trnh phat trien bnh thng va kha nang sinh san cua mot ca the sinh vat. Noi chung, nong o gay ra ngo oc man tnh thng thap hn nong o ngo oc cap tnh. Do o, o oc man tnh cung cap nhieu so lieu nhay cam hn o oc cap tnh.

Trong cac th nghiem e tm ra o oc man tnh, nong o ngng gay ra cac tac ong co hai ang ke thng c goi la nong o gay oc cc ai co the chap nhan c (MATC). MATC la mot nong o ly thuyet nam tren nong o cao nhat khong gay ra anh hng (NOEC) va nam di nong o gay oc thap nhat (LOEC), do o NOEC < MATC < LOEC.

Trong viec thiet lap moi quan he gia o oc cap tnh va o oc man tnh, mot thong so a c a ra s dung, o la yeu to ap dung (AF), la mot thong so khong th nguyen, thuan tuy hoa hoc, c tnh bang nong o ngng cua o oc man tnh chia cho nong o gay oc cap tnh. Yeu to ap dung AF c xem nh la dai nong o. Chang han, neu

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0,5 < MATC < 1,0mg/l va LC50 la 10 mg/l, va AF = MATC / LC50 0,5 < 1,0 / 10 = 0,05 0,1

Theo ly thuyet, AF kha on nh cho mot hoa chat. Do o, khi AF cua mot hoa chat a c xac nh cho mot loai thuy sinh vat nao o th no cung co the ap dung cho mot loai khac. Ly thuyet nay a cung cap mot c tnh ve nong o oc man tnh cua mot hoa chat len cac loai khong the tham gia cac phep th trong ieu kien gay oc man tnh do cha co u thong tin ve cac yeu cau can thiet e duy tr i song sinh vat. Ngoai ra, trong mot so trng hp, AF cung cung cap c tnh ve nong o oc man tnh ma khong can tien hanh th nghiem, mac du loai sinh vat co the tham gia. ieu nay a giup giam chi ph va thi gian s dung cho cac th nghiem. Cac nha nghien cu co the xac nh AF cua mot hoa chat oi vi mot sinh vat va sau o ap dung cho mot sinh vat khac. Chang han, AF cua mot hoa chat oi vi ca la t 0,05 - 0,1, AF nay co the ap dung e xac nh MATC cua mot loai giap xac nh tom, khi biet LC50 cua no la 1,0mg/l. MATC cua hoa chat nay oi vi tom se la:

MATC = AF x LC50 = 0,05 0,1 x 1,0 mg/l 0,05 < 0,1 mg/l Cuoi cung, mot s so sanh ve cac nong o hoa chat gay ra cac anh

hng co hai ang ke trong nghien cu o oc man tnh vi nong o hoa chat co the co trong moi trng nc (EEC) cho phep mot s anh gia ve cac kha nang ngo oc tiem tang ma hoa chat gay ra cho cac sinh vat nc.

oc tnh ban cap la tac dung gay hai c the ong vat neu hang ngay hoa chat c a vao c the trong khoang thi gian di 10% thi gian song cua ong vat th nghiem.

Mc khong thay c hieu ng thuoc (no observable effect level NOEL) la lieu lng toi a cua mot chat oc khong tao ra c mot hieu ng thay ro ret cac ong vat th nghiem. NOEL thng c dung lam hng dan e lap ra cac mc tiep xuc toi a ngi va thiet lap cac mc d lng chap nhan c tren cac loai nong san. Thong thng, mc tiep xuc va mc d lng chap nhan c c qui nh khoang 100 - 1000 lan nho hn NOEL e co c s an toan can thiet.

Phan hoi (response) la nhng phan ng cua mot c quan hay mot phan cua c quan noi tang (v du nh c bap) oi vi mot tac nhan kch thch (duffus). Tac nhan kch thch co the co mot vai dang, tac dung kch

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thch cang ln th phan hoi cang manh. Khi tac nhan kch thch la hoa chat, phan hoi lien he tng quan vi lieu lng (dose).

1.3. NHIEM BAN - O NHIEM CHAT OC VA NGO OC 1.3.1. O nhiem moi trng (pollution) (*) Chung ta biet rang cac hien tng ngo oc ngi va sinh vat eu

lien quan en lng oc to, oc chat co trong moi trng, ma oc chat nay lai xuat phat t chat gay o nhiem co trong moi trng b o nhiem.

nh ngha: O nhiem moi trng la hien tng suy giam chat lng moi trng qua mot gii han cho phep, i ngc lai vi muc ch s dung moi trng, anh hng en sc khoe con ngi va sinh vat. O nhiem moi trng vt qua mc nhat nh se la hien tng nhiem oc va ngo oc sinh vat va con ngi.

To chc Y te the gii nh ngha o nhiem la viec chuyen cac chat thai hoac nang lng vao moi trng en mc co kha nang gay hai cho sc khoe con ngi va s phat trien sinh vat hoac lam giam chat lng moi trng song.

Nguon gay o nhiem la nguon thai ra cac chat o nhiem. Chung ta co the phan chia cac chat gay o nhiem theo tnh chat hoat ong, nguon goc phat sinh, theo khoang cach khong gian nguon gay o nhiem chnh cung la nguon gay oc.

Chat o nhiem la cac hoa chat, tac nhan vat ly, sinh hoc nong o hoac mc o nhat nh, tac ong xau en chat lng moi trng. Khi o nhiem vt qua mc, chat o nhiem cung chnh la chat oc.

1.3.1.1. O nhiem, gay oc moi trng nc Nc la mot nguon tai nguyen ln trong thien nhien nhng do s

phan bo khong eu va do tac ong cua con ngi nen mot so ni tren the gii nc tr nen khan hiem hoac kem chat lng, khong s dung c. Do tnh de lan truyen nen pham vi cua vung o nhiem nc lan nhanh trong thuy vc va theo a phat trien cua san xuat cong nghiep, toc o o th hoa... Nhieu ni tren the gii hien nay ang b e doa thieu nc sach tram trong do tnh trang nguon nc b o nhiem hoac sa mac

(*)Xem Moi trng, tap I, Le Huy Ba, Nxb Khoa hoc va k thuat, 1997).

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hoa. Hau qua cua viec nhiem oc oc chat, oc to trong vung nc b o nhiem a, ang va se con phai giai quyet lau dai. Nc o nhiem la con ng de dang nhat a oc chat vao cac c the song va con ngi thong qua cac mat xch trong chuoi thc an, nc uong. V the, van e o nhiem nc va anh hng cua cac tac nhan oc trong nc en quan xa thuy sinh va con ngi can c quan tam nghien cu.

1.3.1.2. O nhiem, gay oc moi trng khong kh Khong kh la hon hp cac chat co dang kh, co thanh phan the tch

hau nh khong oi. Thanh phan cua khong kh kho la 78% N2, 20,95% O2, 0,93% Ar, 0,03% CO2, 0,002% Ne, 0,005% He. Ngoai ra, khong kh con cha mot lng hi nc nhat nh. Nong o bao hoa hi nc trong khong kh phu thuoc rat nhieu vao nhiet o.

O nhiem khong kh la s phong thch vao kh quyen cac loai kh, bui, hi hay cac hat khong phai la thanh phan khong kh kho, lam cho thanh phan khong kh thay oi, gay anh hng bat li cho con ngi, sinh vat va cac cong trnh.

Khong kh o nhiem cha rat nhieu loai chat oc nguy hai cho sc khoe con ngi va he sinh thai. Cac chat nay cang nguy hiem hn khi de dang xam nhap vao c the qua ng ho hap va da, hap thu vao mau hoac tac ong ngay len he than kinh.

1.3.1.3. O nhiem, gay oc moi trng at O nhiem nc, o nhiem khong kh co lien quan mat thiet en o

nhiem gay oc at ai. O nhiem at phan anh nhng phng thc canh tac phan ve sinh va nhng chnh sach sai lam ve quan ly, s dung at ai. O nhiem at phan anh s lien thong gia o nhiem nc, khong kh dan en o nhiem va gay oc cho at.

cac nc phat trien cung nh cac nc ang phat trien, o nhiem gay oc at con la do:

+ S dung qua mc trong nong nghiep nhng san pham hoa hoc nh phan bon, chat ieu hoa sinh trng, thuoc bao ve thc vat...

+ Thai vao at mot lng ln chat thai cong nghiep, chat thai oc hai.

+ Do tran dau

+ Do cac nguon phong xa t nhien va nhan tao.

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1.3.2. Nhiem ban (contamination) la trng hp cac chat la lam thay oi thanh phan vi lng, hoa hoc, sinh hoc cua moi trng nhng cha lam thay oi tnh chat va chat lng cua cac moi trng thanh phan. Nh vay, moi trng nc khi b o nhiem a trai qua giai oan nhiem ban, nhng mot moi trng nhiem ban cha chac a b o nhiem. Ngoai ra cung can biet them rang thuat ng Contamination ch thng dung cho o nhiem gay oc moi trng at va bun ay, khong hoac t dung cho moi trng khong kh, nc

1.3.3. Chat oc (toxicant, poison, toxic element) Chat oc la nhng chat gay nen hien tng ngo oc cho con ngi,

thc vat, ong vat.

Cac tac nhan gay o nhiem co mat trong moi trng en mot nong o nao o th tr nen oc. Nh vay, t tac nhan o nhiem, cac tac chat nay tr thanh tac nhan oc, chat oc va gay oc cho sinh vat va con ngi.

Trong moi trng thng co ba loai chat oc:

Chat oc ban chat (chat oc t nhien): gom cac chat ma du lieu lng rat nho cung gay oc cho c the sinh vat. V du nh H2S, Pb , Hg, Be, St, CO...

Chat oc khong ban chat: t than khong la chat oc nhng co luc no cung co the gay nen cac hieu ng oc khi vao moi trng.

Chat oc theo lieu lng: la nhng chat mc o bnh thng (hay mc o nen) cha bieu hien tnh oc; no ch co tnh oc khi ham lng tang cao trong moi trng t nhien. Tham ch mot so chat khi ham lng thap la chat dinh dng can thiet cho sinh vat va con ngi (Microelement hay Microfertilize), nhng khi nong o tang cao, vt qua mot ngng an toan nhat nh oi vi mot sinh vat nhat nh th chung tr nen oc. V du, trong moi trng at, NH+4 trong dung dch at la chat dinh dng cua thc vat va sinh vat khi nong o thap; nhng khi vt qua ty le 1/500 ve trong lng no se gay oc. Tng t, Zn la nguyen to vi lng can thiet e nang cao chat lng san pham nong nghiep nhng khi vt qua 0,78% a gay oc; hay Fe2+ vt qua nong o 500ppm la gay chet lua, vt qua 0,3 ppm trong nc la anh en sc khoe cua con ngi.

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1.4. CAC NGUYEN LY VE OC HOC MOI TRNG 1.4.1. Tnh oc Tnh oc cua mot chat oc phu thuoc vao cac yeu to sau:

ac tnh cua chat o oi vi sinh vat nhat nh V du : Pb, Hg, CuSO4, gay oc vi sinh vat.

Hg vo c t oc hn so vi Hg hu c. Chat hu c cha Cl co oc tnh cang cao khi so nguyen t Cl trong

phan t chat o cang nhieu: CH3Cl < CH2Cl2 < CHCl3 < CCl4. Hp chat amine, nitro cua benzene cang oc khi goc NH2 va NO2

cang nhieu trong phan t. Cac chat de tan trong nc thng de gay oc hn Nong o (hay lieu lng) cua chat oc: Nong o va lieu

lng cang tang tnh oc cang tang. Tac ong tong hp cua nhieu chat: neu nhieu chat oc cung

tac dung ong thi th mc o nguy hiem cang tang. Trong trng hp nay, nong o cac chat phai nho hn nong o cho phep cua tng chat. Cach tnh nong o cho phep:

1...TC

TC

TC

3

3

2

2

1

1

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Tr so ngng th hang (threshold limit value - TLV): oi vi mot hoa chat, TLV la nong o cua hoa chat (tnh theo ppm) khong tao ra nhng anh hng xau cho sinh vat trong mot khoang thi gian nao o. TLV thong dung nhat - thng ap dung cho nong dan - la nong o cua hoa chat ma nong dan phai chu ng trong 8 gi moi ngay va trong 5 ngay lien tiep. oi khi phai ap dung nhng tr so TLV ngan han cho nong dan v cong viec phai i vao vung x ly thuoc.

1.4.3. Tnh ben vng cua oc chat trong moi trng Nhieu chat hoa hoc co thi gian ban phan huy (half life) rat dai hay

rat kho b oxy hoa hoac kho b phan huy sinh hoc; do o, chung rat ben trong t nhien. V du, dioxin co thi gian ban huy t 10 -12 nam. Chung c thai ra moi trng tr thanh chat thai oc hai co i song rat lau dai va gay nguy hiem cho he sinh thai. Chung co the c hap thu vao cac c quan cua thc vat, ong vat rat lau ma khong b phan ra hay ao thai. Theo thi gian, chung co the c tch luy ngay cang nhieu qua moi bac dinh dng trong thap dinh dng, trc khi xam nhap vao c the con ngi. Nong o tch luy nay khi vt qua ngng oc gii han se gay nhng benh nguy hiem hoac lam thay oi cau truc te bao, ot bien gen gay ung th... lam suy thoai cac the he sau.

V du, s kien nhiem oc methyl thuy ngan vnh Minamata, Nhat Ban (1932 - 1971) khong ch oi vi ca ma ca he sinh thai trong nc va tram tch ay vnh, la mot ien hnh cho s ton tai ben vng cua oc chat trong t nhien. Hau qua la ng dan trong vung sau nhieu nam an ca b nhiem oc, a phat sinh nhng can benh la ma ch co Minamata. Ngay nay, sau nhieu co gang nao vet tram tch methyl thuy ngan va cai tao moi trng, ngi ta c tnh d lng con lai cua thuy ngan trong bun ay vnh phai en nam 2011 mi phan huy het.

1.5. MOT VAI LOAI OC CHAT IEN HNH (Se trnh bay ky hn cac chng sau)

1.5.1. Chat thai t cong nghiep dc pham Cong nghiep dc pham tao ra mot khoi lng ln cac chat thai

hoa hoc. Thanh phan cua cac chat nay lien quan en b mat cua san pham hay oc quyen sang che, do o kho cong khai hoan toan. Cac chat

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hoa hoc nay co the la chat c che sinh hoc hay chat oc oi vi qui trnh x ly va se gay nhieu van e cho moi trng song khi thai ra ngoai.

1.5.2. Thuoc tr sau hu c Tren th trng mot so loai thuoc bao ve thc vat a c s dung

nh DDT, lindane, chlordane, dieldrin, aldrin va heptachlor. Ve mat cong dung, chung c xem la co tac dung diet tuyet oi nhieu loai con trung khac nhau. Nhng khi cac loai tren c dung di dang dung dch, chung co kha nang dnh chat vao cac hat keo at, kho b ra troi theo dong nc va kho b phan huy sinh hoc hay hoa hoc trong moi trng t nhien. Thi gian ban huy cua chung tng oi dai (1-10 nam). Do khong tan trong nc nen chung co the c tch luy trong cac mo m va chuyen t ong vat sang con ngi qua thc an hoac qua nc uong khong kh o nhiem. Hien nay mot so hoa chat bao ve thc vat a b cam nh DDT nhng mot so ni van con dung va ton d trong at van con cao (Le Huy Ba, 2004).

1.5.3. Hp chat phenol Hp chat phenol xuat phat t goc benzene gom: polyphenol,

chlorophenol, phenoxy acid. Phenol khong mau, tinh the trang co the chuyen sang o khi b phi ra anh nang, tan tng oi nhieu trong nc. Phenol la phu pham cua cong nghiep hoa dau, t mo than, luyen coc hoac co the phan tch t nha ng, ieu che t tong hp hu c Phenol la nguyen lieu tho cua nhieu nganh cong nghiep. Mot v du ien hnh gan ay la viec 21 cong nhan a b bong da, phai i cap cu, nhap vien va e lai thng tat do tiep xuc vi phenol trong khi nao vet kenh co nc a b nhiem phenol t phe thai vo hat ieu Bnh Chanh, Thanh pho Ho Ch Minh (1999).

1.5.4. Cac hp chat PCB (polychloro biphenyl) Giong nh thuoc tr sau hu c, PCB la hp chat rat ben vng trong

t nhien. Mot phng phap thng dung e pha huy cau truc cua PCB la nung 1200oC trong 2 phut. Con ng thong thng nhat e PCB xam nhap vao c the ngi la qua thc vat, thuy san, kh quyen (hat bay hi). Chung co the ton lu trong mo m cua cac sinh vat song.

1.5.5. Chat thai co goc halogen Xuat phat t qua trnh giat tay, lam sach kim loai, det nhuom hay

thuoc da. Goc halogen co the ket hp vi cac chat thai trong nc thai e

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tao thanh cac hp chat rat nguy hiem, oc hai, linh ong trong nc va ton tai lau ben trong t nhien.

1.5.6. Chat oc cyanur T hoa chat ai vang, tuyen quang, x ly hi nong trong luyen thep

va mot so chat thai cong nghiep.

1.5.7. Chat oc phong xa Co hai nguon chat thai phong xa ma pho bien nhat la t nha may

nang lng hat nhan: mo quang uranium; chat thai benh vien.

Co ba loai tia phong xa anh hng len con ngi la alpha, beta, va gamma. Mc o gay hai tuy thuoc loai tia. Chat phong xa se gay ra tnh trang thieu mau, suy nhc c the, met moi, rung toc, uc thuy tinh the, noi ban o da, ung th hoac gay nhng ot bien trong qua trnh hnh thanh te bao, bien oi gen, lam anh hng en ca mot the he tng lai.

1.5.8. Cac chat oc kim loai nang Kim loai nang co trong bun cong ranh, kenh rach o th, nc thai

cong nghiep nhat la luyen kim, xi ma qua con ng thc pham, tch luy trong c the sinh vat,... gay anh hng lau dai len c the sinh vat va con ngi, gay ung th.

1.6. CAC YEU TO LAM ANH HNG EN TNH OC CUA OC CHAT, OC TO Tien lieu nhng anh hng co hai cua chat oc oi vi con ngi

va cac quan the sinh vat trong he sinh thai la mot viec khong de. Tuoi tac, gii tnh, sc khoe va nhieu yeu to moi trng khac gop phan vao ket qua cuoi cung.

1.6.1. Lieu lng va thi gian tiep xuc vi hoa chat oc: noi chung, khi lieu lng tiep xuc cang cao va thi gian tiep xuc cang lau th tnh oc co tac hai cang ln.

S hien dien cung mot luc nhieu loai hoa chat trong c the song hoac trong moi trng tai cung mot thi iem tiep xuc cung la mot yeu to tac ong en tnh oc cua cac chat.

e chng to tac ong nay, cac nha oc chat hoc thng tien hanh cac th nghiem e xac nh LD50 (lieu gay chet 50% con vat th nghiem)

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cua moi loai oc chat, LD50 anh gia tnh oc tng oi cua mot chat. V du, mot chat co LD50 la 200mg/kg b.w (body weight) se co tnh oc bang mot na cua hoa chat co LD50 la 100mg/kg b.w.

1.6.2. Cac yeu to sinh hoc Tuoi tac: Nhng c the tre con, ang phat trien qua thi ky non yeu se

b tac ong cua chat oc manh hn nhng c the ngi ln. V du, tre em b nhiem oc ch va thuy ngan de dang va nghiem trong hn ngi ln v he than kinh cua chung cha hoan chnh rat nhay cam vi chat oc; con vat th nghiem nho b ngo oc cua SOx va NOx trong khong kh o nhiem nang hn con vat ln.

Tnh trang sc khoe: dinh dng kem, cang thang than kinh, an uong khong ieu o, benh tim, phoi va hut thuoc la gop phan lam suy yeu sc khoe va lam con ngi de b nhiem oc hn. Yeu to di truyen cung co the quyet nh s phan ng cua c the oi vi mot so chat oc.

Yeu to gen di truyen: cung co tac dung nhat nh en mc o tac hai va kha nang anh hng lau dai qua vai the he cua oc chat. Mot so gen nhat nh se de b tac ong cua mot so oc chat nhat nh.

1.6.3. Cac nhan to moi trng anh hng en hoat tnh cua oc chat

Cac nhan to o nhiem lan truyen trong cac moi trng thanh phan (moi trng nc, khong kh, at) co the gia tang tnh oc va cung co the ket tua, giam tnh oc. Cac tac nhan o nhiem chu anh hng manh cua cac yeu to cua moi trng thanh phan ma cac oi tng sinh vat va he sinh thai nam trong moi trng o. Co the ke mot so tac nhan anh hng nh sau :

pH moi trng: tnh kiem, acid hay trung tnh cua moi trng la yeu to au tien anh hng en tnh tan, o pha loang va hoat tnh cua tac chat gay oc. Mot tac nhan o nhiem ton tai trang thai hoa tan thng co oc tnh cao hn oi vi thuy sinh.

V du: pH acid, kem (Zn) co oc tnh cao hn v ton tai hnh thai Zn2+ va ZnHCO3+ (hoa tan); trong khi o pH kiem, kem co oc tnh thap do ton tai trang thai Zn(OH)2 (ket tua).

EC (o dan ien): co anh hng nhat la vi cac chat oc co tnh ien giai.

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Cac chat can trong moi trng nc, khong kh, at, gay ket dnh hay sa lang oc chat. V du, trong vung at chua phen, neu co cac hat keo set l lng, oc chat Al3+ la oc chat ien hnh trong he sinh thai at phen, se lien ket vi cac hat mang ien am nay va se tram lang xuong, lam giam oc tnh cua Al3+ trong dung dch.

Nhiet o: anh hng en kha nang hoa tan, lam gia tang toc o phan ng, tang hoat tnh cua cac chat o nhiem. V du, khi nhiet o cao, HgCl2 se tac dung nhanh gap 2 -3 lan so vi nhiet o thap. Thuoc tr sau DDT va mot so loai thuoc diet ray thng tang oc tnh khi nhiet o t 100C len 300C.

Dien tch mat thoang: anh hng trc tiep en s phan bo nong o va lieu lng, phan huy chat o nhiem, ac biet la chat hu c khong ben vng. Dong nc co be mat ln, dong chay manh, lu lng ln co kha nang t lam sach cao, giam oc tnh.

Cac chat oi khang hoac chat xuc tac: neu trong moi trng ton tai chat xuc tac th hoat tnh cua chat o nhiem se tang cao nhieu lan. Ngc lai, khi co chat oi khang th oc tnh se giam hoac triet tieu.

Cac yeu to ve kh tng, thuy van nh o am, toc o gio, anh sang, s lan truyen song, dong chay, o man cung gay tac ong kha ln en hoat tnh cua oc chat, nhat la tac ong en kha nang lan truyen oc chat trong moi trng.

Kha nang t lam sach cua moi trng: Moi mot he moi trng sinh thai eu co kha nang t lam sach cua no. Kha nang nay cang ln th tnh chu oc va giai oc (detoxification) cang cao.

1.7. DIEN BIEN VA CON NG I CUA OC CHAT Chat oc phat sinh t nhieu nguon (t nhien va nhan tao) va xam nhap

vao c the bang nhieu cach, sau mot thi gian tch luy se tang tnh hoat ong hoac phan huy, lam giam oc tnh va ao thai khoi c the. Sau ay la trnh t cac bc tren ng i cua oc chat khi tac dung len con ngi.

1.7.1. Nguon phat sinh A. Nguon thien nhien a) T hoat ong cua nui la: nui la phun nham thach nong, giau

sulfur, methane va cac chat kh khac cung vi tro va khoi bui gay o

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nhiem khong kh, sau o la gay oc tren mot khu vc rong ln, khong ch cua mot quoc gia ma anh hng en nhieu quoc gia lan can.

b) Chay rng (cung co the do nhan tao): lan truyen nhanh va rong; thai nhieu tan tro, khoi, bui gay oc tan pha nghiem trong he sinh thai khu vc. Chay rng tram U Minh la mot v du.

c) Phan giai yem kh cac hp chat phan tch hu c t nhien vung am lay, song rach, ao, ho: sinh ra nhieu chat o nhiem, chat oc (nh CH4, H2S, vi trung, vi khuan yem kh...) cho moi trng nc, at, khong kh trong va sau qua trnh phan giai.

B. Nguon nhan tao Rat a dang, do qua trnh phat trien san xuat, do nhu cau xa hoi

tang nhanh e thoa man nhu cau cua con ngi. Cac hoat ong co thai ra cac chat oc cho moi trng sinh thai bao gom:

a) Cong nghiep

Nganh nhiet ien: thai ra bui, khoi va hi nong, cac kh oc hai, san pham cua hoat ong ot nhien lieu hoa thach (nh SOx, CO, CO2, N2O, NO2).

Nganh vat lieu xay dng: bui, kh SO2, CO, CO2, N2O, NO2)...

Nganh hoa chat, phan bon: khoi thai lan bui hoa chat, co tnh an mon, nc thai acid (hoac kiem), trong nc thai lan nhieu chat l lng va d lng nhieu loai hoa chat gay hai cho he sinh thai nh toluene, cac dan xuat gay ung th...

Khai thac va che bien dau mo: sinh ra dau ro r, can dau, chat thai ran cua san xuat... Ta biet rang, dau mo va san pham chng cat dau eu gay oc cho sinh vat va he sinh thai.

Nganh det nhuom, giay, nha, chat tay ra: thai ra nhieu khoi bui, kh oc, nc thai oc hai, chat thai ran oc hai.

Nganh luyen kim, c kh: bui, cac kh giau SOx, NOx, CO, CO2, cac kim loai nang.

Nganh che bien thc pham: chu yeu nc thai ra co ham lng chat hu c cao, tao nen cac oc to trong moi trng.

Nganh giao thong van tai: chat thai do khoi xang, dau m, bui ch, bui at, tai nan, nhat la tai nan tran dau...

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Nguon o nhiem cong nghiep do hai qua trnh gay ra: ot nhien lieu va do boc hi, ro r tren day chuyen san xuat va tren cac ng ong dan. Qua trnh ot nhien lieu thai ra rat nhieu chat oc, qua ong khoi nha may, i thang vao khong kh.

cac nc cong nghiep phat trien, rat nhieu dien tch at rong ln c dung lam ni chon chat thai phong xa, chat thai hoa chat oc nguy hiem, chat thai sinh hoat. T ay phat sinh nhieu yeu to anh hng xau cho moi trng. My co khoang 76.000 bai rac cong nghiep c thieu ot; an Mach 3.200 bai, trong o co 500 bai rac hoa hoc. Nhat Ban co lng rac thai hang nam khoang 20 trieu tan.

Trong khoang chuc nam gan ay, viec chon chat thai phong xa, chat thai oc hai ngoai bien va ai dng ang gay o nhiem va nhiem oc nang cho mot so vung bien. ay la moi lo ln cho ngi va thuy sinh vat. Ngoai ra, hang nam bien va ai dng nhan trung bnh 1,6 trieu tan dau do tau thuyen thai xuong; khoang 1,1 trieu tan do cac tai nan tran dau.

b) Nong nghiep: do viec s dung thuoc bao ve thc vat nhom clo hu c (DDT, DDD, lindane, thiodane, heptachlor...) va cac hp chat polychlobiphenyl (PCB), dioxin... la cac chat kho tan trong nc nhng co kha nang hap thu va tch luy trong cac mo m.

c) Hoat ong du lch, sinh hoat, pha rng, chien tranh cung la cac nguyen nhan lam phat sinh cac nguon o nhiem. V du: hau qua cua viec rai chat oc khai quang, diet co cua My trong chien tranh Viet Nam con gay hai vai chuc nam sau.

1.7.2. Xam nhap: la qua trnh chat oc tham qua mang te bao va xam nhap vao mau. oc chat co the xam nhap vao c the con ngi va sinh vat thong qua ba ng:

Tieu hoa: o an, thc uong b nhiem ban, khong am bao qui tac an toan ve sinh thc pham nen oc chat de dang xam nhap vao c the va gay benh.

Mot so oc chat hap thu thong qua cac con vi khuan song trong da day. Chat co tnh kiem yeu th hap thu yeu hn trong c the khi no di chuyen xuong ruot non, ruot gia va ao thai ra ngoai.

Ch co mot so chat i ti nao, con lai, chu yeu oc chat i qua gan, than, qua sa me, tuyen mo hoi va tuyen sinh duc.

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Ho hap: khong kh c ht qua phoi co cha nhng chat o nhiem, chung ton tai khong ch dang kh ma con dang long, bui ran co kha nang bay hi nh cac loai dung moi, cac loai hoa chat, thuoc tr sau, lan hu c, thuy ngan. Mot vai chat co tnh thang hoa bien oi trc tiep t the ran sang kh nh naphthalene, paradichlorobenzene nhiet o cang cao, kha nang xam nhap qua ng ho hap cang ln. Cac chat oc sau khi c hap thu qua mang nhay se lan toa va i vao mau. Chung phan bo tuy theo oc to va cau truc phan t cua chung.

Cac chat oc dang ran hay long, l lng trong khong kh nh khoi, sng mu..., vi hat nho di 1 micron, co the vao phoi de dang va ti tan phe nang, gay ton thng nh phu phoi, benh bui phoi. Toan bo phe nang co dien tch rat ln vi mot mang li mao mach day ac giup chat oc khuech tan nhanh vao mau, khong qua gan va khong c giai oc nh theo ng tieu hoa, ma chung i thang vao tim, e ngay sau o, i en cac phu tang, ac biet en he than kinh trung ng. Do o, chat oc xam nhap qua ng ho hap tac ong gay oc nhanh gan nh la c tiem thang vao tnh mach.

Bui kh oc co kch thc phan t t 1 - 5 micron de dang i vao cac phe quan va phe nang. Con nhng hat ln hn 10 micron th b gi lai he thong ho hap ngoai (muoi)

e e phong nhiem oc qua ng ho hap, phai co qui nh nong o gii han cho phep cua oc chat trong moi trng khong kh va qui nh thi gian lam viec trong moi trng co nong o nhat nh cho ngi va sinh vat (xem them chng 4).

ng da: da co vai tro bao ve chong tac ong cua cac yeu to hoa hoc, vat ly va sinh hoc. Do mot so nguyen to nhay cam vi lp m di da nen co the i qua da, vao he tuan hoan chung cua c the.

Mot so hp chat co the i qua da nh xang pha ch hu c, nicotin, cac dan xuat nit va amin thm, cac dung moi co chlor, cac hp chat thuoc tr sau, lan hu c, chlor hu c...

Nhiem oc qua da cang de xay ra neu da b ton thng ve mat c hoc (chan thng), ly hoc (bong), cac chat hoa hoc (cac chat kch thch va an da, gay bong). Neu nhiem qua niem mac cang nguy hiem hn v niem mac co mat o mao mach day.

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Chat oc tham qua mang te bao va xam nhap vao mau, en cac c quan trong c the. Sau o, cac hoa chat co the b chuyen hoa. Mot so khac se tch luy vao cac c quan khac nhau. Kha nang ton lu hoa chat trong c the phu thuoc vao ac iem hoa hoc, cau truc phan t, tnh chat vat ly cua chung, phu thuoc lng hoa chat vao c the, thi gian tiep xuc, xam nhap. Ngoai ra, tnh oc hai con phu thuoc vao cau truc cua c quan tiep nhan nh: s hap thu, phan bo, chuyen hoa trong c the va kha nang bai tiet cua tng sinh vat. Cac hoa chat co tnh a m cao se de dang tap trung trong cac mo m nh: DDT, chlodane, PCB... protein cua plasma co the lien ket vi ong, kem, barbiturat; cac thuoc khang sinh va paraquat tch luy trong phoi; ch co kha nang tch luy trong xng.

Mot so te bao tren da tao thanh cac tuyen mo hoi, chiem tren hn 1% dien tch da, nhieu chat de b ao thai qua tuyen mo hoi; do vay, t oc to c hap thu qua da. Lp tren cung cua da goi la chat sng, phang, dep, co cha protein. Lp nay co dan, an hoi. Lp sng da nay coi nh la mot la chan, can tr cac oc to t ben ngoai vao. Hap thu dang nc qua da rat cham, nhng oc to co cha lipid se qua da nhanh hn. Ban chan, long ban tay hap thu oc chat cham hn so vi au va nach.

Tom lai, khi cac oc chat hoac chat la i vao c the thong qua mot hoac nhieu ng nh a ke tren, chung se i vao mau. Sau o, chung co the b ao thai ra khoi c the bang mot s chuyen hoa sang mot the khac hoac bai tiet qua gan, than (vi cac chat oc tan c trong nc) va qua phoi (vi cac chat oc co tnh bay hi cao). Cac chat oc khong bai tiet ra co the ton lu, tch luy trong cac mo, cac c quan noi tang roi gay cac benh nguy hiem nh ung th hoac gay cac ot bien ve gen va di truyen. Phan gay oc nay se c tiep tuc xet trong phan tiep theo.

1.7.3. Gay oc Khi chat oc i vao c the, se xay ra phan ng gia no va c the.

Phan ng o co the lam tang hay giam oc tnh cua chat oc, tuy thuoc vao nhieu yeu to nh :

- Ban chat, cau truc cua chat oc

- Lieu lng chat oc i vao c the e tao ra phan ng gia te bao va chat oc o; c tnh bang n v ppb hay ppm (mg/kg trong lng c the).

- Thi gian tac dung

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V du: tiep xuc vi NO2 trong vai gi, vi nong o 15-50 ppm, gay ton thng tim, phoi. Nhng cung vi nong o nay, tren cung mot oi tng, tiep xuc trong vai giay th gan nh khong co bieu hien ton thng.

- The trang sc khoe: an uong ay u chat dinh dng, c the co sc e khang vi oc chat.

- Tuoi tac: tuoi nhi ong va tuoi gia de nhay cam vi cac oc chat.

- Gii tnh.

V du: DDT khong oc vi chuot mi sinh nhng oc vi chuot ln. Parathion oc vi chuot mi sinh nhng khong oc vi chuot ln.

Chuot cong c b oc gap 10 lan so vi chuot cong cai.

Chat oc co tac ong khac nhau len c the song khac nhau. V du, methanol oc vi ngi nhng lai khong oc vi cho, meo, chuot. Do vay, chung ta phai chon oi tng nghien cu phu hp, cau truc sinh ly tng ng vi con ngi e t o co the dung phng phap ngoai suy.

Mot vai v du tac hai cua oc chat tren cac oi tng

* oi vi thc vat: thay ro trong tac dung lam giam nang suat cay trong hay giam nang suat sinh hoc, khi oc chat tang cao trong moi trng at, nc.

V du, SO2 lam han che s phat trien cua thc vat. Nong o SO2 t 3 ppm tr len se lam rung la cho en gay chet cay.

Nong o CO t 100 - 1000 ppm se lam xoan la, rung la, gay chet non cho nhieu loai cay trong.

O3 gay vang la, ngan re, giam san lng hat.

* oi vi tai san, cong trnh O3 lam cao su nt ne, tang tnh an mon cong trnh.

SO2 lam giam tuoi tho cua vai, nilon, t nhan tao.

NO2 lam phai mau thuoc nhuom, hong vai, t, nilon

CO2 va SO2 lam giam tuoi tho cong trnh.

Ngoai ra con co mot so chat (nh Pb) khong gay oc ngay ma tch tu ben trong c the, sau o di tac ong cua cac phan ng sinh hoa trong c the, no tr nen oc.

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Cac chat gay oc c chia thanh nam nhom:

Nhom 1: gay bong, kch thch da va niem mac. V du nhom acid, hi acid, kh NH3.

Nhom 2: kch thch ng ho hap, nh Cl, NOx, HCl...

Nhom 3: cac chat gay ngat nh CO, CO2, kh CH4, C2H6 .

Nhom 4: cac chat tac dung len he than kinh, nh hydrocarbon, sulfurhydro, cac loai ru.

Nhom 5: gay oc cho he thong c quan nh he tao mau, he tieu hoa.

1.7.4. Phan huy Mot so oc chat co the b thuy phan hoac chuyen hoa di tac dung

cua anh sang t ngoai (phan ng quang hoa), tao chat co oc tnh kem hn. V du, cac thuoc bao ve thc vat ho pyrethroid nh decis, sherpa...

Mot so loai thuoc bao ve thc vat co goc phot pho hu c de thuy phan nh parathion, methylparathion, DDVP... kho gi c nong o cao trong moi trng sau mot thi gian dai, nhat la khi moi trng nc co tnh kiem manh. Thi gian ban huy cua chung ch 10 - 15 gi trong ieu kien pH trung tnh. Do o, ngi ta a dung dung dch loang cua cac chat kiem nh dung dch xut, nc voi e x ly, tieu oc cac vat lieu b nhiem chat bao ve thc vat ho phot pho hu c va cac chat oc quan s co goc phot pho hu c nh sarin, soman, VX...

Nhieu chat hu c trong nc thai sinh hoat (chat beo, carbohydrate, hydrocarbon...) de dang b oxy hoa e cho cac san pham khong oc hoac t oc oi vi ong thc vat thuy sinh.

C4H10O3N + O2 Vi sinh CO2 + H2O + NH3 (C4H10O3N: cong thc chung cua chat o nhiem trong nc thai sinh hoat)

NH3 + H2O pH 7

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1.7.5. ao thai Than la c quan bai tiet chu yeu cac chat oc qua ng nc tieu.

Gan va mat co vai tro quan trong oi vi bai tiet DDT va Pb. Phoi la ni bai tiet cac kh oc. Ngoai ra, cac chat con c bai tiet qua mo hoi, nc mat, sa, nc tieu va phan.

Toc o ao thai chat oc khoi c the phu thuoc vao toc o chuyen hoa va bai tiet chung. Thong thng, trong c the, cac chat oc c chuyen hoa thanh chat t oc hn, co tnh a m kem hn, tnh hoa tan trong nc cao hn, do o de tham vao mang te bao va de b bai tiet. Qua trnh nay goi la kh hoat hoa sinh hoc hay kh oc (detoxification). Tuy nhien, mot so t chat khi i vao c the lai bien thanh cac chat oc hn. Qua trnh nay c goi la qua trnh hoat hoa sinh hoc hay la qua trnh tang o oc (incresing of toxicity). Viec tao ra chat chuyen hoa co oc tnh cao hoac thap hn chat ban au phu thuoc vao tnh chat, cau truc hoa hoc va kieu phan ng cua tac chat ban au.

Chat o nhiem

Chat oc

Kh hoat hoa sinh hoc De bai tiet

Giam oc tnh

c the (tang o phan cc, tang tnh a nc)

Hoat hoa sinh hoc Kho bai tiet

Tang oc tnh

(giam o phan cc, tang tnh a m)

S o 1a: Chuyen hoa va ao thai cua chat oc

1.8. PHAN LOAI OC CHAT, OC TO 1.8.1. C s phan loai Trong he sinh thai ton tai rat nhieu loai oc chat khac nhau, vi

nhng mc o tac ong tren moi loai oi tng cung khac nhau va con ng xam nhap, gay hai cua chung cung rat a dang... Do o, tuy theo

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muc ch nghien cu, oi tng nghien cu ma chung ta co c s e phan loai oc chat thch hp. Co rat nhieu c s phan loai oc chat, co the ke ra mot vai cach phan loai nh sau:

- Phan loai theo nong o - lieu lng - Phan loai theo ban chat - Phan loai theo moi trng (at, nc, khong kh, sinh quyen) - Phan loai theo mc o nguy hiem - Phan loai theo nguon goc oc chat - Phan loai theo dang ton tai - Phan loai thong qua ng xam nhap va gay hai - Phan loai theo nganh kinh te - xa hoi: oc chat trong nong

nghiep, cong nghiep, y te, quan s...

- Phan loai theo qui trnh cong nghe (dang nguyen lieu, dang phu gia, dang dung moi, dang chat thai...)

- Phan loai theo tac dung sinh hoc n thuan (tac dung kch ng, tac dung gay ngat, d ng, ung th, ot bien, quai thai...)

- Phan loai theo sinh hoc he thong: gay oc len mo than kinh, len c quan tao mau; gay oc len gan, than, cac c quan khac.

Tm hieu ky moi c s phan loai se cho chung ta co cai nhn khai quat ve oc chat, oc to trong moi trng song.

1.8.2. Phan loai theo nong o, lieu lng 1.8.2.1. Nong o nen: la nong o cua cac nguyen to san co trong

moi trng t nhien trong sach, tc la nong o hien dien cua chung khong gay anh hng xau ti sc khoe cua con ngi va sinh vat, khong lam giam chat lng cuoc song sinh vat trong cac moi trng thanh phan.

Hau het cac nguyen to hoa hoc eu hien dien vi mot nong o thch hp trong moi trng. Chung la cac nguyen to co ch gop phan tao nen va duy tr s s song tren trai at. Tuy nhien, mot so trong chung la cac chat oc tiem tang. Khi nong o - lieu lng co mat cua chung tang cao va vt qua mot gii han nhat nh (tuy theo moi oi tng b tac ong ma gii han nay cao hay thap), th cac oc chat tiem tang nay se phat huy oc tnh cua no len vat tiep xuc. Nh vay, mot chat khi nong

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o thap (nong o nen) co the la chat dinh dng, co ch cho i song cua con ngi va sinh vat, nhng khi nong o (lieu lng) co mat tang cao hay do kha nang tch tu sinh hoc, chung vt qua ngng nguy hiem va gay hai cho sinh vat va he sinh thai.

Can quan tam en moi trng co mat cua loai oc chat nong o - lieu lng nay. Neu ton tai trong at, a th nong o cho phep cao hn trong moi trng nc hay khong kh rat nhieu. Mot nong o tng oi nho trong nc co the gay oc nghiem trong cho he sinh thai thuy. Ngc lai, mot nong o tng oi ln trong at a, nhng do ton tai the ran nen tac hai oi vi sinh vat (c tnh la nong o tong cong cua nguyen to o) co the cha xay ra.

V du, cac nguyen to kim loai nang nh cadmium, thuy ngan, cobalt, ch... co the ton tai trong at a, khoang vat trong t nhien en nong o vai hoac vai chuc ppm van khong gay oc, nhng khi chung hoa tan trong nc th ch vi nong o nho hn 1 ppm a gay oc cho mot so loai ong, thc vat.

Lng oc chat san co trong at ch la mot phan nho cua tong so co trong lp phong hoa, khoang t hn 10%, thong thng la t hn 1%.

Tnh oc cua loai oc chat nong o - lieu lng thng lien quan en hai yeu to:

- Lieu lng chat oc - Tnh nhay cam sinh vat oi vi nhng chat oc ac biet ang c

nghien cu. Lieu lng do sinh vat tiep nhan b anh hng bi nong o chat oc

co trong moi trng va thi gian tiep xuc vi oc chat hoac a oc chat vao c the. Do vay, mot oc chat co nong o nho trong nen moi trng trong mot thi gian dai cung van co the se gay oc cho cac oi tng trong he sinh thai do kha nang c tch luy sinh hoc. Neu chu tac ong thng xuyen cua dang nhiem oc nay (oc man tnh), con ngi va sinh vat co kha nang b anh hng en he thong di truyen, dan en ot bien, ung th hoac anh hng en phoi thai.

1.8.2.2. Nong o cho phep cua chat oc nh ngha Nong o cho phep la ch tieu ve nong o dung e khong che chat

oc trong viec bao ve sc khoe cho ngi va sinh vat. No la c s giam sat

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moi trng, anh gia tiep xuc nghe nghiep va tac hai sc khoe cung nh co y ngha d phong.

- Theo To chc Y te The gii, nong o toi a cho phep la nhng nong o chat oc ma nong o o, ngi cong nhan tiep xuc 8 gi/ ngay va 40 gi/tuan ma no khong gay anh hng g cho sc khoe cua ho.

- Lien Xo (cu), nong o toi a cho phep la nhng nong o cua mot oc chat nhat nh, khong anh hng g en sc khoe cong nhan trong thi gian ho ang lam viec va ca sau nay, suot i ho.

- Cac gia tr gii han ngng cua My qui nh ch ap dung cho a so cong nhan co sc khoe bnh thng, khong ke nhng ngoai le. Qui nh nay ch co tnh chat ch dan ve ve sinh moi trng ma thoi!

Ten goi - Lien Xo (cu) goi la nong o toi a cho phep, viet theo ch La tinh

la PDK (predelno dopustima koncentraciia).

- My thng dung tr so gii han ngng (TLVs - threshold limit values), ten theo Hoi cac nha ve sinh cong nghiep My dung.

- Vien tieu chuan My co dung ten nong o toi a cho phep MAC (maxima allowable concentration).

- c dung ten nong o toi a cho phep. - Phap co nhieu ten goi khac nhau nhng cung mot y ngha. V du

nh concentratien maximale admissible (NTCP), limites tolerables, limites permissibles, seuils limites...

- Viet Nam dung ten nong o toi a cho phep (NTCP) trong cac van ban cua Bo Y te, thng ten ngan la NCP.

Qui nh NCP Moi quoc gia co qui nh rieng NCP cua nc mnh tuy theo quan

iem va tnh hnh cua moi nc.

- Viet Nam: qui nh trong van ban "Nhng tieu chuan tam thi ve ve sinh" - Bo Y te.

- WHO: la chon theo quy nh cua My va Lien Xo (cu) 24 chat oc ma NCP cua hai nc nay xap x nhau va khuyen cao nen ap dung tren pham vi quoc te.

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- Cac tr so NCP cua My thng cao hn Lien Xo 1-90 lan. - Lien Xo la nc co qui nh NCP sm nhat, sau o la My, c

(trc 1945). Cac nc khac thng la ke tha qui nh NCP cua My (de hn). Mot vai nc ap dung cua Lien Xo (nghiem ngat hn) hoac mot so nc ieu chnh cho hp vi nc mnh.

- Ngoai nhng NCP trong 8 gi, 40 gi lao ong, Lien Xo va My con qui nh NCP co cac tr so cao hn nhng vi thi gian tiep xuc ngan (15, 30, 60 phut...).

1.8.3. Phan loai theo ban chat Trong moi trng t nhien co nhng chat the hien tnh oc ngay khi

ton tai dang nguyen thuy cua no. Kha nang gay oc cua loai oc chat, oc to nay tac dung vi bat ke nong o (lieu lng) ln hay nho, tc la phu thuoc vao ban chat chnh cua no va sau o mi la nong o hien dien cua no. oc chat ban chat co kha nang c che, gay roi loan sinh ly, gay nguy hai cho sc khoe con ngi va cac sinh vat bat c moi trng nao. V du, mot vai chat oc ban chat nh H2S, CCl4, Pb, Hg, noc ong, noc con bo cap...

Tnh oc cua chat oc ban chat phu thuoc nhieu yeu to nhng quan trong nhat la dang cau truc hoa hoc cua no:

- Chat oc dang hp chat hydrocarbon co tnh oc ty le thuan vi so nguyen t carbon trong phan t.

- Nhng chat vo c co cung so lng cac nguyen to th chat nao co so nguyen t t hn se oc hn.

V du CO oc hn CO2 - So nguyen t halogen thay the hydro cang nhieu th chat o

cang oc: V du CCl4 oc hn nhieu so vi CH3Cl

Sau ay la mot vai v du.

- oc chat thuy ngan (Hg) trong t nhien thng gap di dang cac hp chat vo c nh HgO (mau o), HgCl2, Hg(CN)2... va hu c thuoc y te nh neptan, mercurocrom, thuoc bao ve thc vat, chong nam moc nh serezan, sanesan... Thuy ngan dang ion rat oc. No la chat oc te bao, tac dung cua no rat phc tap. Hg gay thoai hoa to chc, tao thanh cac hp chat protein rat de tan, lam te liet chc nang cua cac nhom

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thiol (-SH), cac he thong men c ban va oxy hoa kh cua te bao. Hg thng tham nhap vao c the theo ba ng: ho hap, da, tieu hoa, chu yeu la qua ng ho hap. Trong mau, khi Hg cua hp chat vo c ket hp chu yeu vi protein huyet thanh th Hg cua hp chat hu c lai gan vao hong cau. Trong than, Hg tch luy phan au cua than, khong tch luy trong cac cuon tieu cau. Trong nao, Hg tch luy nhieu nhat la trong cac te bao than kinh cua chat xam. Ht th Hg vi nong o 0,5 g/m3 khong kh a co anh hng en he than kinh. Hg(CN)2 rat oc, mot ngi khoe uong 0,13 g co the chet sau 9 ngay vi cac trieu chng cua Hg. Thuy ngan co trong cong nghe khai thac quang, ot than (co cha Hg la chat tap)... ac biet hien nay rac thai benh vien thai ra mot lng ln Hg vao moi trng (se trnh bay ky trong chng 5).

Mot so chat oc ban chat trong moi trng khong kh

+ CO: chiem ty le ln trong cac chat gay o nhiem khong kh. Tuy nhien nong o CO trong khong kh khong on nh, bien thien nhanh, ta cha xac nh c chnh xac. CO tch luy trong la lach, khong tch luy trong mau va mat i rat nhanh. Co the gay chet ot ngot ngi va ong vat khi ht th phai luong khong kh CO, v CO tac dung manh vi hemoglobin (Hb), manh gap 250 lan so vi tac dung vi oxy, lay oxy cua Hb va tao thanh carboxyhemoglobin, lam mat kha nang van chuyen oxy cua mau va gay ra ngat th.

Hb.O + CO Hb.CO + O2 Ngoai ra, CO con tac dung vi Fe trong xytocrom-oxydaza (men ho

hap co chc nang hoat hoa oxy), lam bat hoat men, lam cho thieu oxy cang tram trong. oi vi thc vat, CO tac ong t nhay cam hn, nhng khi nong o cao (100 - 10000 ppm trong khong kh) se lam rung la, xoan la, cay non chet, cay coi cham phat trien. CO pha v kha nang ngng ket nit, lam thc vat thieu am.

+ NO tac dung manh vi hemoglobin (gap 1500 lan so vi CO), nhng NO trong kh quyen khong co kha nang tham nhap vao mach mau e tac dung vi Hb.

+ NH3 la kh oc co kha nang kch thch manh len ng ho hap va niem mac am t, gay bong rat do phan ng kiem hoa kem theo toa nhiet. Ngng chu ng la 20 40 mg/m3 khong kh. NH3 thng gay nhiem oc cap tnh.

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Thuoc bao ve thc vat (BVTV) nh dioxin, paraquat, carbamat, DDT... rat oc, tan cong vao he ho hap cua con ngi. D lng thuoc BVTV tren nong san cung tac ong xau cho ngi tieu dung, tan cong vao cac mo, gay d dang, ot bien gen, tac hai lau dai.

Nhng thuoc BVTV tan c trong m nguy hiem hn cac chat oc tan c trong nc. Chung de dang vt qua cac rao can te bao nh pha huy mang te bao, ay Ca ra ngoai, lam ton thng te bao, sau o tan cong vao nhan te bao, lam thay oi enzym, thay oi protein, tao ra mot so phan ng gay bien oi gen, la nguyen nhan gay ung th va tre sinh ra b d dang.

oc to ong vat: nh noc ran, noc ong, ret, bo cap... Tuy nhien vi mot lng cc nho, cac chat nay lai co the dung nh thuoc cha benh.

oc to thc vat: nh cay la ngon, cay cu au, cay thuoc ca.

oc to vi sinh vat: nh vi khuan thng han, tieu chay, viem ai trang... oi vi ngi va ong vat, con oi vi thc vat nh toxine fusarium lycopersici sacc, pseudomonas tabaci...

1.8.4. oc chat trung gian gia hai loai ban chat va lieu lng Co nhng chat co the xep vao loai oc chat nong o - lieu lng

bi ch vi mot nong o vt gii han, no mi the hien tnh oc. Tuy nhien, cung co the xep no vao loai chat oc ban chat v xet mot ieu kien nhat nh, no co the gay roi loan sinh ly, ton thng cho c the neu tham nhap vao cac c quan noi tang.

V du, benzene (C6H6) co the va la chat oc ban chat no la chat oc lieu lng, no co the gay ton thng tuy xng va gay mot chuoi phan ng vi te bao. Khi nong o benzene trong c the cao, tac ong gay hai se keo dai, qua trnh tong hp protein b dng va gay chet te bao. Khi b nhiem oc benzene, benzene c oxy hoa gan thanh phenol ket hp vi acid sulfuric hoac acid glucoronic tao thanh cac acid phenylglucoronic va thai ra nc tieu di dang muoi kiem. Benzene c hap thu qua phoi va da, tan trong m va tch tu trong mo m. Tiep xuc vi nong o benzene cao gay nhiem oc cap tnh, gay choang vang, ngat th, co the gay t vong. Benzene gay ngo oc man tnh tuy xng, gay met moi, xao tron ng da day, thieu mau, lam xao tron DNA di truyen, nhiem sac the bach cau.

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1.8.5. Phan loai theo mc o nguy hiem Mc o nguy hiem cua mot loai oc chat tren mot oi tng

nghien cu xac nh thng c phan loai da theo gia tr LD50 hay LC50. Mc o nguy hiem tuy thuoc vao nhieu yeu to, theo phan loai cua WHO, cac hoa chat co mc o nguy hiem tuy theo dang ton tai va con ng xam nhap vao c the sinh vat th nghiem nh sau:

Bang 1.2. Phan loai chat oc theo mc o nguy hiem. LD50, chuot (mg/kg can nang)

Qua mieng Qua da

Cap oc

The ran The long The ran The long

oc manh

oc

oc trung bnh

oc t

< 5

5 - 50

50 - 500

> 500

< 20

20 - 200

200 - 2000

< 2000

4000

(Nguon: WHO, 1998)

Hau het cac loai thuoc BVTV eu rat oc vi ngi va ong vat mau nong. Tuy nhien, mc o nguy hiem moi loai thuoc khac nhau. Ngi ta chia 2 loai:

Chat oc gay nhiem oc nong o (concentrative poison): mc o gay oc cua nhom chat nay phu thuoc vao lng thuoc tham nhap vao c the. di lieu gay t vong, thuoc dan dan c phan giai va bai tiet ra ngoai c the. Tuy nhien, chung co the gay nhiem oc man tnh cho nhng ngi co thi gian tiep xuc lau. Hp chat thuoc nhom nay gom co lan hu c pyrethroid, cacbamat, hp chat co nguon goc thc vat.

Chat gay nhiem oc tch luy (accumulative poison): la chat co kha nang tch luy lau dai trong c the va gay nhng bien oi sinh ly co hai cho c the song. Ngoai ra, mot so chat co kha nang gay ung th, quai thai va anh hng di truyen oi vi nhng ngi tiep xuc lau dai. Hp chat thuoc nhom nay gom co chlor hu c, hp chat cha As, Pb...

1.8.6. Phan loai theo nguon goc oc chat oc chat trong t nhien xuat phat t nhieu nguon goc khac nhau

nh nguon goc sinh hoa, hoa hoc, chat phong xa... va chnh nguon goc

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nay se anh hng nhieu en oc tnh, mc o gay hai cua chung. Co the phan theo cac nhom: oc to sinh hoc, chat oc hoa hoc, chat oc phong xa v.v

a) oc to sinh hoc

oc to sinh hoc la cac tac nhan c sinh ra t vi khuan, vi trung, oc to tiet ra t thc vat, ong vat, cac san pham cua qua trnh phan huy ong, thc vat chet di tac dung cua vi sinh vat, qua trnh bien oi gen, oc to t cac loai nam, con trung... Noi chung, cac tac nhan oc sinh hoc lam thay oi theo chieu hng xau s phat trien bnh thng cua he sinh thai, i song sinh vat va con ngi.

Cac vi khuan va nam gay benh xam nhap vao c the bang nhieu con ng khac nhau, tuy theo ieu kien moi trng cu the. V du, trong moi trng khong kh neu co vi trung Kock (vi trung lao), de xam nhap qua ng ho hap cho nhng ngi trong vung. Trong nc nhiem ban cung co nhieu loai vi trung, vi khuan, nam lan truyen theo ng nc nh vi khuan ng ruot salmonela typhi va S.paratyphi gay benh thng han, t gap hn la vi khuan l shigella, vi khuan dch ta vibriscomma. Cac vi khuan gay benh oi khi cung ton tai trong cac ong vat nhuyen the; roi thong qua o, gay benh cho cac loai khac nh la mot vat trung gian. Cac loai nam co the gay benh qua ng nc nh loai nam gay benh ngoai da tryco phyton. Cac oc to tiet ra t cac loai nam oc co the gay chet ngi, gay hoai t hoac ung th. Ngoai ra, cac vi khuan, vi rut khong mang oc to cung co the lam thay oi hoat ong cua te bao, gay ot bien.

Nhieu loai ong vat, thc vat mang oc to rat nguy hiem. Nhat la khi b tan cong, chung tiet ra oc chat lam te liet ke thu hoac con moi. V du nh cay la ngon, noc ran, dch tiet ra t con sa, bo cap...

b) Chat oc hoa hoc

Trong t nhien, cac oc chat co nguon goc t hoa chat, la san pham cua cac phan ng hoa hoc, t cac nganh cong nghiep, chat thai cong nghiep... c xep vao loai oc chat hoa hoc. Rat nhieu oc chat co nguon goc t hoa chat. Mc o gay oc cua chung tuy thuoc nhieu vao cau truc hoa hoc, nong o tac ong cua chung va trang thai cua c the nhan chat oc.

Chat oc co nguon goc hoa hoc co the ton tai ba dang: ran, long, kh.

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Tuy theo kha nang phan tan vao c the con ngi ma tac dung gay oc cua moi dang khac nhau. Cac chat kh de tham vao c the ngi nen mc o gay oc cung cao hn chat long va ran. Ngoai ra, oc tnh cua moi loai con tuy thuoc vao tnh chat vat ly, cau tao hoa hoc ma co cac mc o oc khac nhau.

c) Chat oc phong xa

Tia phong xa la nhng tia mat thng khong nhn thay c, phat ra t cac nguyen to phong xa nh uranium, cobalt, radium... Hat nhan nguyen t phong xa co the phat ra cac tia nh sau:

- Tia la chum hat nhan mang ien tch dng. Khoi lng hat bang 4 va ien tch hat bang 2, chnh la chum hat nhan nguyen t heli. Kha nang xuyen qua vat chat kem nhng kha nang gay ion hoa rat ln. Trong khong kh, tia i c 10 - 20cm, c moi mm ng i tao c 6000 ion.

- Tia la chum hat ien t ien tch bang 1 va khoi lng khong ang ke, co kha nang am xuyen manh hn tia . Trong khong kh tia i c mot oan ng dai gap 10 lan tia , c 1mm ng i, tao c 6 ion. Tia + la nhng hat co khoi lng bang khoi lng hat ien t va mang ien tch dng, c tao ra do s phan huy cua mot so ong v phong xa nhan tao.

- Tia la mot bc xa ien t phat ra t hat nhan nguyen t, co toc o bang van toc anh sang. No gay ra hien tng ion hoa gian tiep nh ba hieu ng quang ien, Compton va sinh oi hat nhan. Tia co kha nang xuyen qua vat chat manh, muon can no phai dung tam ch hoac be tong day.

Anh hng cua tia phong xa: tia phong xa khi chieu t ngoai vao be mat c the tao ra mot tac dung goi la tac dung ngoai chieu.

Chat phong xa xam nhap vao c the (qua ng ho hap, tieu hoa) ti cac c quan, sau o gay tac dung chieu xa th goi la tac dung noi chieu. Tac dung nay nguy hiem hn tac dung ngoai chieu.

Nan nhan nhiem phong xa co the hai dang: nhiem oc cap tnh va man tnh.

Cap tnh Phat benh rat nhanh sau khi nhiem phong xa vai ngay hoac vai gi. Khi

c the b nhiem xa toan than mot lieu tren 300 Rem, co cac trieu chng:

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- Roi loan cac chc nang than kinh trung ng, ac biet la vo nao, cam giac met moi

- Da b bong cho tia phong xa i qua - C quan tao mau b ton thng nang ne - Lien ket hoa hoc cua DNA trong te bao b be gay - Suy nhc c the dan en chet.

Nhiem xa cap tnh ch xay ra trong cac vu no hat nhan, s co trung tam nguyen t, t gap trong cac ieu kien san xuat va nghien cu.

Man tnh Cac trieu chng xuat hien muon vai nam en vai chuc nam sau khi

b nhiem xa. Turk (1984) cho biet, khi con ngi hay sinh vat tiep xuc vi nguon phong xa t mot 100 - 250 Rad th khong chet, nhng met moi, non ma, rung toc, xuat hien cac mam mong cua benh ung th.

1.8.7. Phan loai theo trang thai ton tai a) Trang thai hoa hoc Cac chat oc ton tai dang khac nhau: n chat hay hp chat, dang

ion hay phan t th kha nang gay oc cung khac nhau. V du, trong day ion cua nhom Al3+, Al(OH)2+, (AlOH)2+, Al(OH)3, Al(OH)4- th dang Al3+ va (AlOH)2+ la cac dang oc chat. Moi trng ton tai hoa chat cung gop phan lam tang hay giam thieu oc tnh. V du :

- S hien dien cua calcium nong o ln co the lam giam tnh oc cua nhieu kim loai.

- Chat hu c trong at va at set co the ket hp vi nhau va gop phan co nh cac kim loai, lam giam oc tnh.

- Moi trng co tnh acid thng lam tang tnh hoa tan cua oc chat, tang hoat tnh.

- S hien dien cung mot luc cua nhieu oc to, oc chat se lam cong hng tnh oc hay lam triet tieu tnh oc cua nhau.

- Nong o oxygen, ien the oxy hoa - kh co the anh hng manh ti tnh hoa tan cua oc chat.

- Tnh tham thau cua dung dch at la ham so cua nong o tong cong cua ion oc tiem tang, do o anh hng manh en kha nang tham nhap hay sinh ra oc chat.

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b) Trang thai vat ly

Trang thai vat ly cua oc chat co the the ran, long, kh, hi, bui... Mc o gay oc cua chat oc tang dan t the ran, sang long va cao nhat la the kh. Kha nang gay oc thay oi theo trang thai vat ly cua oc chat phu thuoc vao mc o khuech tan cac oc chat vao moi trng.

1.8.8. Phan loai thong qua ng tham nhap va gay hai Chat oc tham nhap vao cac oi tng trong he sinh thai bang

nhieu con ng, cach thc khac nhau. Cac cach thc nay cung quyet nh en mc o tac hai ma oc chat anh hng len ong vat, thc vat va con ngi. Du bang con ng tham nhap nao th khi vao trong c the sinh vat va con ngi, oc chat cung gay ra s mat on nh cua cau truc vat chat trong c the, nhng neu biet trc con ng cua moi loai, chung ta co the phong nga tch cc. V vay, phan loai oc chat theo cach thc tham nhap cua chung la mot cach phan loai hp ly. V du, cac chat nhiem oc the kh tham nhap vao c the qua ng ho hap de hn cac chat the long va ran, do o, co the phan loai cac chat oc dang kh thuoc nhom gay nhiem oc qua ng ho hap. Tuy nhien, trong nhieu trng hp, cach phan loai nay khong hoan toan ung. V du, thuy ngan bnh thng trang thai long nhng co the gay nhiem oc cap thong qua ng ho hap do s de bay hi cua no.

Tm hieu tren moi loai oi tng b au oc se cho chung ta nhng nhom oc chat va cach thc i vao c the cua chung.

oi vi thc vat

- Tham nhap chu ong: tham nhap mot cach t nhien thong qua tiep xuc, trao oi chat. Chat oc ( dang ran, long, kh) co trong moi trng o nhiem se tham nhap qua tiep xuc trc tiep va trao oi chat vi thc vat, thong qua kh quyen, at, nc co cha cac thanh phan oc hai. V du, cac kim loai nang, acid, base... trong at, tham nhap vao c the thc vat thong qua bo re, sau o tch tu trong than cay, lau dan pha v cau truc te bao cay, gian tiep gay oc cho ong vat an phai chung.

- Tham nhap thu ong: tham nhap bang tng tac nhan tao, v du nh qua phan bon, thuoc kch thch tang trng c bon cho cay.

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oi vi ong vat

oc chat tham nhap vao c the ong vat va con ngi qua ba ng: tiep xuc qua da, qua ng ho hap, ng tieu hoa. Do o, oc chat cung c phan loai da vao con ng ma oc chat co the tien vao c the ong vat va gay hai.

1.9. OI TNG NGHIEN CU CUA OC HOC MOI TRNG oc hoc moi trng nghien cu cac oi tng:

+ Cac anh hng cua oc chat (hoa, vo c, hu c t cac qua trnh o nhiem moi trng), cac oc to sinh hoc (oc to ong thc vat, vi sinh vat) va ke ca oc to t ngi benh tiet ra, len:

- Cac ca the sinh vat

- Quan the

- Quan xa

- He sinh thai - quan c xa hoi con ngi.

+ Cac anh hng cua oc chat oc to len "vi a sinh thai" va "trung a sinh thai" (terreotrial microcosms and mesocosms)

- Nhng thay oi (thng la yeu i) cua he thong sinh hoc va chc nang sinh thai cua he sinh thai moi trng.

- S ton hai cua sinh vat va con ngi (b benh, yeu hoac chet i).

- Thay oi ve so lng loai, tuoi, cau truc, kch thc hoac nhng loai mi xuat hien trong qua trnh tac ong cua oc chat hay oc to.

- Thay oi ve phan bo di truyen

- Thay oi ve s phat hien thc vat, nang suat sinh khoi.

- Thay oi toc o va mc o ho hap trong at (ngi ta phai dung cac ky thuat o lng O2 vao lng CO2 thai ra t at). Qua trnh nay chu yeu la do vi sinh vat at tao nen. Shirazi (1992), a chng minh cac d lieu ve o oc hai cua cac kieu loai trong cac loai at khac nhau lien quan en ac tnh at - bieu hien qua trao oi O2 va CO2. Qua trnh ho hap, theo Gile (1979), lam cho nong o cua hexachlorobenzene, petachlorophenol va parathion thay oi, ma thong qua hoat tnh cua cac hoa chat nay se lam hao hut cac nguyen to vi lng.

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- oc chat va oc to lam thay oi cac ham lng cua cac vi lng va a lng trong moi trng thanh phan.

- Thay oi ac tnh va tap tuc sinh hoc cua vi sinh vat va tng tac gia cac chung loai trong he sinh thai vi nhau.

- Thong qua day chuyen thc pham, tch luy va phong ai sinh hoc (bioaccumulation, bioesaggeration) oc chat ton tai va gay hai toan bo he thong sinh thai moi trng.

Cau hoi 1. Hay neu nhng hieu biet c ban cua ban ve oc hoc moi trng? 2. Hay trnh bay mot so khai niem : oc to hoc moi trng, tac nhan

gay o, lieu lng oc, o oc cap tnh va o oc man tnh. 3. Hay ke nhng nguyen ly c ban ve oc hoc moi trng? 4. Cac yeu to anh hng en o oc cua chat oc va oc to? 5. Hay ke cac con ng xam nhap cua chat oc vao c the? 6. Cac yeu to lam tang, giam oc tnh cua oc chat, oc to 7. Hay neu ten mot vai loai oc chat ien hnh va cac anh hng

cua no en sinh vat va con ngi. 8. oi tng nghien cu cua mon oc hoc moi trng la g? 9. Theo nguon goc th oc chat, oc to co the chia ra thanh nhng

loai nao? 10. Neu cac nguon phat sinh ra oc chat oc to?

Tai lieu tham khao 1. Tran T An, Bai giang kiem nghiem oc chat hoc, NXB Y hoc,

Ha Noi, 1984 2. Bo khoa hoc cong nghe va moi trng, Mot so tieu chuan tam

thi ve moi trng, NXB Khoa hoc va k thuat, Ha Noi, 1993 3. Le Van Khoa, Moi trng va o nhiem, NXB Giao duc, Ha Noi,

1994 4. Tran Kien, Sinh thai hoc c ban, NXB Khoa hoc va k thuat, Ha

Noi, 1997 5. Nguyen Van Tuyen, Sinh thai va moi trng, NXB Giao duc, Ha

Noi, 1997

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6. Mai nh Yem, C s sinh thai, NXB Khoa hoc va k thuat, Ha Noi, 1995: 66-70

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CHNG 2

OC HOC MOI TRNG AT, TRAM TCH () (SEDIMENTAL - SOIL ECOTOXICOLOGY)

2.1. TONG QUAN

2.1.1. oc chat trong moi trng at

Cac oc chat nay co the ton tai di nhieu dang khac nhau nh: vo c, hu c, hp chat, n chat, ion, chat long, chat ran, chat kh. Trong moi trng sinh thai at, cac oc chat pho bien va gay tac hai nhieu nhat thng ton tai di dang ion. Co hai dang oc chat trong moi trng at ang quan tam la oc chat theo ban chat va oc chat theo nong o. Du la dang nao th cac oc chat nay eu co tac dung xau en s sinh trng va phat duc cua cay trong va sinh vat song trong at hay sinh vat tiep xuc vi at. Ta se xet hai loai oc chat trong at:

oc chat theo ban chat: la nhng chat oc co kha nang gay oc moi nong o du thap hay cao. V du: cac chat H2S, Na2CO3, CuSO4, Pb, Hg, Cd, Be, St

oc chat theo nong o: oc chat dang nay eu co nong o gii han cho phep oi vi moi loai cay noi rieng va sinh vat noi chung. Neu vt qua gii han nay th cac chat mi co kha nang gay oc. Cac oc chat dang nay thng la: H+, Al3+, Fe2+, SO42- , OH+, Mn2+, Na+, NH3, NH4+, NO2. Cac kim loai nang nh: Pb, As, Cu, Hg, Ca

V du: khi nong o cac cation Ba2+, Mg2+, NH4+ vt qua 1/5000, 1/4000, 1/500 (ve trong lng) thng gay oc cho cay trong, con Fe2+ vt qua 500 ppm, Al3+ vt qua 135 ppm gay oc cho lua.

2.1.2. Con ng xam nhap cua oc chat t at vao c the sinh vat

Co hai giai oan hap thu oc chat t moi trng at vao c the sinh vat.

Giai oan 1: c the sinh vat han che s hap thu.

Xem them Sinh thai moi trng at, Le Huy Ba, Nxb Nong nghiep, 1996.

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Giai oan 2: hap thu b ong, chat oc xam nhap pha v mang te bao, i vao cac c quan va lan toa trong c the sinh vat.

oi vi thc vat - Trng hp 1: oc chat thng c hap thu qua re. Qua trnh nay

c chia thanh hai giai oan: giai oan au chu ong hap thu trao oi. en khi cay co bieu hien nhiem oc, thc vat se han che s hap thu, ong thi o cung la phan ng t ve cua thc vat khi nhan ra chat oc. Chnh v vay ma nhieu loai thc vat song trong moi trng at, oc chat tch luy nhieu re, t than la va rat t hoa, qua, hat. o la s phan ve cua thc vat.

- Trng hp 2: la s xam nhap n thuan do khuech tan t nong o oc cao trong dung dch at vao c the thc vat. Hien tng nay xay ra manh khi s e khang cua cay khong con na, kha nang hap thu co chon loc cua cay a mat hoac yeu han i.

oi vi ong vat oc chat i t moi trng at qua hai con ng xam nhap cua chat

oc vao c the: con ng gian tiep qua thc an, thc pham trung gian va con ng xam nhap chat oc trc tiep qua da roi vao c the.

2.1.3. C che xam nhap cua oc chat vao at Keo at la hat vat chat mang ien c cau tao bi bon lp ke t

trong ra ngoai la: 1. nhan, 2. lp ion quyet nh the thng la mang ien tch am, 3. lp ion khong di chuyen mang ien trai dau vi lp ion quyet nh the, va 4. lp ion co kha nang trao oi ien tch vi moi trng ben ngoai. Vi cau truc nay, keo at co kha nang hap thu trao oi ion gia be mat cua keo at vi dung dch at (soil solution) bao quanh no. S xam nhap cua oc chat vao moi trng at c thc hien thong qua hoat tnh cua keo at va dung dch at.

2.1.4. Cac yeu to anh hng en oc chat trong moi trng at a) Ban chat cua cac chat oc oi vi loai sinh vat hay con goi la tnh

k sinh vat: Tnh oc cua cac chat nay c quyet nh bi cau tao va hoat tnh cua chung. V du: Pb, Hg, CuSO4 th luon luon oc oi vi sinh vat. Nhng chat khong k sinh vat th tnh oc bieu hien thap hn.

b) Nong o va lieu lng cua oc chat co tng quan thuan vi tnh oc. Nong o va lieu lng cang cao th cang oc.

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c) Nhiet o: nhiet o at cang cao th tnh oc cang manh (tr phi chung iem phan huy cua chat oc). Nhng cung co the khi nhiet o at qua cao se lam phan huy oc chat.

d) Ngng chu oc: cac loai sinh vat khac nhau co ngng chu oc khac nhau. Tuoi tac: sinh vat non tre th man cam vi chat oc, ngng chu oc thap; sinh vat cao tuoi th ngng chu oc cao, nhng tuoi gia chu oc kem. Gii tnh cung anh hng en ngng chu oc. Giong cai va phai n th de man cam vi chat oc hn la giong c va phai nam.

e) Nhng ieu kien khac cua at: che o nc, o am, o chua trong at co anh hng en s cung cap O2 e giai oc va phan bo lai nong o cua hi oc.

g) Kha nang t lam sach cua moi trng at: c goi its self puryfication hay Soil Detoxification. Kha nang nay rat ln, nhng moi loai at co kha nang khac nhau. Nh vay ma cac sinh vat trong at t b nhiem oc hn trong moi trng nc va moi trng khong kh.

2.2. CAC DANG NHIEM OC TRONG MOI TRNG AT Moi trng at co the b nhiem oc do s lan truyen t moi trng

khong kh, nc b o nhiem hay xac ba ong thc vat ton tai lau dai tren mat at, trong at, lam cho nong o cac oc chat tang len, vt qua mc an toan va gay ra o nhiem va sau o la nhiem oc he sinh thai at.

a) Nhiem oc do o nhiem t nhien

+ Nhiem phen: do nc phen t cac ron phen (trung tam phen) theo dong nc mat hoac nc ngam lan en v tr khac lam nhiem phen ni nay. Dang nhiem phen nay chu yeu la nhiem cac chat oc Fe2+, Al3+, SO42- ong thi lam cho nong o cua chung trong dung dch at, keo at tang len cao. ong thi, nhiem oc phen cung lam pH cua moi trng at giam xuong. Ket qua, gay ngo oc cho cay trong, sinh vat trong at.

+ Nhiem man: nhiem man gay ra do muoi trong nc bien, nc trieu hay t cac mo muoi, trong o co cac chat oc Na+, K+, Cl-, SO42-, CO32- . Chung gay hai do tac ong ion, cung co the gay hai bi ap suat tham thau. Nong o muoi cao trong dung dch at gay han sinh ly cho thc vat.

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+ Gley hoa: qua trnh gley hoa trong moi trng at la qua trnh phan giai chat hu c trong ieu kien ngap nc, yem kh, ni tch luy nhieu xac ba sinh vat, san sinh ra nhieu chat oc di dang CH4 , H2S, N2O, CO2 , FeS va cac acid hu c khac o la nhng chat gay oc cho sinh thai moi trng.

b) Nhiem oc do o nhiem nhan tao

- O nhiem dau: lam giam hieu qua cua trang thai at oi vi ong vat va thc vat.

- O nhiem kim loai nang (t nc thai hay bui cha nhieu kim loai nang) gay nhiem Hg, Pb, Cu, Cd.

- O nhiem chat hu c: gay ra bi s tch tu xac ba hu c do rac thai hu c khu dan c, cac bai rac o th, vt qua kha nang t lam sach cua moi trng at, tao ra cac kh oc: CH4 , H2S, cac acid hu c va d tha vi sinh vat yem kh, vi khuan gay benh.

- O nhiem do chat phong xa: do cac phan ng neutron hoa tac dung neutron len cac protein, t cac vu no bom H va do tac dung bc xa vu tru, lam sinh ra cac chat phong xa. Khi cac chat nay xam nhap vao moi trng at, no se xam nhap vao cac thc vat, ong vat trong cac chu trnh sinh a hoa hay qua day chuyen thc pham.

- O nhiem vi sinh vat trong moi trng at: vi trung gay benh co mat trong at nhieu hn ve chung loai va so lng co the so vi trong nc. Kha nang sinh soi nay n va lan truyen benh cua chung cung cao nh trong moi trng nc va khong kh.

- O nhiem hoa chat nong nghiep: cac chat hu c, hu vo c, hay c kim thng co ac tnh ben vng trong moi trng at, nen no co cac tac ong gay oc trc tiep hoac tiem tang va nguy hiem oi vi con ngi. oc chat trong at co the truyen trc tiep vao sinh vat va ngi khi tiep xuc va cung co the qua con ng thc pham: at cay ong vat an thc vat con ngi

c) oc chat trong at va mo hnh QSAR

S lan truyen o nhiem va viec e ra ke hoach cai tao, bao ton at nong nghiep gap kho khan trong qua trnh tap trung chat o nhiem nang. Co the s dung vi sinh vat e phan giai mot so oc chat sinh ra t cac chat o

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nhiem co quy mo ln gay anh hng en cac hoat ong trong trot (nh CxHy sinh ra trong dau mo va san pham dau, hoac chat hu c hoa tan). Nhng oc chat khong co thuoc ac tr la nguyen nhan e chat o nhiem hoa tan vao nc gay ra tnh trang lan rong o nhiem thanh cac mang o nhiem (Baughman va Paris, 1981). Hang loat mang te bao b phan huy tao ra cac mang o nhiem hu c cha cac dang hu c vi sinh vat (Bitton va ong nghiep, 1988; Sikkema cung ong nghiep, 1995). Ket qua cac mang nay lam cho nhng chat o nhiem tang tnh tham qua mang. Qua trnh quang hp 14oC cua cac te bao cua tao lam mat i kali trong tao (Hutchinsonquy va ong nghiep, 1981) va vi khuan (Bernheim, 1974).

S phat trien cua chat oc do o nhiem hu c lam pha v can bang sinh hoc va gay oc ly hoa. Nhng mau nay c quy thanh nh lng cau truc hoat ong van chuyen (QSAR). Mo hnh toan QSAR cho phep mieu ta cach dung phng phap d oan oc chat cua cac hu c phi kim loai co anh hng en s a dang sinh hoc cua vi sinh vat va hng dan cach s dung vi sinh vat co ch vao thc te (Blum va Spcue, 1990). S mo ta ve be mat a hnh cua mot oc chat bang mo hnh QSAR c Warne cung ong nghiep tm ra vao nam 1988. Trong mo hnh nay, ong a tm ra sc manh ket hp gia s phat trien va tap quan ton tai cua vi khuan trong cac thanh phan cua mang dau bao gom alkyl-subotituted benzene, napthadium pyridin va phenol. Tng t, nhng nghien cu bo sung tiep theo a tm ra oc chat cua mono, di, tri, tetra va pentachlorophenol ong vai tro quan trong trong s phat trien cua cac vi khuan at (Liu va ong nghiep, 1982). Vi phng phap nay, ngi ta lam tang tnh chlor hoa cua phenol.

d) Vi sinh vat va oc chat, oc to trong at

Cac chat hu c co nguon goc t nhien co anh hng en s ton tai, hoat ong va phat trien cua vi sinh vat trong moi trng at.

Cac chat benzene, oxy thm (benzenoate hay phenol) va alkyltaled thm (toluene) co xu hng lam giam a dang sinh hoc cua vi sinh vat at di cac ieu kien k kh. NO3-, Fe hoac SO42- co gia tr s dung nh chat cho - nhan ien t (Lonergan, 1990). ieu kien cho, the nang cua vi sinh vat k kh b suy thoai do hydrocarbon hexandecan co nong o di mc bnh thng (Aeekersberg va ong nghiep, 1991). S phan giai sinh hoc cua nhieu hp chat c tao bi cac hoat ong cua vi khuan k

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kh va thi iem ton tai cua vi sinh vat k kh trong moi trng. S phan giai cua vi sinh vat k kh co the em lai li ch cho moi trng va lam giam mot lng ln chat o nhiem (Loviety va ong nghiep, 1995). Mat khac, s suy giam cua vi sinh vat k kh cung cap them thong tin cho van e nay.

Tan tch sinh vat cua cac chat trong hien tng o nhiem hu c, ma trong chung cha nhieu thanh phan cacbon va hydro la nhu cau can thiet cung cap mot lng chat ban au cho qua trnh thay oi oc tnh. S thay oi, suy giam cua hydro phu thuoc vao nhiet o va theo mua.

S giam H2 xay ra mot khoang nhiet o gia mua ong lanh en -30oC (Foght va Weslake, 1987). Vi trung co the chu nhiet o cc cao (Leahy va Colwell, 1990). Tuy nhien, s suy giam H2 se xay ra trong moi trng t nhien (Palmisano va ong nghiep, 1991).

Trong at, ty le suy giam cua H2 thng khong cao khi ieu kien kiem, cao hn la ieu kien acid. Moi trng acid tao ieu kien phat trien cho nam, chung la thanh phan cua H2 nhng thng co ty le thap hn vi khuan. Chung thch nghi vi ham lng nit ngng kiem (Hambruk, 1980). Trong moi trng at, pH co tac ong en s suy giam cua H2 tram tch cha muoi. pH cua tram tch tang t 6,5 - 8,0 nhng cac mau tram tch khac nhau co pH cung khac nhau, ty le suy giam cua H2 pH = 5,0 va pH = 6,5 thap hn pH = 8,0.

ieu kien tot nhat e co o dan ien thch hp vi vi sinh vat hieu kh trong at la kha nang gi nc (WHC) t 50 - 70%, chung phat trien tot nhat khi o dan nc khoang 0,98 - 0,99 (Attlas va Bartha, 1993). Nc cat co gia tr EC = 1. Trong moi trng at, o dan ien cua nc trong at co the b gii han bi nguon goc cua no. Ty le cua mang dau co anh hng en s chuyen hoa sinh hoc trong at khi WHC co gia tr t 30 - 90%. S phan huy H-C tot nhat vi mot lng nho hn trong nc hoa tan. Nc co vai tro quan trong trong viec phan huy H-C trong at.

Cac phan ng bien oi cua cac chat hu c trong moi trng at thng dien ra nhanh. Tuy nhien, nhng hp chat kho phan huy nh thuoc tr sau th co cac phan ng phan huy dien ra cham hn.

Tren be mat cua oxy, nhng vi sinh vat hieu kh se oxy hoa hoan toan cac carbon trong t nhien thanh CO2. Oxy c s dung giong nh

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chat cho - nhan ien t (oxy co nguon goc t nc). Tuy nhien, oxy thng ong vai tro chu chot trong qua trnh sinh trng va phat trien cua cac te bao.

e) S bien oi sinh hoc cua oc chat trong at: thng nhng san pham trung gian cua qua trnh bien oi sinh hoc co the oc hn hp chat ban au.

Thuoc BVTV: thuoc diet co duiron va propamat a giam trong at nhng khi gii han cho phep la > 5mg/kg co the ngan can hoat ong cua vi khuan mitrifying trong at (Thompson va Corke, 1969). Short cung ong nghiep (1991), thc hien phan tch, nghien cu trong at vi chat chung la acid 2,4 diclorophenolxyaxetic (2,4 D) a rut ra ket luan qua trnh nay lam giam pseudomnas putida PP0301. Trong o, vi khuan lam giam nong o cua 2,4 D t 500 mg/l en 100 mg/l. S dao ong nong o 2,4 D t 10 en 25 mg/l co the lam ngan can s phat trien cua cac loai nam noi chung.

Nh vay, phuc hoi bang bien phap sinh hoc cho cac trng hp at o nhiem la can thiet va mang lai tnh hieu qua cho viec giam bt hay chuyen hoa cac chat o nhiem hu c, tc la lam giam oc to cho moi trng at.

2.3. CAC CHAT OC TRONG AT NGAP NC, YEM KH - TAC HAI CUA CHUNG, BIEN PHAP PHONG CHONG

2.3.1. Cac oc chat trong at ngap nc

2.3.1.1. Mot so chat ien hnh

at ngap nc la mot moi trng yem kh, viec phan huy yem kh cac chat t rac thai hu c, tan tch sinh vat, thong qua hoat ong vi sinh vat se lam sinh san mot so chat ma khi nong o vt qua mc o cho phep se tr nen oc oi vi cac thuy sinh vat. Cac oc chat chnh cua qua trnh phan huy yem kh chu yeu la cac chat: H2S, NH4+, P, S, kim loai nang. Cac oc chat nay t nhieu cung co cac tac ong tieu cc en i song cua sinh vat trong moi trng at ngap nc. Tuy nhien, vi kha nang thch ng cua mnh, cac sinh vat a co c che hoat ong thch hp e ton tai va phat trien c trong moi trng nay. Trong ieu kien at ngap nc hoan toan, th tnh trang yem kh luon tao nen cac qua trnh kh trong at

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va hnh thanh cac san pham: Fe2+, Mn2+ (kh Fe3+ thanh Fe2+, Mn4+ thanh Mn2+), SO32-, (kh sulfate thanh sulfide) va NH4+ t NO3-. ong thi sinh ra nhieu oc chat trong at nh CH4, H2S, FeS2 cung vi hang loat vi sinh vat, gay tac ong xau en moi trng.

Theo Van Ranst (1991), phan ng kh manh co the xay ra trong nhng tram tch cha mot lng ln cac chat hu c va b tram lang thng xuyen ma ta thng thay cac vung ngap nc ven bien. Neu san pham cua Fe3+ co mat trong vat lieu c chuyen en do song va muoi SO42- co mat trong moi trng nh trong chat hu c hoac hoa tan trong nc ngam, chung se c s dung nh nhng chat oxy hoa bi he ong vat at song trong cac tan d thc vat.

Cac phan ng tao ra kh H2S dien ra trong at ngap nc: Na2SO4 + CH4 2Na+ + S2- + CO2 + 2H2O S2- + H2O HS + OH- HS + OH- H2S + OH- Phan ln cac phan ng trong ieu kien yem kh la nhng phan ng

sinh hoa, co s tham gia cua cac vi sinh vat trong at. ong thi, cac phan ng nay cung la nhng phan ng oxy hoa - kh vi cac chat nhan va cho ien t. Phan ng tao ra Fe2+ va sulfide trong at c the hien di dang phng trnh ien t rut gon nh sau:

S2- + Fe2+ FeS 2S2- + Fe2+ FeS2 + 2e- SO42- + 8H+ + 8e- S2- + 4H2O Fe3+ + e- Fe2+ Ngoai ra, trong ieu kien yem kh, san pham cua qua trnh co s

tap trung cua mot lng kha ln kh CO2, H2, CH4 va N2. Mot trong nhng qua trnh kha quan trong trong at ngap nc, ma

thong qua no nhieu oc chat c sinh ra trong at la qua trnh gley hoa vi cac bc sau:

1) S mat oxy do b ngap nc va lay i oxy do s ho hap cua vi sinh vat hieu kh.

2) S kh nitrate do vi sinh vat s dung no nh nhng chat nhan ien t thay the cho oxy. Ket qua cua qua trnh nay sinh ra NO, N2O, va N2 trong at.

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3) S chuyen hoa goc methyl cua cac acid acetic va mot phan t goc CO32- trong at.

Nh a e cap ve s kh Fe3+ thanh Fe2+ cung vi s tham gia cua cac vi sinh vat ma ac trng la s ho hap cua vi sinh vat yem kh, cac chat hu c cao phan t bien oi va phan giai thanh cac acid hu c va sau o nh vi khuan bacteria methane e tr thanh CH4.

Trong moi trng yem kh, cac chat co qua trnh bien oi khac nhau, tuy thuoc vao san pham cua qua trnh bien oi ma chung co the c coi la chat oc hoac khong oc. Dien bien oc chat cua mot chat chnh trong moi trng at ngap nc c trnh bay nh sau:

+ Nitrogen: trong at, nitrate thng b thay the bi cac amonium, du s hap thu cua thc vat lai dang nitrate. Tuy nhien, s thay oi nay trong cac can ay cho thay chung co kha nang duy tr ty le nitrogen mc bnh thng. Kha nang nay lien quan en ba qua trnh chnh:

- Kha nang oxy hoa amonium thanh nitrate trong bo re thong qua viec lay oxy t cac long hut.

- Mot so loai ac biet co kha nang hap thu amonium mot cach trc tiep.

- Kha nang hap thu cua cac loai thc vat e duy tr hoat ong trao oi chat hap thu, chat dinh dng.

Nh vay, hoat ong yem kh a lam thay oi qua trnh bien oi am cua moi trng at. Tuy nhien, anh hng oc en hoat ong cua sinh vat la khong cao.

+ Sat va mangan: Nhu cau ve Fe va Mn cua cay trong ch mc rat thap. V vay, chung co the se at en mc o oc hai rat nhieu moi trng khac nhau. Hai nguyen to nay eu b bien oi va tr nen giau hn trong at ngap nc. Ham lng cua sat va mangan tham gia vao cac hoat ong trao oi cation va tch tu lai trong cac mo cua thc vat. Thc vat ngap nc chu ng c hai nguyen to nay ch la nh vao mot so thch nghi rieng: Th nhat la kha nang oxy hoa cua bo re co the co nh va bien oi chung xuong en mot nong o thch hp. Th hai, nhieu chat khoang tham vao ben trong cac mo co the c tch tu lai trong cac khoang bao cua te bao, trong cac khoang bao cua cac mam choi. o, chung khong tac ong en s trao oi chat cua te bao chat. Th ba, nhieu loai thc vat ngap nc xuat hien mot c che co the s dung mot ham

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lng hai nguyen to nay (Fe, Mn) cao hn mc thch ng trao oi chat trung bnh.

+ Lu huynh: lu huynh xuat hien di dang sulfide th rat oc oi vi cac mo thc vat. Lu huynh b bien oi thanh dang sulfide trong qua trnh phan huy yem kh trong at va tch luy en nong o gay oc trong am lay ngap man. S thch ng vi nong o sulfur cao cua thc vat ngap nc co bien o thay oi rong. Cac loai thc vat khac nhau th co kha nang chu oc khac nhau. o la nhng c che thch nghi vi viec oxy hoa sulfide thanh sulfate, tch tu sulfate trong cac khoang bao. ac iem nay chung ta thay moi trng at ngap nc cua rng ngap man ven bien.

2.3.1.2. Tac hai cua cac oc chat

Cac chat c sinh ra trong ieu kien yem kh c xem nh nhng oc chat co kha nang gay hai cho sinh vat. V du: lng Fe2+ va H2S trong at cao se lam bam vao re lua, lam rung long hut, re en, cha nhieu FeS, roi thoi dan co khi ca cay lua b chet. Mat khac, H2S cung gay tac hai lam mot so nhom thc vat b ngo oc, cay phat trien kem va chet.

Qua trnh gley hoa a lam cho moi trng at b chua hoa do qua trnh kh sinh ra mot so acid hu c, hoac mat am do N2 bay hi, H2S lam ngo oc re thc vat, gay chet cho ong vat va mot so vi sinh vat hieu kh trong moi trng at. Cac kh CH4, NO2, NO va CO2 con gop phan gay ra 15% hieu ng nha knh.

2.3.1.3. Bien phap phong chong

e han che hien tng ngo oc cho cac sinh vat tren vung at ngap nc, yem kh, bien phap hu hieu nhat la lam cho at c luan phien thoang kh. S oxy hoa trong at xay ra lam cho nong o cac chat oc c giam xuong di ngng gay oc cho sinh vat (ngoai tr at phen tiem tang).

2.4. CAC CHAT OC TRONG