9
Articles Risk Screening for Exposure to Groundwater Pollution in a Wastewater Irrigation District of the Mexico City Region Timothy J. Downs,12 Enrique Cifuentes-Garcia,3 and Irwin Mel Suffet1 1Environmental Science and Engineering Program, UCLA School of Public Health, Los Angeles, California, USA; 2lnstituto de Salud, Ambiente y Trabajo, Tlalpan, Mexico City, Mexico; 3Departamento de Salud Ambiental, Instituto Nacional de Salud Publica, Cuernavaca, Morelos, Mexico Untreated watewater from the Mexico City basin has been used for decades to irrigate cropland in the Mezquital Valley, State of Hidalgo, Mexico. Excess irriion water rechargs the near-sur- fIae aquifer that is used as a domestic water supply source. We assesse the groundwater quality of three key groundwater sources of domestc water by ng for 24 trace metals, 67 target base/neutrlacid (BNA) organic compounds, nontarget BNA organics, 23 chlorinated pesticides, 20 polychlorinated biphenyls, and nitrate, as well as microbiological contaminants-coliforms, Vibrio cholerae, and Salmonella Study participants answered a questionnaire that estimated ingestion and dennal exsure to groundwater, 10% of the sample reported frequent diarrhea and 9% reported persistent skin itriations. Detection of V cholerae non-1 in surface waters at all sites suggested a potential risk (surrogate indicator present) of diarrheal dise for canal and river bathers by accidentl ingestion, as well as potential VI/Prio contamination of near-surface groundwater and potential cholera sk m ified by lapses in disinfection. High total coliform levels in surfae water and lower levels in groundwater at all sites indicated fcal contamiaion and a potential risk of gasointestinal in populations exposed to inadequately disinfected groundwater. Using chemical criteria, no significant risk from ingstion or dermal contact was identified at the method detection limits at any site, except from nitrate exposure: infants and young children are at risk from methemoglobinemia at all sites. Results suggest that pathogen risk imterventions are a pnonty, whereas nitrate risk needs fiuther characterization to determine if formal treatment is needed. The risks exist inside and outside the irrigation district. The method was highly cost-effective. Kq words; groundwater, Mexico, nitrate, pathogens, risk, wastewater irrigation. Environ Healtb Prspect 107:553-561 (1999). [Online 3 June 1999] hap :I/ehpnetl.niehs.nib.gov/docs/1999/107p553-561downs/abstrabhl Mexico City and the Valley of Mexico indis- putably provides one of the best examples of a development model in crisis. Of the current average Mexico City wastewater flow of 45 m3/sec, approximately 75% is used, without formal treatment, to irrigate 90,000 ha in the Mezquital Valley, State of Hidalgo (1). The total human exposure implications of this water have yet to be explored. The main epi- demiologic research in the region has report- ed significant diarrheal disease and parasitic infections in farm workers and their families (). In the most recent review of the environ- mental impact of using wastewater for irriga- tion (arguably the largest such region in the world), the lack of attention to drinking water in the zone and potential groundwater pollution from nitrates, dissolved organic matter, and detergents was highlighted (1). Urban wastewater is transported over 80 km and distributed by canals for flood irrigation of cropland in a naturally semiarid region, recharging the local aquifer system that pro- vides domestic water for 170,000 people. Irrigation in the Mezquital Valley was 14,000 ha in 1914-1926; 28,000 in 1950; 42,000 in 1965, and 85,000 in 1994 (3). A recharge:discharge ratio of approxi- mately 5:1 has been estimated (4), mani- festing as a rising water table, waterlogging of some fields, and the appearance of new springs and seeps. The region is considered among the most important in Mexico for the area it covers and its economic value from agriculture. Mexico City Metropolitan Zone (MCMZ) wastewater is composed of a mixture of domestic, municipal, and indus- trial wastewater, and stormwater runoff. It receives no conventional treatment (1) and is subject to mixing and natural transforma- tion processes during its transport from the MCMZ to the irrigation region and further biodegradation and sedimentation in a stor- age reservoir. Approximately 55% of the nation's industry is located in the MCMZ (paper, food, chemicals, textiles, and auto- motive), with approximately 43% of the wastewater in the irrigation district of industrial origin, and 57% of domestic and municipal origin (5). The research hypothesis was that pollu- tant levels in groundwater represent a health risk. The research objective was to cost- effectively identify priority risks. Study region The study region is located 80 km north of Mexico City (Figure 1), between the Rivers Tula and Salado, in and around the Endh&o Reservoir. Approximately 10,000 ha receive raw wastewater directly; 35,000 ha receive 80% wastewater + 20% fluvial reservoir water, and 25,000 ha receive naturally treated wastewater from the Requena, Endho, Rojo Gomez, and Vicente Aguirre storage reservoirs (1). The elevation is approximately 1,900 m above sea level, the mean temperature is 17°C, and the mean annual precipitation varies from 700 mm in the southeast to 400 mm in the north (1). Rainy season is pronounced-from June to September. Crops are alfalfa and maize (60%), oats, barley, wheat, beans, and some vegetables-chili peppers, Italian squash, and tomatoes. Cultivation of root veg- etables or those consumed raw is officially prohibited, yet they are grown in some areas. Irrigation is by flooding or furrow, and rates lie between 1,500 and 2,200 mm/ha/year (1). Population. The Mezquital population consists of municipalities of small rural vil- lages that depend on agriculture. In the Tula Jurisdiction (irrigation district 03), 16% of the homes do not have piped water, and 45% must collect water from points outside the home. In addition, only 47% of homes have sanitation (5). Domestic water is rou- tinely collected from groundwater wells and springs. Water is disinfected by small chlori- nation stations that are manually operated and maintained. The areas of focus for the project were the small village of Cerro Colorado, which is adjacent to the spring (population 110) and the area around the spring in the town of Tezontepec de Aldama (population 20,000). Because exposure is a function of socioeconomic conditions, socioeconomic characteristics of a population Address correspondence to Tj. Downs, Environmental Education and Training Institute of North America, Edificio Parque Reforma, Campos Eliseos 400PB, Col. Lomas de Chapultepec, 11000-Mexico, DF, Mexico. Telephone: 52 5 280 4261. Fax: 52 5 280 6774. E-mail: [email protected] Thanks to E. Ruth, X. Ouyang, and G. Bradley (UCLA); C. Hernandez and M. Mazari (UNAM); and I. Gutidrrez, A-M. Tavarez, E. Cruz, and S. Briones in Hidalgo. Financial support was provided by the University of California UCMEXUS Program, the Pan American Health Organization Program for North-South Collaboration in Environmental Epidemiology, and the Mexican Consejo Nacional de Ciencia y Tecnologia (CONACyT). Special thanks to Rob McConnell. Received 29 January 1998; accepted 19 March 1999. Environmental Health Perspectives * Volume 107, Number 7, July 1999 553

Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Embed Size (px)

Citation preview

Page 1: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles

Risk Screening for Exposure to Groundwater Pollution in a WastewaterIrrigation District of the Mexico City RegionTimothy J. Downs,12 Enrique Cifuentes-Garcia,3 and Irwin Mel Suffet1

1Environmental Science and Engineering Program, UCLA School of Public Health, Los Angeles, California, USA; 2lnstituto de Salud,Ambiente y Trabajo, Tlalpan, Mexico City, Mexico; 3Departamento de Salud Ambiental, Instituto Nacional de Salud Publica,Cuernavaca, Morelos, Mexico

Untreated watewater from the Mexico City basin has been used for decades to irrigate croplandin the Mezquital Valley, State of Hidalgo, Mexico. Excess irriion water rechargs the near-sur-fIae aquifer that is used as a domestic water supply source. We assesse the groundwater qualityof three key groundwater sources of domestc water by ng for 24 trace metals, 67 targetbase/neutrlacid (BNA) organic compounds, nontarget BNA organics, 23 chlorinated pesticides,20 polychlorinated biphenyls, and nitrate, as well as microbiological contaminants-coliforms,Vibrio cholerae, and Salmonella Study participants answered a questionnaire that estimatedingestion and dennal exsure to groundwater, 10% of the sample reported frequent diarrheaand 9% reported persistent skin itriations. Detection of V cholerae non-1 in surface waters atall sites suggested a potential risk (surrogate indicator present) of diarrheal dise for canal andriver bathers by accidentl ingestion, as well as potential VI/Prio contamination of near-surfacegroundwater and potential cholera sk m ified by lapses in disinfection. High total coliformlevels in surfae water and lower levels in groundwater at all sites indicated fcal contamiaionand a potential risk of gasointestinal in populations exposed to inadequately disinfectedgroundwater. Using chemical criteria, no significant risk from ingstion or dermal contact wasidentified at the method detection limits at any site, except from nitrate exposure: infants andyoung children are at risk from methemoglobinemia at all sites. Results suggest that pathogenrisk imterventions are a pnonty, whereas nitrate risk needs fiuther characterization to determineif formal treatment is needed. The risks exist inside and outside the irrigation district. Themethod was highly cost-effective. Kq words; groundwater, Mexico, nitrate, pathogens, risk,wastewater irrigation. Environ Healtb Prspect 107:553-561 (1999). [Online 3 June 1999]hap:I/ehpnetl.niehs.nib.gov/docs/1999/107p553-561downs/abstrabhl

Mexico City and the Valley of Mexico indis-putably provides one of the best examples ofa development model in crisis. Of the currentaverage Mexico City wastewater flow of 45m3/sec, approximately 75% is used, withoutformal treatment, to irrigate 90,000 ha in theMezquital Valley, State of Hidalgo (1). Thetotal human exposure implications of thiswater have yet to be explored. The main epi-demiologic research in the region has report-ed significant diarrheal disease and parasiticinfections in farm workers and their families(). In the most recent review of the environ-mental impact of using wastewater for irriga-tion (arguably the largest such region in theworld), the lack of attention to drinkingwater in the zone and potential groundwaterpollution from nitrates, dissolved organicmatter, and detergents was highlighted (1).Urban wastewater is transported over 80 kmand distributed by canals for flood irrigationof cropland in a naturally semiarid region,recharging the local aquifer system that pro-vides domestic water for 170,000 people.Irrigation in the Mezquital Valley was 14,000ha in 1914-1926; 28,000 in 1950; 42,000 in1965, and 85,000 in 1994 (3).A recharge:discharge ratio of approxi-

mately 5:1 has been estimated (4), mani-festing as a rising water table, waterlogging

of some fields, and the appearance of newsprings and seeps. The region is consideredamong the most important in Mexico forthe area it covers and its economic valuefrom agriculture.

Mexico City Metropolitan Zone(MCMZ) wastewater is composed of amixture of domestic, municipal, and indus-trial wastewater, and stormwater runoff. Itreceives no conventional treatment (1) andis subject to mixing and natural transforma-tion processes during its transport from theMCMZ to the irrigation region and furtherbiodegradation and sedimentation in a stor-age reservoir. Approximately 55% of thenation's industry is located in the MCMZ(paper, food, chemicals, textiles, and auto-motive), with approximately 43% of thewastewater in the irrigation district ofindustrial origin, and 57% of domestic andmunicipal origin (5).

The research hypothesis was that pollu-tant levels in groundwater represent a healthrisk. The research objective was to cost-effectively identify priority risks.

Study region The study region is located80 km north of Mexico City (Figure 1),between the Rivers Tula and Salado, in andaround the Endh&o Reservoir. Approximately10,000 ha receive raw wastewater directly;

35,000 ha receive 80% wastewater + 20%fluvial reservoir water, and 25,000 ha receivenaturally treated wastewater from theRequena, Endho, Rojo Gomez, and VicenteAguirre storage reservoirs (1).

The elevation is approximately 1,900 mabove sea level, the mean temperature is 17°C,and the mean annual precipitation varies from700 mm in the southeast to 400 mm in thenorth (1). Rainy season is pronounced-fromJune to September. Crops are alfalfa andmaize (60%), oats, barley, wheat, beans, andsome vegetables-chili peppers, Italiansquash, and tomatoes. Cultivation of root veg-etables or those consumed raw is officiallyprohibited, yet they are grown in some areas.Irrigation is by flooding or furrow, and rateslie between 1,500 and 2,200 mm/ha/year (1).

Population. The Mezquital populationconsists of municipalities of small rural vil-lages that depend on agriculture. In the TulaJurisdiction (irrigation district 03), 16% ofthe homes do not have piped water, and45% must collect water from points outsidethe home. In addition, only 47% of homeshave sanitation (5). Domestic water is rou-tinely collected from groundwater wells andsprings. Water is disinfected by small chlori-nation stations that are manually operatedand maintained. The areas of focus for theproject were the small village of CerroColorado, which is adjacent to the spring(population 110) and the area around thespring in the town of Tezontepec de Aldama(population 20,000). Because exposure is afunction of socioeconomic conditions,socioeconomic characteristics of a population

Address correspondence to Tj. Downs, EnvironmentalEducation and Training Institute of North America,Edificio Parque Reforma, Campos Eliseos 400PB,Col. Lomas de Chapultepec, 11000-Mexico, DF,Mexico. Telephone: 52 5 280 4261. Fax: 52 5 2806774. E-mail: [email protected] to E. Ruth, X. Ouyang, and G. Bradley

(UCLA); C. Hernandez and M. Mazari (UNAM);and I. Gutidrrez, A-M. Tavarez, E. Cruz, and S.Briones in Hidalgo.

Financial support was provided by the University ofCalifornia UCMEXUS Program, the Pan AmericanHealth Organization Program for North-SouthCollaboration in Environmental Epidemiology, andthe Mexican Consejo Nacional de Ciencia yTecnologia (CONACyT). Special thanks to RobMcConnell.Received 29 January 1998; accepted 19 March

1999.

Environmental Health Perspectives * Volume 107, Number 7, July 1999 553

Page 2: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Downs et al.

sample were gathered using a field question-naire. Such a profile is also important for thedesign of appropriate interventions and riskcommunication strategy.

Mortality data from 1995 (6) show thetop five causes of death in the State ofHidalgo (population of2.11 million in 1995)for adults as a) heart diseases (incidence rate61/105); b) cirrhosis and other chronic liverdiseases (46/105); c) malignant tumors(44/105); a) accidents (40/105); and e) dia-betes mellitus (31/105). For infants youngerthan 1 year of age the top five causes were a)perinatal problems (rate 780/105); b) congen-ital anomalies (257/105); c) pneumonia andinfluenza (234/105); ) gastrointestinal infec-tious diseases (101/105); and e) accidents

(48/105). All of these causes of death,except accidents, may be directly or indi-rectly related to environmental pollution.

Water quality assessment. Although inMexico water quality standards are arguablythe most complete in Latin America, institu-tional weaknesses mean they are rarely mon-itored and enforced (7). Growing needs forenvironmentally responsible wastewaterreuse worldwide calls for the inclusion of awider range of parameters that, althoughcurrently unregulated, are potentially toxicas suggested by their structure-activity char-acteristics: the organic fraction of known orpotential toxic and mutagenic effects is thebase/neutral/acid (BNA) fraction (8), suchas polyaromatic hydrocarbons.

The screening parameters consisted of24 trace metals, 67 semivolatile BNA targetorganic compounds [those included indrinking water tests by U.S. EnvironmentalProtection Agency (EPA) methods 525 and625 (9,10)f, nitrate, 23 chlorinated pesti-cides, and a custom 21-congener PCB suite(Table 1).

Criteria pathogens were the bacteriaVibrio cholerae and Salmonella. The V.cholerae enterotoxin produces mild to pro-fuse diarrhea, vomiting, and rapid fluid loss.Morphologically and physiologically similarto V. cholerae 01, the non-01 vibrios pro-duce either cholera toxin (CT) or CT-liketoxin, although the diarrheal illness fromtheir ingestion in contaminated food orwater is milder (11). Only V cholera 01 hasbeen shown to produce cholera (12).Salmonella can cause typhoid and paraty-phoid fever (13), as well as severe diarrheaand dysentery. The indicator organismsused to detect fecal pollution were total col-iforms and Escherichia coli. Total coliformsinclude E. coli, Enterobacter, Klebsiell, andCitrobacter, and are one of the best indica-tors of water treatment effectiveness. Of thefecal coliforms, E. coli is the most reliableindicator because it is specifically of fecalorigin (12).

MethodsExposure assessment. Table 2 shows the con-ceptual matrix used to identify groundwateringestion and dermal contact as local prioritypathways. Exposure was estimated by apply-ing a field questionnaire to 210 families inthe Tezontepec and Cerro Colorado regions.The questionnaire asked specific questionsrelated to ingestion and bathing in the hometo quantify ingestion and dermal contact.Exposure statistics used in the United States(e.g., adult ingestion 2.0 L/day) were notassumed because dimatic and cultural differ-ences between the United States and Mexicowere expected to influence values. Drinkingand bathing habits were captured for two agegroups: 0-15 and 16-70 years of age. Alldrinks and soups containing water were con-sidered, and frequency and duration ofbathing was estimated. This type of ques-tionnaire to quantify exposure had not previ-ously been applied in the region. Living con-ditions and perceptions of water problemswere also captured.

Exposure to contaminants in domesticwater was estimated using the pathwayexposure factor (PEF) method of McKoneand Daniels (14). The relationship betweenrisk and PEF is given in Equation 1. ThePEFs for ingestion and dermal contact arethe exposures per unit contaminant concen-tration for these pathways (Equation 2).The PEFs for ingestion, PEFI, and dermal

Volume 107, Number 7, July 1999 Environmental Health Perspectives

Figure 1. Study region and sampling sites.

.. -!

554

Page 3: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Groundwater risk and wastewater irrigation in Mexico

contact, PEFD, are given by Equations 3and 4, respectively. Additional infant (0-3months) and young children (< 10 kg)groups were used for nitrate exposure. Bodyweight (BW), ingestion (I@, and dermalcontact time (7) statistics were estimatedfrom the population questionnaire. AMonte Carlo method was used to proba-bilistically estimate the PEFs.

R= (CDI- RD) x p [1]

where R = individual risk (unitdess proba-bility); CDI = chronic daily intake of cont-aminant (mg/kg/day); RfD = referencedaily intake (assumed 0 for carcinogens)(mg/kg/day); and p = contaminant toxicityor potency (mg/kg/day)-1.

CDIf = C. x PEF. [2]

where CDIL. = chronic daily intake of cont-aminant by exposure to medium i by path-way j (mg/kg/day); C2 = concentration ofcontaminant in exposure medium i(mg/L); and PEF. = pathway exposure fac-tor by pathwayj (L/kg/day).

PEF = Iwl/BW [3]

where I,IBW= drinking water daily intakeper unit body weight (L/kg/day).

PEFD= TxfxSAIBWx Kp [4]

where T = exposure duration (hr);f = frac-tion of skin surface immersed in contami-nated water (unitless); SA = skin surfacearea (m2); BW= body weight (kg); and K= contaminant permeability constant acrossthe stratum corneum (L/m2/hr).

Skin surface area (SA) was calculatedfrom the relationship published by theInternational Commission on RadiologicalProtection (15), given in Equation 5.

SA = (4BW+ 7)/(BW+ 90) [5]

A value of 10 L/m2/hr for K was usedin Equation 4, following Mckone andDaniels' (14) assumption that the K esti-mate for volatile organic compound's canalso be used as a first-order estimate for thesoluble phase of other waterborne contami-nants. An estimate of 0.6 (± 0.1) for skinfraction (fs) immersed was used for thosewho bathed themselves in groundwatersprings. For those who bathed using cupsor buckets, dermal contact was assumednot to be a significant pathway.

Environmental sampling. Three ground-water sampling locations were chosen(Figure 1). Tezontepec is a rural townapproximately 45 km from the point where

Table 1. Chemical water quality parameters."

BNA target organic compoundsbNameAcenaptheneAcenaphthyleneAnilineAnthraceneAzobenzeneBenzidineBenz(a)anthraceneBenzo(b)fluorantheneBenzo(k)fluorantheneBenzo(g,h,i)peryleneBenzo(a)pyreneBenzoic acidBenzyl alcoholBis-(2-chloroethoxy)methaneBis-(2-chloroethyl)etherBis-(2-ethylhexyl)phthalateBis-(2-chloroisopropyl)ether4-Bromophenyl phenyl etherButylbenzyl phthalateChrysene4-Chloroaniline4-Chloro-3-methylphenol2-Chlorophenol4-Chlorophenyl-phenyl etherDibenzo(a,h)anthraceneDibenzofuran1 ,2-Dichlorobenzene1 ,3-Dichlorobenzene1 ,4-Dichlorobenzene3,3'-Dichlorobenzidine2,4-DichlorophenolDiethyl phthalate2,4-DimethylphenolDimethyl phthalateDi-n-butyl phthalate2,4-Dinitrophenol2,4-Dinitrotoluene2,6-DinitrotolueneDi-rnoctyl phthalateFluorantheneFluoreneHexachlorobenzeneHexachlorobutadieneHexachlorocyclopentadieneHexachloroethanelndeno(1 ,2,3,4-c,d)pyreneIsophorone2-Methyinapthalene2-Methyl-4,6-dinitrophenol2-Methylphenol4-MethylphenolNapthalene2-Nitroaniline3-Nitroaniline4-NitroanilineNitrobenzene2-Nitrophenol4-NitrophenolN-NitrosodimethylamineN-NitrosodiphenylamineN-Nitrosodi-n-propylaminePentachlorophenolPhenanthrenePyrenePhenol2,4,5-Trichlorophenol2,4,6-Trichlorophenol

MDL0.060.062.10.070.06

510.060.140.150.370.074.000.810.330.350.050.080.620.300.071.30.550.330.350.40.060.080.080.081.30.610.060.40.060.064.11.21.20.060.060.060.60.792.40.170.370.120.122.70.440.490.071.20.941.30.670.646.20.830.210.333.10.060.071.52.10.58

MetalscName

AluminumArsenicBariumBerylliumBoronCadmiumCalciumChromiumCobaltCopperIronLanthanumLeadMagnesiumManganeseMolybdenumNickelPotassiumSeleniumSiliconSodiumStrontiumVanadiumZinc

MDL147.23.70.3

510.99

3.2

1.44.75.41.3

2.2

12

40.8

Chlorinatedpesticidesd

name

2,4'-DDE4,4'-DDD4,4'-DDE4,4'-DOTa-BHCa-ChlordaneAldrinP-BHCcis-ChlordaneD-BHCDDD + endrinaldehyde

DieldrinEndosulfan sulfateEndosulfan 1Endosulfan 2EndrinEndrin aldehyde'tBHC.tChlordaneHeptachlorHeptachlorepoxide

MethoxychlorMirex

PCBsdnameBZ 8BZ 18BZ 28BZ 44BZ 52BZ 66BZ 77BZ101BZ 105BZ 118BZ 126

BZ 128BZ 138BZ 153BZ 155BZ 170BZ 180BZ 195BZ 206DCB

T-Nonachlor

Abbreviations: BHC, benzenehexachloride (isomers); BZ, Ballschmiter-Zell classification of 209 PCB congeners; MDL,method detection limit in pg/L (ppb).'Except nitrate [standard method 4110C (18)]. bU.S. EPA methods 525 (drinking water) (9), 625 (wastewater) (10).'Standard method 3120B (18). 0J.S. EPA method 608 (19).

Environmental Health Perspectives * Volume 107, Number 7, July 1999 555

Page 4: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Downs et al.

the wastewater enters Hidalgo. It has a localspring (site TZG) derived from the infiltra-tion of irrigation water. Cerro Colorado isthe main spring in the valley, supplyingdomestic water to 170,000 people (Table3). The spring (site CCG) is approximately35 km from the wastewater entry and wasthe second sampling location. The thirdlocation was a natural spring derived fromupland precipitation approximately 8 kmfrom the wastewater entry. This site (ESG)near the River El Salto was the control sitefor near-surface groundwater quality andwas a natural near-surface aquifer dis-charge point located outside the irrigationdistrict. Because groundwater in the valleyis either of the wastewater-derived near-surface aquifer or the deeper (50-100 m)hydrothermal aquifer, it was important tocarefully choose a control for the near-surface aquifer.

Each sample set included one sample formetals, one for organics, and one forpathogens. Four sets of samples of ground-water were taken at each site once per monthduring the dry season, when dilution of con-taminant concentrations was expected to belowest (December 1996-March 1997).Samples of adjacent surface water were alsotaken for pathogens. Samples from a housetap at Tezontepec (site TZH) were takenonly once. The sampling regime was consid-ered optimal for the resource constraints,although some samples were lost in transit.

Microbiological testing. Water sampleswere collected in 200-mL plastic containersfor microbiological testing at each site and atsurface water sites adjacent to the groundwa-ter sites (TZS, CCS, and ESS). Biochemicaldeterminations of the presence/absence ofV cholerae and Salmonella were carried outat the State Public Health Laboratory(Hidalgo). Results of suspected positiveswere sent to the National Institute ofEpidemiological Diagnosis and Reference(Santo Tomas, Mexico City, Mexico) forpolymerase chain reaction confirmation. Asemiportable device for quantitatively mea-suring total and E. coli levels, AutoanalysisColilert (Idexx Laboratory, Inc., Westbrook,ME), was used on one sampling day. Thismethod is also called the minimal mediamethod (15).

Physicochemical and chemical testing.Physicochemical parameters-temperature,pH, dissolved oxygen, and conductivity-were measured in the field using portablemonitors from Yellow Springs InstrumentCompany, Inc., Yellow Springs, Ohio. Ateach sampling point, amber glass bottleswith Teflon (E.I. Du Pont de Nemours andCo., Wilmington, DE) caps were used totake 1 L of water for metals analysis and 1 Lfor organics analysis. Travel blanks consisted

Table 2. Conceptual matrix of exposure pathways.Medium i/Pathwayj Airp Airg SW GW Soil Sed BiotaInhalation ell e21 e31 e41 e51 - -

Ingestion e12 e22 e32 e42 e52 e62 e72YDermal contact e13 e23 e33 e43 e53 e63

Abbreviations: Airg, air gases; Airp, air particles; eij, possible route; eij, expected Mezquital route; eij, study focus; GW,groundwater; Sed, sediment; SW, surface water.81n Mezquital: crops, bioconcentration of lipophylic organic compounds in milk, beef, and sheep's meat.

Table 3. Domestic water supply from Cerro Colorado spring.

Aqueduct NS People Flow (L/sec) L Type DisinfectionCerro Colorado 7 135,000 200 36 Gravity ChlorinationC. Colorado-Huitel 23 35,000 130 7.5 Gravity ChlorinationTotal 30 170,000 330 43.5 - -

Abbreviations: L, length (km); NS, number of settlements supplied. Data from Comisi6n Nacional del Agua (16).

of 1 L water purified using a Millipore com-plete purification system (Millipore Corp.,Bedford, MA), consisting of reverse osmosisand reagent grade purification. Sampleswere kept in ice and shipped by expresscourier for next day delivery to theUniversity of California, Los Angeles (LosAngeles, CA) laboratory.

Nitrate levels in water were determinedby standard method 41 10C (18). Simultane-ous metals analysis of the filtered aqueousphase was carried out by standard method3 120B (18), an inductively-coupled plasma/atomic emission (ICP/AE) method, on aPerkin-Elmer Optima 3000 DA ICP-AESSpectrometer (Perkin-Elmer, Norwalk,CT). Water samples were analyzed for EPAtarget drinking water BNA contaminantsusing an expanded list of analytes, based onEPA Methods 525 (drinking water) (9-) and625 (wastewater) (10). Method 625 wasmodified using a capillary column. Methoddetection limits are given in Table 1.Samples were analyzed for chlorinated pes-ticides and PCBs using methods based onEPA method 608, Pesticides and PCBs[polychlorinated biphenyls] (19).

Semivolatile BNA compound, organo-chlorine pesticide, and PCB analyses werecarried out by concentrating the watersample using standard method 3520A(Liquid-Liquid Extraction) (18). Theextraction used a 1-L sample for metalsanalysis and 1 L for BNA. A batch extrac-tor was used with dichloromethane as theactive agent. Samples were dried on a sodi-um sulfate column, concentrated to 1 mLby Kuderna-Danish evaporation, and ana-lyzed with a Finnigan 4000 (Finnigan, SanJose, CA) gas chromatography/mass spec-trometer (GC/MS). The GC column was aDB-5MS, 30 m x 0.25 mm. Six internalstandards were injected into the sample at 40ng/pL before GC/MS analysis. These stan-dards were 1,4-dichlorobenzene-D4, naptha-lene-D8, acenapthene-D10, phenanthrene-D10, chrysene-D12, and perylene-D12.

Chlorinated pesticides and the selectedPCB suite analyses were carried out usingGC/electron capture detection (ECD) on aVarian 3500 instrument (Varian, WalnutCreek, CA) and dual columns. Methoddetection limits for aqueous samples ofPCBs and chlorinated pesticides were0.005-0.010 pg/L.

BNA organic analysis included distin-guishing and approximately quantifyingnontarget trace organics, using GC/MSprofiling (20,21). Nontarget compoundswere tentatively identified when possible byvisually inspecting sample spectra and com-paring them against closest matches fromthe 42,000-compound EPA/NationalInstitutes of Health Mass Spectral DatabaseLibrary (22). Because response factors wereunknown for nontarget compounds, eachcompound's concentration was approxi-mately quantified by comparing ratios of itsspectral area to the spectral area of the clos-est internal standard of known concentra-tion. Each compound has a specific scannumber from the GC total ion current,which is mainly a function of molecularweight (MW) and boiling point (BP). TheGC/MS output total ion chromatogramswere cleaned of peaks found in travel blanksand phthalates known to be experimentalartifacts. A list of target and tentativelyidentified nontarget compounds was com-piled for each sample for data comparison.

Results and DiscussionSocioeconomic population profile. Using thequestionnaire results, the sampled popula-tion of 210 families was characterized byeducation level, living conditions, bathinghabits, drinking habits, and health signs(Table 4). The illiteracy rate was 10% inmale heads of the family and 14% in moth-ers. Most houses had cement floors (89%)and water closets (inside 30%, outside 46%).The percentage of families without drainagewas 17%; without piped water, 1 1o%.Springs were popular bathing places (39% of

Volume 107, Number 7, July 1999 * Environmental Health Perspectives556

Page 5: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Groundwater risk and wastewater irrigation in Mexico

Table 4. Socioeconomic population profile.a

Characteristic %b

1.1 Age of head of family 2030 years 221.2 Age of head of family 30-40 years 241.3 Age of head of family 60-70 years 152 Education2.1 Family head reads and writes 892.2 Family head neither reads nor writes 102.3 Mother reads and writes 832.4 Mother neither reads nor writes 142.5 Family head did finish primary school 292.6 Family head did not finish primary school 372.7 Family head did finish secondary school 123 Living conditions3.1 House floor is cement 893.2 House floor is earth 63.3 House roof is tin 313.4 House roof is cement 683.5 House roof is cardboard 23.6 House has WC inside 303.7 House has WC outside 463.8 House has no WC 243.9 House has waste drainage 743.10 House has septic tank 83.1 House has no sanitaion 173.1 House has piped water inside 273.1 House has piped water outside 623.1 House has no piped water 114 Bathing habits4.1 Family bathes inside with shower 254.2 Family bathes with small bowl 294.3 Family bathes in spring 395 Drinking habits5.1 Drinking water from tap 2852 Drinking water from spring 655.3 Drinking bottled water 45.4 Boil water> 10 min before drinking 245.5 Boil water < 10 min before drinking 75.6 Do nothing to water before drinking 656 Health signs6.1 Frequent diarrhea among family 106.2 Persistent skin irritations 9

WC, water closet'n = 210 families; important exposure data in bold.bPercentage of sampled families wiffi characteristic.

families) and sources of drinking water(65%). Most families did not sterilize theirdrinking water (65%), and only 4% usedbottled water. Ten percent of families report-ed frequent diarrhea. Nine percent reportedpersistent skin irritations, which could beeffects of dermal contact with wastewater.Almost all families questioned stated that themain advantage of treating wastewatersbefore irrigation would be "deaner crops."

Observations of barefoot farm workers,children bathing in canals, and livestockingesting wastewater suggest human dermalexposure to wastewater (e33, Table 2) andingestion (e72, Table 2) of the food productsof animals exposed to wastewater should beassessed-cow's and goat's milk, beef, andsheep's meat.

Groundwater pathway exposure factors.The children's mean groundwater ingestionwas 1.6 ± 0.48 L/day [standard deviation

(SD)], and the adult mean was 2.0 ± 0.45L/day (Table 5). Mean dermal contacttimes (± SD) for children and adults were11 ± 3.6 and 11 ± 3.3 min/day, respective-ly. The mean PEFs (± SDs) for ingestionfor children and adults were 0.092 ± 0.076and 0.033 ± 0.010 L/kg/day, respectively(Table 6). The mean PEFs (± SDs) for der-mal contact for children and adults were0.035 ± 0.017 and 0.024 ± 0.010 L/kg/day,respectively. In children, the ingestion rate(I,@ contributed 70% of the uncertainty inthe ingestion PEF and BW 30%, whereasfor dermal contact 54% of the uncertaintywas accounted for by uncertainty in con-tact time (T) and 31% by skin fractionimmersed (f). For adults, the ingestionrate contributed 66% of the uncertainty inthe ingestion PEF and BW 34%, whereasfor dermal contact 55% of the uncertaintywas accounted for by uncertainty in con-tact time and 34% by skin fractionimmersed.

Microbiological indicators. Of theMarch 1997 surface water samples TZS,CCS, and ESS (adjacent to the ground-water sites TZG, CCG, and ESG), only theTZS sample was positive for the V choleraeserogroup non-01. All surface water sitesamples taken in December 1996 were pos-itive for V cholerae non-01. Samples takenin December 1996 were negative forSalmonell at all sites. The March 1997 col-iform counts were greater than the instru-ment maximum > 2,419/100 mL) for totalcoliforms and E. coli in all surface watersites. The March 1997 groundwater sam-ples TZG, CCG, and ESG registered totalcoliforms at 770; 1,730; and 37/100 mL,respectively, and E. coli at 7, 4, and 0/100mL, respectively. The March 1997 housesample (TZH) had values of 0 for totalcoliforms and E. coli.

The presence of V cholerae-non 01 inall surface water sites is a red flag; the near-surface groundwater supplies are potential-ly at risk from contamination, with a resul-tant potential cholera risk. Because thisbacterium is almost exdusively transmittedby water (13), prevention of epidemiccholera depends on providing a safe drink-ing water supply that is chlorinated andfree from sewage contamination; lapses indisinfection that occur during the manualchangeover of chlorine tanks magnifies therisk. Coliform counts suggest a potentialrisk of gastrointestinal diseases at all sites,with total coliforms and E. coli countsabove the Mexican standard (23) of 2/100mL and 0/100 mL, respectively. WorldHealth Organization (WHO) guidelines(12) for fecal coliforms in drinking waterwere exceeded (includes E. coli), as were theWHO guidelines (24) for wastewater reuse

for the irrigation of crops likely to be eatenuncooked-limits for fecal coliforms were< 1,000 per 100 mL (geometric mean).Unlike studies with wastewater reservoirsin Israel, where fecal coliforms are removedby up to five orders of magnitude afterretention (25), the comparison of the sitebefore retention in the Endho Reservoir(Figure 1, ESG/ESS) with the site afterretention (TZG/TZS) did not show thiseffect. This may be because the Tula Riverreceives fecal pollution after retention,along the 20 km between the reservoir andthe sampling site.

Nitrate data. Table 7 shows means andSDs of nitrate ion concentration (NO3-).Mean nitrate in groundwater ranged from47 to 69 mg/L, whereas the health standardis 50 mg/L. The single sample at the house(TZH) was highest at 73 mg/L. ESG (con-trol site) nitrate levels of 47 mg/L are notattributable to wastewater infiltration:manure from grazing cattle -and horses, andfertilizers are likely sources. Using PEF) val-ues from Table 6, mean CDI for the chil-dren ranged from 4.3 mg NO3-/kg/day atESG to 6.3 mg NO3i/kg/day at CCG. TheTZH value was 6.7 mg N03/kg/day.Corresponding values for the adult groupwere 36% of the child values. Assuming arisk group of young children of BW 10 kgand ingestion 1 L/day (PEF1= 0.1 L/kg/day),the CDI ranges from 4.7 mg NO3i/kg/day atESG to 6.9 mg N03i/kg/day at CCG. Forthe highest risk group of infants assuming aBW of 4 kg and ingestion of 0.6 L/day(20) PEF,on the order of 0.15 L/kg/day-the CDI ranges from 7 mg NO3i/kg/day atESG to 10 mg NO 1lkg/day at CCG.

In infants, t1e drinking water noobserved adverse effect level (NOAEL) andlowest observed adverse effect level(LOAEL) for methemoglobinemia havebeen given in dose terms as 1.6 mg nitrate-nitrogen/kg/day and 1.8-3.2 mg/kg/day,respectively (26,27), equivalent to approxi-mately 7 mg NO3/kg/day and 8-14 mgNO3ikg/day. The NOAEL is also the oralreference dose (oral RfD) in equation 1(uncertainty factor of 1). The infant groupis at risk at all sites because CDI 2 RfD.Using the acceptable daily intake (ADI) of3.65 mg NO3/kg/day, young children ofBW < 10 kg and ingestion 2 1.0 L/day arealso at risk because CDI 2 ADI. In methe-moglobinemia, nitrate reduced to nitriteoxidizes hemoglobin to methemoglobin,impairing oxygen transport to tissues.Although experiments with animals suggestneither nitrate nor nitrite acts directly as acarcinogen, it may increase cancer risk inhumans by endogenous formation of N-nitroso compounds whereas evidence impli-cating high nitrate in drinking water with

Environmental Health Perspectives * Volume 107, Number 7, July 1999 557

Page 6: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Downs et al.

other end points such as congenital malfor-mations, cardiovascular effects, and thyroideffects are inconclusive (12).

Physicochemical data. Table 7 showsmeans and standard deviations of tempera-ture at site (7), site pH, conductivity (C),dissolved oxygen (DO). Mean T wasapproximately 20°C, with pH rangingfrom 7.1 to 7.6. Conductivity ranged from1,200 to 1,850 pmhos (TZH) and DObetween 5.2 and 6.9 mg/L, with coeffi-cients of variation at CCG and ESG of0.45 and 0.23, respectively.

Metals, BNA organics, chlorinatedpesti-cides, and PCBs. Mean levels of the 24 tar-get heavy metals did not exceed U.S. SafeDrinking Water Act (29-) maximum conta-minant levels and maximum-level goals orMexican standards (23) at any site; there-fore, no significant risk was identified bythese criteria (Table 8). No target BNAorganics were detected in the samples; there-fore, no significant risk was identified bythese criteria at the method detection limit,whereas several nontarget BNA compoundswere detected in samples, most of whichcould not be identified (Table 9). The num-ber of tentatively identified compounds inthe sampled groundwater ranged from 0(ESG) to 2 (CCG), and unidentified com-pounds from 2 (TZG) to 9 (CCG). All ten-tatively identified compound levels were < 2pg/L, and all detected compounds were < 6pg/L. Tentatively identified and unidenti-fied compounds are of unknown but poten-tial toxicity, so an unknown risk exists bythis criterion.

Only one chlorinated pesticide wasdetected from the list, 'y-chlordane in ESG,on 12 March 1997 at approximately 30pg/L (on the order of 10`11 g/L). There isno evidence this compound is a human car-cinogen (31). Levels in water in previousstudies in Hawaii (32) were on the order of1 ng/L, and levels of magnitude 10-11 g/Lare considered low. Therefore, risk by thispollutant was considered insignificant.

Several PCB congeners were detectedfrom the PCB list (Tables 1 and 9). Themain transport medium is air, with strongsorption to suspended particles and soil. Forthis reason, leaching is limited and ground-water levels low (33). PCBs are classified assuspected carcinogens by the EPA on thebasis of animal tests. They have a potentialto cause developmental and fetotoxic effectsin humans, and there is evidence that theymay cause hepatoxicity (34). However,typical levels between 0.1 and 0.5 ng/Lfound elsewhere in drinking water representnegligible contributions to body burden ascompared to food intake (35). For thesereasons, the low levels detected (< 36 pg/L)were not considered a risk factor. Tables 10

Table 5. Ingestion and dermal contact statistics.

Groundwater volume ingested (LI DermalAge group BW vl v2 v3 v4 v5 v6 vT T0-1 5 yearsAvg 22.6 1.02 0.11 0.17 0.02 0.14 0.16 1.62 10.8SD 114 0.39 0.08 0.19 0.05 0.06 0.05 0.48 3.6nai 103b 161 161 161 161 161 161 161 113b

16-70 yearsAvg 63.4 1.37 0.11 0.22 0.02 013 0.16 2.02 10.8SD 10.1 0.35 0.10 0.18 0.05 0.06 0.09 0.45 3.3r/c 134b 210 210 210 210 210 210 210 150b

Abbreviations: Avg, sample average; BW, body weight (kg); n, sample size; SD, sample standard deviation; T, daily dermalcontact time (min/day) from bathing in springs; vl, water volume (liters) consumed from plain water drink; v2, flavoredwater drinks; v3, coffee and/or tea; v4, atole corn drink with water; v5, soup or broth; v6, stew; vT, total volume (liters).aNumber of families with children in that group. bSample size in age group. cNumber of families.

Table 6. Pathway exposure factor statistics.

Children 0-15 years of age Adults 16-70 years of agePEF, PEF0 PEF, PEF0

StatisticMean 0.092 0.035 0.033 0.024Median 0.070 0.034 0.032 0.023Mode 0.057 0.034 0.030 0.017Standard deviation 0.076 0.017 0.010 0.010

SensitivityaIngestion (nb 70 _ 66Body weight (BM 30 10 34 3Bathing time () - 54 - 55Skin fraction (f) 31 35Permeability (Kp) 5 7

Abbreviations: PEFD, pathway exposure factor for dermal contact (L/kg/day); PEF,, pathway exposure factor for ingestion(L/kg/day).TPercent contributions to pathway exposure factor variance. bSee Equations 3 and 4.

and 11 summarize chemical and microbio-logical health risks, respectively, identifiedat method detection limits.

Removalprocesses. The chemical conta-minant levels in near-surface groundwaterwere lower than expected considering theshort infiltration depth of a few meters forraw wastewater. However, because the sam-pling sites are springs, the water has alsobeen subject to horizontal groundwaterflow over distances up to several tens ofkilometers. Degradation and dispersionprocesses, organic sorption to soil and trap-ping of suspended solids, and EndhoReservoir retention (Figure 1) appear toeffectively remove BNA organic contami-nants. During the 80-100 km journey ofwastewater from Mexico City to theIrrigation District, it is likely that metals andorganics associated with suspended mattersettle out, whereas the soluble fractions ofmetals and organics sorb to bottom sedi-ments and soils during infiltration.Biodegradation of xenobiotics is probablyactive in the canals, reservoir, and soil (36).Despite the apparent efficiency of naturaltreatment processes, if the water table contin-ues to rise and fields become saturated (4),the bioavailability of wastewater-borne cont-aminants will increase, creating differentexposure conditions. This is one argument

for reducing the incoming wastewater flowfrom Mexico City, and this would also freeup the wastewater for recycling within theMexico City basin, where water is scarce.Using cleaner local groundwater and moreefficient irrigation would reduce environ-mental health impacts and allow highervalue crops to be grown.

Direct exposure to surface wastewaterthrough inhalation and dermal contact, andindirectly through ingestion of milk, beef,sheep's meat, and crops may be importantand should be evaluated: Dairy cattle andsheep drink directly from sewage canalsbecause no other surface water is available.

Conclusions andRecommendationsRisks. Our results suggest that pathogens arepriority agents as compared to chemicals forgroundwater ingestion, and they are notrestricted to the wastewater irrigation district.By the coliform criterion, a potential risk ofgastrointestinal disease was identified withtotal coliforms and E coli counts above theMexican standard (23), particularly becausedisinfection can be intermittent when chlo-rine tanks run dry and changeover is not effi-cient. No risk by Salmonella was identified.The presence of V cholerae non-0 1 in surfacewaters including the river (TZS) indicates a

Volume 107, Number 7, July 1999 * Environmental Health Perspectives558

Page 7: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Groundwater risk and wastewater irrigation in Mexico

Table 7. Nitrate and physicochemical field data.

NO3- (mg/L) Conductivity (pmhos/cm) Dissolved oxygen (mg/L) Temperature ()C) pHSite M SD CV n M SD CV n M SD CV n M SD CV n M SD CV nBlank ND ND ND - 46 17 0.4 3 - - - - - - - - NM NM NMTZG 61 2 0.0 3 1,780 66 0.0 3 6.1 0.7 0.1 3 21.4 0.1 0.0 3 7.4 0.3 0.04 3CCG 69 1 0.0 4 1,630 550 0.3 3 5.7 2.6 0.4 3 19.7 0.4 0.0 3 7.1 0.2 0.03 3ESGa 47 7 0.2 4 1,230 360 0.3 3 6.9 1.6 0.2 3 20.8 0.4 0.0 3 7.6 0.4 0.05 3TZH (73) - - 1 (1,850) - - 1 5.2 0.6 0.1 2 19.7 0.2 0.0 3 (7.1) - - 1Abbreviations: CCG, Cerro Colorado River groundwater site; CV, coefficient of variation; ESG, El Salto River groundwater site; M, mean; n, number of samples; ND, not detected; NM, notmeasured; SD, standard deviation; TZG, Tezontepec de Aldama groundwater site; TZH, Tezontepec de Aldama house site. Single sample values are denoted by parentheses.'Control site-zero wastewater influence.

Table & Metals levels in groundwater (pg/L) (aqueous phase, solid phase negligible).

Standards Blanks Groundwater levelsMetal Mex MCLG MCL MDL Bm Bsd ESGm ESGsd EX? TZGm TZGsd EX? TZH EX? CCGm CCGsd EX?Aluminum 200 N/E N/E 14 N - - N - N - - N

A: W-'WA:: i'fll.w - - :-.2; N;$:;12 3....... .. ..Nc. 15 N.,.S I.w..N-Barum 700 2,000 2,000 3.7 - - 81 3 N 78 2 N 100 N 99 9 N

Boron t1,0t40 - 10 51 241 324 280 0 N 753 29 N 810 N 787 72 Ne9.V; t~~~~~~~~~~~~~~~---Sn....... . .; . N vCalcium - N/E N/E - 9 1 49,000 1,730 - 73,000 3,220 - 78,000 - 91,000 1,160ii:%..n- 3 - - - ;^ '' N : -N

It -N/E N/E N

Iron 300 N/E N/E 4.7 N - - N 10 N - - NflTh, -eg ,- ........................................... ;. ... ..

Leada 25 0 15 1.3 N - - N - N - - N1,160Manganese 150 - 200 - 130 - N 1 N N 2 1 N

1. ^

Nickei HA . ) 1 0 N N10- N--Selenium - 50 50 12 W N - ZNN- - - 3 - NSX~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ........ s 3 -Sodium 200,000 N/E N/E - 241 13 86,000 7,550 N 170,000 14,900 N 200,000 N 193,000 11,600 N-

Vanadium - N/E N/E 4.0 - - 31 1 - 33 2 - 26 - 29 6

Abbreiations: anayt not detcbted; Bm, blank mean; Bsd, blank SD; CC6m, Cerro Colorado River groundwater site mean (n 3); CCGsd, Carro Colordo Rivr groundwater site SD (n= 31; ESDm, El Salto River groundwater site mean; ESGsd, El Saloe River groundwater site SD; EX?, exceeds standards?; MCL maximum contaminant levl allowed in U.S. drinking water,MCLG, maximum contaminant level goal of the U.S. Safe Drinking Water Act [date from Pontus IS!l; MDL mnetod detection limit (pg/L or ppb); Max, Mexican standard (23); N, no (nei-ther U.S. nor Mexican standards exceeded); NIA, not applicable; NWE, not established; SD, standard deviation; TT, treatnent-technique dependent TZGm, Tezontopec de Aldamagroundwater site mean; TZH, Tezontepec de AJdama groundwater house site; TZ6sd, Tezontepec de Aldama groundwater site SD. Anaysis by standard method 31206 (19. MDL must be< standard.In the ATSDMU.S. EPA top 20 hazardous substances prority listfor 1997 (30. llexavalent

potential risk of diarrheal disease for peoplebathing and accidentally ingesting this water.A potential risk of cholera exists because ofpossible near-surface groundwater contami-nation by Vibrio in surface water, a riskincreased by lapses in chlorination. Ten per-cent of families of the sample populationreported frequent diarrhea.

By the nitrate criterion, the infant andyoung children groups are at risk frommethemoglobinemia at all sites and are notrestricted to the wastewater irrigation dis-trict. This risk warrants further characteriza-tion that includes a focused epidemiologicstudy before the investment of scarceresources in source control and/or treat-ment technology can be justified. Anyfuture treatment should be appropriate forthe rural context. No risk was identifiedusing the metals criteria at method detection

limits. By the criteria of BNA target com-pounds, chlorinated pesticides, and PCBs,no significant risk was identified at methoddetection limits. An unknown risk existsfrom tentatively identified and unidentifiedBNA compounds, although all detectedcompounds were at levels < 6 pg/L. Ninepercent of the sample reported persistentskin irritations, which could be effects ofdermal contact with wastewater chemicalsin canals and fields.

The screening method proved cost-effec-tive in identifying priority risks in a complexpollution situation, a valuable tool in thesearch for health interventions that are effi-cient. The screening method is less costlythan traditional epidemiologic studies andorients such studies, an approach particularlyappropriate in less-developed countrieswhere resources are scarce.

Potential treatment options. Micro-biological risk agents require better control,with improvements sought for manualchlorination, such as low tank and irregulardose warnings, systematic tank replacement,better operator training, and/or simpleautomated, low-cost systems. Major plansto treat the wastewater leaving Mexico Cityand entering Mezquital are under review,with large-scale primary treatment and dis-infection targeted at pathogen removal (4.Major treatment/disinfection optionsrequire full cost-effectiveness and impactassessment, and an understanding of theresistances of different pathogens, not merelyconsideration of the most studied risk fromhelminth eggs (1). However, even withmajor treatment, local pathogen risk sourceswould still need attention by improvingbasic hygiene and low-cost rural sanitation.

Environmental Health Perspectives * Volume 107, Number 7, July 1999 559

Page 8: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Downs et al.

Table 9. BNA organics, chlorinated pesticides, and polychlorinated biphenyl data.

Parameter/site ESG ESG TZG TZG CCG CCGBefore/after reservoir retention? Before Before After After - -1997 sampling date 10 Jan 12 Mar 10 Jan 12 Mar 10 Jan 12 Mar

BNA organic compoundsNumber of target compounds 0 0 0 0 0 0Mass targets (%) 0 0 0 0 0 0Number of nontarget compounds 6 3 3 3 6 11Number tentatively identified 1 0 1 0 1 2Number unidentified 5 3 2 3 5 9Mass nontargets (%) 100 100 100 100 100 100

Estimated amounts (pg/L)Nontarget compounds (tentatively identified)aCyclotrisiloxane, hexamethyl- 1 - 2 - 1 -

propanoic acid, 2-methylbutyl ester - - - - - 21-dodecyne - - - - - 1

Chlorinated pesticides (pg/L)y-Chlordane - 30 - -

Polychlorinated biphenyls (pg/L)BZ 28 - - - - - 11BZ66 26 - 20 16 10 36T-Nonachlor 4 - 19 - 11 -

BZ 105 2 - - 6 - -BZ 153 - - 36 - - -BZ 180 14 25 35 - 22 7BZ 187 6 - 13 - - 4

Abbreviations: BNA, base/neutral/acid; BZ, Ballschmiter-Zell classification of 209 PCB congeners; CCG, Cerro ColoradoRiver groundwater site; ESG, El Salto River groundwater site; TZG, Tezontepec de Aldama groundwater site.aScan numbers 496; 1,392; and 2,059, respectively.

Table 10. Summary of chemical risks (at method detection limits).

Parameter No. Level Risk

Target BNA organics 0 0 NoNontarget BNA organics 3-11 . 2 pg/L ?Chlorinated pesticides 1 30 pg/L NoPolychlorinated biphenyls 2-5 < 36 pg/L NoNitrate - 7-10 mg/kg/day,a > 3.65 mg/kg/dayb YescTrace metals < drinking water standard No

Abbreviations: ?, unknown risk; ADI, acceptable daily intake; BNA, base/neutral/acid; CDI, chronic daily intake; No., num-ber of compounds detected. Determinations of risk apply to all sampling sites Tezontepec de Aldama, Cerro ColoradoRiver inside wastewater irrigation district, and El Salto River outside.alnfant group CDI. bYoung children CDI. cMethemoglobinemia risk in infants (CDI 2 reference dose) and young children(CDI > ADI).

Table 11. Summary of microbiological risks (atmethod detection limits).

Parameter Presence Risk

Vibrio cholerae V cholerae non-01 Potential8 choleraSalmonella None NoTotal coliforms 37-770/1 00 mL Potentiala Gl diseaseE coli 0-7/1 00 mL Potentiala G0 disease

Gl, gastrointestinal.Determinations of risk apply to all sampling sitesTezontepec de Aldama, Cerro Colorado River inside waste-water irrigation district, and El Salto River outside.ai.e., surrogate indicators of risk agent detected.

If further risk characterization provesnitrate management is needed, source iden-tification and control should be the prima-ry techniques. If control is impractical, lowmaintenance, village-scale denitrification ofrural groundwater supplies would beappropriate. Such a method has beendemonstrated by Silverstein et al. (37)using a novel packed tower biofilm reactorto a removal efficiency of 80-90% with

influent flow at 38 L/min, 88-110 mg/LNO3-. Noyola and Morgan (38) in Mexicodesigned an anaerobic-anoxic-aerobicprocess to eliminate organic matter andnitrate in municipal and domestic waste-waters. When organic matter is low, as inMezquital influent, the first-stage anaero-bic-activated sludge reactor is excluded,which leaves two main components: ananoxic activated sludge denitrifier withupward flow, and a packed nitrifier, withrecirculation between the two. For theMezquital conditions, a second, smallerdenitrifier can be placed after the first, inwhich methanol is dosed stochiometricallyas the external carbon source. This methodcan achieve 95% removal of total nitrogenfor flows on the order of 1.5 L/sec.

Institutional and educational interven-tions. Pathogen risks should be mitigatedby a vigorous campaign that encourageshand-washing after defecation and before

preparing and eating meals, and the boilingof drinking water from springs. Nitrate riskshould be mitigated by breast-feedinginfants instead of using water-based formu-la, and the consumption of low cost, certi-fied purified water (an l 8-L container costs$6.00 to purchase and half a field worker'sdaily wage to renew-$1.50). In developedcountries, treatment plants would beinstalled to mitigate risk, but because physi-cal intervention is often deemed too costlyand is slow to appear in poor, rural commu-nities of developing countries, active insti-tutional and educational intervention tocombat the nitrate and microbiological risksmust precede it-and often substitute it.This should be a collaboration betweenpublic health officials (the local SanitaryJurisdiction in Tula and the State PublicHealth Office in Pachuca), communityleaders, and water resource agencies (localutility companies and the state-levelNational Water Commission, CNA-Hidalgo). Public health officials need toeffect a more persistent campaign of riskcommunication with basic hygiene educa-tion that is culturally accepted, whereas thewater resource agencies need to work moreclosely with researchers to design and helpinstall sanitation that is economically andtechnically feasible for the rural, agriculturalcontext of Mezquital. Environmentalhealth problems are slowly beginning tofuel much-needed multidisciplinary collab-oration at the technical level, but inter-institutional collaboration, communityparticipation, and the transfer of knowl-edge into cost-effective solutions to priorityproblems are still the major challenges inMexico-collective responsibilities forhealth professionals, engineers, and politi-cians to assume.

Research recommendations. Appliedresearch should first address priority inter-ventions for pathogen risks. Secondary topicsinclude a fuller characterization of nitraterisk-an adequate, focused case-controlepidemiologic study using a new controlsite exposed to low nitrate; improved sur-veillance (any infant death from methemo-globinemia is presently unidentified inlocal health records); direct and indirecthuman exposure to wastewater in canalsand flooded fields, especially dermal con-tact for bathing children and barefootfarmworkers; and indirect human exposureby ingestion of crops, cow's milk, beef, andsheep's meat.

REFERENCES AND NOTES

1. Siebe C, Cifuentes E. Environmental impact of waste-water irrigation in central Mexico: an overview. Int JHealth Res 5:161-173 (1995).

2. Cifuentes E, Blumenthal U, Ruiz-Palacios G, Bennett

560 Volume 107, Number 7, July 1999 * Environmental Health Perspectives

Page 9: Screening Exposure to Groundwater Pollution Wastewater ... · PDF fileRiskScreeningfor ExposuretoGroundwaterPollution in aWastewater ... industrial origin, ... the mostcompletein LatinAmerica,

Articles * Groundwater risk and wastewater irrigation in Mexico

S. Health impact of wastewater use in Mexico. PublicHealth Rev 19:243-250 (1991).

3. Guti6rrez-Ruiz ME, Siebe C, Sommer I. Effects of landapplication of wastewater from Mexico City on soilfertility and heavy metal accumulation: a bibliograph-ical review. Environ Rev 3:318-330 (1995).

4. BGS. Impact of Wastewater Reuse on Groundwaterin the Mezquital Valley, Hidalgo State, Mexico. PhaseReport. Mexico City, Mexico:British Geological

Survey/CNA, 1995.5. INSP/Escuela de Salud Publica de M6xico.

Diagn6stico de Salud de la Jurisdicci6n Sanitaria No.3, Tula, Hidalgo. Cuernavaca, Mexico:lnstitutoNacional de Salud Publica, 1994.

6. INEGI. Mortalidad, Estado de Hidalgo. INEGI, vol. III,No. 2. Mexico City, Mexico:lnstituto Nacional deEstadistica, Geografia e Informatica, 1995.

7. Downs TJ. Water supply and wastewatertreatment/reuse. In: Environmental Quality,Innovative Technologies and Sustainable EconomicDevelopment: A NAFTA Perspective (Macari EJ,Saunders FM, eds). NewYork:ASCE, 1997;129-132.

8. Levine B, Madireddi K, Ye QF, Khan E, Stenstrom MK,Suffet IH. Treatment of trace organic compounds byozone/BAC for wastewater reuse: the LakeArrowhead Pilot Plant In: Beneficial Reuse of Waterand Biosolids Conference Proceedings, Marbella,Malaga, Spain, 6-9 April 1997. Alexandria, VA.WaterEnvironment Federation, 1997;8131-8/44.

9. U.S. EPA. Methods for Determination of OrganicCompounds in Drinking Water. EnvironmentalMonitoring Systems Laboratory. EPA-600/4-88/039.Washington, DC:U.S. Environmental ProtectionAgency, 1998.

10. U.S. Environmental Protection Agency. Method 625:base/neutral and acid (wastewater). 40 CFR Part 136,43385. Fed Reg 49(209):43385-43406 (1984).

11. Madden JM, McCardell BA. Vibrio cholerae. In:Foodborne Bacterial Pathogens (Doyle MP, ed). NewYork:Marcel Dekker, Inc., 1989;525-542.

12. WHO. Guidelines for Drinking-Water Quality, Vol. 2,Health Criteria and Other Supporting Information. 2nded. Geneva:World Health Organization, 1996.

13. Bitton G. Wastewater Microbiology. New York:Wiley-Liss, 1994.

14. McKone TE, Daniels Jl. Estimating human exposurethrough multiple pathways from air, water and soil.Regul Toxicol Pharmacol 13:36-61 (1991).

15. Intemational Commission on Radiological Protection.Report of the Task Group on Reference Man. ICRPNo. 23. New York:Pergamon Press, 1975.

16. CNA. Estudio de Calidad y Suministro de Agua paraConsumo Dom6stico del Valle de Mezquital. M6xicoDF:Comisi6n Nacional del Agua, 1995.

17. Edberg SC, Allen MJ, Smith DB, Kriz NJ. Enumerationof total coliforms and Escherichia coli from sourcewater by the defined substrate technology. AppIEnviron Microbiol 56:366-369 (1990).

18. APHA/AWWA/WEF. Standard Methods for theExamination of Water and Wastewater, edition 19(Eaton D, Celsceri F, Greenburg AE, eds). Washington,DC:American Public Health Association, 1995.

19. U.S. EPA. Method 608: organochlorine pesticideand PCBs. 40 CFR Part 136, 43321. Fed Reg49(209):43321-43336 (1984).

20. Glaser ER, Silver B, Suffet IH. Computer plots for thecomparison of chromatographic profiles. JChromatog Sci 15(221):22-28 (1977).

21. Suffet IH, Glaser ER. A rapid gas chromatographic pro-file/computer data handling system for qualitativescreening of organic compounds in waters at the part-per-billion level. J Chromatog Sci 16(12):12-16 (1978).

22. NBS. EPANNIH Mass Spectral Data Base. NBS Publ 63.Gaithersburg, MD:National Bureau of Standards, 1978.

23. Secretaria de Salud. Norma Oficial Mexicana NOM-127-SSA-1996. Limites permisibles de calidad ytratamiento para potabilizaci6n - salud ambiental,agua para uso y consumo humano. Mexico City,Mexico:Diario Oficial de la Federaci6n, 1996.

24. WHO. Guidelines for Use of Wastewater inAgriculture and Aquaculture. Tech Rpt Ser 778.Geneva:World Health Organization, 1989.

25. Juanico M. The performance of batch stabilizationreservoirs for wastewater treatment, storage andreuse in Israel. Wat Sci Technol 33(10-11):149-159(1996).

26. Fan AM, Steinberg VE. Health implications of nitrate andnitrite in drinking water an update on methemoglobine-mia occurrence and reproductive and developmentaltoxicity. Regul Toxicol Pharmacol 2335-43 (1996).

27. U.S. EPA. Integrated Risk Information Service (IRIS)Database. Washington, DC:Environmental ProtectionAgency, 1995.

28. Pontius FW. An update of the federal drinking waterregs. J Am Wat Works Assoc, February:48-58 (1995).

29. U.S. Environmental Protection Agency. The SafeDrinking Water Act: final regulations. Fed Reg44(34):part V (1994).

30. ATSDR/U.S. EPA. Top 20 Hazardous Substances.ATSDR/EPA Priority List for 1997. Available:http://www.atsdr.cdc.gov/cxcx3.html [cited 14 May199].

31. International Programme on Chemical Safety.Chlordane. Environmental Health Criteria 34.Geneva:World Health Organization, 1984.

32. Bevenue A, Hylin JW, Kawano Y, Kelley TW.Organochlorine pesticide residues in water, sedi-ment, algae and fish, Hawaii, 1970-71. J PesticMonitoring 6:56-64(1972).

33. International Programme on Chemical Safety.Polychlorinated Biphenyls and Terphenyls. 2nd ed.Environmental Health Criteria 140. Geneva:WorldHealth Organization, 1993.

34. Agency for Toxic Substances and Disease Research.Polychlorinated biphenyl (PCB) toxicity. J Toxicol ClinToxicol 28:505-526 (1990).

35. WHO/EURO. PCBs, PCDDs and PCDFs in Breast Milk:Assessment of Health Risks. Environmental HealthSeries 34. Copenhagen:World Health OrganizationRegional Office for Europe, 1988.

36. Downs TJ. Water Resources Management,Sustainability, Risk Assessment and Pollution byWastewater in the Mexico City Region [DrEnvDissertation]. Los Angeles, CA:University ofCalifornia, Los Angeles, 1998.

37. Silverstein J. Demonstration of BiologicalDenitrification of Drinking Water for RuralCommunities. Final Report-Phase 1. EPRI CR-108884.Leesburg, VA:Electric Power Research Institute, 1997.

38. Noyola A, Morgan JM. Proceso Anaerobio-An6xico-Aerobio (AAA) para la Eliminaci6n de MateriaOrganica y Nitr6geno de Aguas Residuales. MexicoDF:Coordinaci6n de bioprocesos ambientales,Instituto de Ingenieria, Universidad NacionalAut6noma de Mexico, 1998.

-- yes.Environmental me7ntsam Technical and Toxicology Re

* Chemical Health and Safety Database * Historical Control Datubase

Visit us online!-http://ehis.niehs.nih.gov

4 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.

hr~ttj

Environmental Health Perspectives * Volume 107, Number 7, July 1999 561