Degradation of the herbicide flamprop-isopropyl in soil under laboratory conditions

Yestic. Sci. 1979, 10, 1-13

Degradation of the Herbicide Flamprop-isopropyl in Soil under Laboratory Conditions Eric J. Hitchings and Terry R. Roberts

Shell Biosciences Laboratory, Sittingbourne Researrlr Centre, Sittingbourne, Kent ME9 8AG

(Maniiscript received I2 January 1978)

The degradation of the wild-oat herbicide flamprop-isopropyl, [isopropyl ( _+ )- N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate], in four soils has been examined under laboratory conditions with sampling times of up to 45 weeks after treatment. The major degradation product of [14C]flamprop-isopropyl in all soils at up to 10 weeks after treatment was the carboxylic acid (+)-N-benzoyl-N-(3-chloro-4- fluoropheny1)alanine. This compound in turn underwent degradation by loss of the benzoyl group and the propionic acid moiety, with evolution of [l*C]carbon dioxide to form 3-chloro-4-fluoroaniline (CFA). The CFA was formed slowly in soil and occurred mainly as a bound form. There was evidence to show that the CFA was subsequently converted into other polar products. The time for depletion of 50% of the applied herbicide was approximately 10 weeks in sandy loam and medium loam soils, 11 weeks in a clay loam soil and 23 weeks in a peat soil.

1. Introduction

The herbicide flamprop-isopropyl [isopropyl ( f )-N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate], Barnon,a has been developed for the selective control of wild oats (Avena spp.) in barley. It is applied post-emergence to barley and consequently it is necessary to consider its fate in soil as well as in plants.

CH, (1) (flamprop-isopropyl): R, - F; R, = -CH(CH,),

R, = F; R, = H (11) benzoylprop-ethyl . R, - Cl; R, = Et

R h ~ H - - c m R , co I

In plants, flamprop-isopropyl was shown to be metabolised by hydrolysis to the corresponding acid (11) and by oxidation in the benzoyl moiety to form mono-hydroxylated derivatives of flamprop- isopropyl itself and of 11.1 The structure of flamprop-isopropyl closely resembles that of the herbicide benzoylprop-ethyl of which the degradation in soil has been studied in some detaiL2 After hydrolysis of benzoylprop-ethyl to its parent acid, which underwent some binding with the soil, there followed a slow debenzoylation and decarboxylation leading to the formation of 3,4-dichloro- aniline (DCA). The DCA was formed slowly in the soil and did not occur in free form but was present mainly as a complex with the humic acid fraction.

For comparative purposes the degradation of flamprop-isopropyl has been examined using the same soils as those used in the earlier work with benzoylprop-ethyl. In addition, the effects on the degradation of flamprop-isopropyl of varying the moisture content of the soil and of varying the dosage rate of the herbicide have also been examined.

Barnon is a Shell registered trade name for flamprop-isopropyl.

0 0 3 1 - 6 1 3 X / 7 9 / 0 2 0 l $02.00 0 1979 Society of Chemical Industry

1 1

2 E. J. Hitchings and T. R. Roberts

2. Experimental

2.1. Radio-labelled compounds [14C]Flamprop-isopropyl was labelled separately in the halophenyl (3-cNoro-4-fluorophenyl) ring (specific activity 8.9 nCi pg-I), in the carbonyl of the benzoyl group (15.8 nCi pg-l) and in the carboxyl of the ester group (1 1.4 nCi pg-l). The radiochemical purity of each compound was determined by radio-gas-liquid chromatography (radio-g.1.c.) under the conditions described below, and the compounds were estimated to be > 99 % radiochemically pure.

2.2. Unlabelled reference compounds The unlabelled reference compounds are listed in Table 1 and their retention values (RF) in various thin-layer chromatographic (t.1.c.) systems are given in Table 2.

2.3. Soil treatments Four soils were used; these, with the exception of the medium loam which was obtained locally in Kent, came from various locations in East Anglia.2

Table 1. Unlabelled reference compounds

iv A B

Compound Structure

I (Flamprop-isopropyl) A: R1=-CH(Me)z; R2=R3=R4=H I1 A: R1= RS= R4= H

111 (Flamprop-methyl) A: R'=Me; R2=R3=R4=H IV A: Rl=-CH(Me)z; R2=OH; RS=R4=H V A: Rl=-CH(Me)z; R2=R4=H; R3=OH

VI A: Rl=<H(Me)z; R2=RS=H; R4=OH VI1 A: R'=H; Rz=OH; R 3 = H

VIII A: R l=H; RZ=R4=H; RS=OH 1 x A: R l=H; RZ=R3=H; R4=OH X A: Rl=Me; RZ=OMe; RS=R4=H XI B : R5 = -NH-CO-CaH5

XI1 (CFA) B: R5=-NHz XI11 B: R5=-NH-CH(Me)-COOH XIV B: R5=-NH-CH(Me)--COO-CH~Me)r

XVI xv B: R5 = -NH-CH(Me)-COOMe

B : R5 = -N=N-Ar XVII B: RS=-N(O)=N-Ar

Benzoic acid

CFA: 3-chloro-4-fluoroaniline.

Degradation of fiamprop-kopropyl 3

Table 2. Thin-layer chromatography of flamprop-isopropyl and reference compounds

RF value ( x 100) in System indicated ~

Compound

I (Flamprop-isopropyl) I1

111 (Flamprop-methyl) IV V

VI VII

VIII Ix X

XI XI1 (CFA)

XIII XIV xv

Benzoic acid XVI

XVII

1 2 3 4 5 6 7

56 33 68 43 < I 0 0 36 30

50 30 63 42 42 32 38 < 5 44 20 35 < 5 36 15

0 28 < 5 0 7 < 5 0 7 < 5

21 35 50 61 42 45 65 44

(10 0 37 70 75 53 60 50

50 95 90

86 50 0 78 83 90 65 88 75 88 38 0 45 0

0 21 82 90 76 85 10 53 0 80 90 90 90 95 67 95 A 40

CFA: 3-chloro-4-fluoroaniline. System: 1, acetone+petroleum spirit (3 +7 by volume).

2, dichloromethane. 3, chloroform + acetic acid (95 + 5 by volume). 4, toluene+acetic acid (9+ 1 by volume). 5, ethyl acetate+ acetic acid (49 + 1 by volume). 6, ethyl acetate. 7, petroleum spirit +dichloromethane (9+ 1 by volume).

Merck silica gel plates F254, 250 pm thick.

2.3.1, Laborutory soil jar experiments The aim of this work was to study the effect of varying the soil type, soil moisture content and application rate on the rate of degradation of flamprop-isopropyl in soil. [14C]Flamprop-isopropyl labelled in different positions was used as an aid to identification,

The treatments made are tabulated in Table 3. Samples of the soil (100 g wet weight) were mixed in glass jars with [14C]flamprop-isopropyl in acetone solution. The solutions were added dropwise to the soil, the soil being mixed during and after application by rotating the jars. The maximum volume of solvent added was 2 ml for each 100 g soil sample. After treatment the jars were closed with pierced lids (a single hole of 3 mm diameter) which enabled any volatile products formed to escape. The jars were stored in the dark at room temperature (15-20°C) until required. Loss of water was determined by weighing, and the moisture content of each soil jar periodically readjusted to its original value by the addition of distilled water.

2.3.2. Treatment under balance conditions In order to study the nature and quantity of any volatile products formed, a balance study experiment was set up. Samples of sandy loam (1OOg) were treated separately with [l4C]flamprop- isopropyl labelled in the carbonyl of the benzoyl group (2.5 mg) and [14C]flamprop-isopropyl labelled in the carboxyl of the ester group (1.9 mg). The soil was contained in a round-bottom flask connected to a series of traps containing (a) silica gel powder, (b) acetone at - 10°C and (c) 5 % aqueous sodium hydroxide solution. Air was drawn continuously through the system and the silica gel and sodium hydroxide solution traps were changed and radio-counted at intervals over a period


Table 3. Treatments of soil with [“T)flamprop-isopropyl

Soil type

Moisture content [14C]label

(% by weight) position

Medium loam Clay loam Peat Sandy loam Sandy loam Sandy loam Sandy loam Sandy loam Sandy loam

24.5 16 12 14 3 . 6

26.3 14.0 14 .0 14.0

Halophenyl ring Halophenyl ring Halophenyl ring Halophenyl ring Halophenyl ring Halophenyl ring Benzoyl Ester Halophenyl ring

Specific activity

(nCi pg-l)

8 . 9 8 . 9 8 .9 8 . 9 8 . 9 8 . 9

15.8 11.4 8 . 9

Treatment level (mg)

1.44 1.44 1.44 1.44 1.44 1.44 1.67 1.93 1.44a

Plus unlabelled flamprop-isopropyl (27.5 mg).

of 22 weeks after treatment. The system was maintained at 15-20°C under normal laboratory lighting.

The presence of [Wlcarbon dioxide was confirmed by initial radio-counting on the alkaline trap solution followed by the addition of barium chloride solution. The barium carbonate precipitate was removed by centrifuging and the supernatant liquid again radio-counted. No radioactivity was detected for this liquid.

2.4. Sampling and extraction Soils from the soil jar experiments were examined at the intervals indicated in the tables of results. They were extracted initially by end-over-end tumbling for 2 h with acetonitrile + water (7 + 3, by volume) using 2 ml of solvent for each gram of soil. The mixtures were filtered through sintered- glass discs and the soil residues were rinsed with acetonitrile (2 x 50 ml). The extracts were concentrated to an aqueous residue by evaporation under reduced pressure and then extracted twice with equal volumes of ethyl acetate. The ethyl acetate solutions were combined, concentrated and examined by t.1.c.

The soil residues were re-extracted by one of several different systems which were used throughout the course of the experiment: (a) cold distilled water for 2 h; (b) cold acetone + water (1 + 1 by volume) for 2 h and then hot distilled water (80°C) for 7 h; (c) hot acetone+water (1 + 1 by volume at 80°C) for 2.5 h. Cold extracts were carried out by tumbling as described previously. Hot extractions were carried out on an oil-bath under a water-cooled condenser with occasional swirling of the contents of the flask. This was further followed by extraction with 5 % aqueous sodium hydroxide solution at 80°C for 2 h and either 10% aqueous sodium hydroxide solution or 6~ hydrochloric acid for 1 h at 100°C. The extraction scheme used is summarised in Figure 1.

2.5. The leaching behaviour of soil degradation products In addition to the above samples a further two jars containing sandy loam soil (100 g) of moisture content 3.6% by weight and treated with 1.44 mg of halophenyl ring-labelled [14C]flamprop-isopropyl were taken at 45 weeks after application and mixed together. One half of the soil was extracted using the aqueous acetonitrile, hot aqueous acetone and 5 % sodium hydroxide solution system described above. The remaining half was packed into a glass column of 4.5 cm diameter, making a soil depth of 3.5 cm; water was allowed to pass through the column at a rate of 2 ml h-1 until some 1700 ml had been collected. The leachate was acidified (pH 2.0) with concentrated hydrochloric acid and then extracted twice with ethyl acetate. The extracted material was concentrated and examined by t.1.c.

Degradation of tiamprop-isopropyl 5

Soil treated with [ ''C]flamprop-isopropy1

1 extracted with

acetonitrile + water (7 + 3, by volume for 2 h)

1

extract partitioned with ethyl acetate

further extracted by (i) cold water (2 h) (ii) (a) cold aqueous acetone (1 + 1, by volume, 2 h)

(b) hot water (80°C for 7 h) (iii) hot aqueous acetone (1+ 1, by volume, 80°C for 2.5 h)

Soil residue treated with 5% aqueous sodium hydroxide) (80°C for 2 h)

cenirifuge * I ethyl a'cetate aqueous'solution

I freezedried

I t.1.c.

alkaline extract Soil residue

t.1.c. ' * partition partition

with diethyl with diethyl ether pH 1 L O ether pH 4.0

I centrifuge I

Residue containing more than 10% applied activity treated either with (i) 10% aqueous

sodium hydroxide (ii) 6M HCI (100°C for 1 h)

ether aqueous ether humic aqueous I solution t.1.c. acid solution

t.1.c. precipitate

- 7 alkaline extract 1 extract acid , partition with partition with diethyl ether diethyl ether

pH 11.0 pH 4.0 ether aqueous I solution I t .I.c.

centrifuge

1 aqueous I solution

t.1.c. ether humic aqueous t.1.c. acid solution

precipitate

Figure 1. Scheme for the extraction of soils treated with [14C]flamprop-isopropyl.

2.6. Examination of the extracts 2.6.1. Radio-counting The amount of radioactivity in the extracts was determined by liquid scintillation counting using an Intertechnique SL 40 instrument and a 2-(biphenyl4yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole : 2-[4-( 1,1,3,3-tetramethylbutyI)phenoxy](polyethoxy)ethanol: toluene (butyl-PBD : Triton X-100 :


toluene) scintillator solution. Any unextracted radioactivity in soil and plant samples was measured by combustion analysis in which any [Wlcarbon dioxide produced was absorbed in a basic scintillator solution containing phenethylamine.

2.6.2. Chromatography The radio-components present in the extracts were separated and examined on Merck silica gel F254

plates (0.25 mm thickness) using the elution systems shown in Table 2. The acids I1 and XI11 were not readily separated from each other, but their methyl esters could be resolved using System 5. The radioactive sites on the chromatogram were detected with a Desaga radioscanner or by auto- radiography using Kodak Kodirex X-ray film, DX-80 developer and FX-40 fixer. In general, 7 and 14 day exposures were used. Quantification of the radioactive sites was carried out by triangulation of the peak areas obtained on the scanner traces.

The presence of I and I11 (from the methylation of 11) in the extracts was confirmed by radio-g.1.c. using a Panax radioactivity detector linked to a Perkin-Elmer 452 gas chromatograph. The conditions used were as follows: column, 85 cni x 3 mm i.d., glass; column packing, 2% w/w OV-225 on 100/120 mesh Gas Chrom Q; oven temperature, 190°C; carrier gas, argon+ 5 % carbon dioxide at a flow rate of 70 ml min-'. Under these conditions the retention time for I was 4.58 min and for I11 was 4.63 min.

2.6.3. Chemical reactions The identity of some components was confirmed by further t.1.c. after one of the following chemical treatments.

( i ) Methylation The component to be methylated was isolated from the silica gel powder with methanol and was concentrated to less than 0.5 ml after which 3 ml of 5 % HCI in methanol was added. The mixture was held at 70°C for 1 h; after cooling, 5 nil of water was added. The solution was then shaken with diethyl ether and the ether solution was examined by t.1.c.

(ii) Acid hydrolysis The component to be hydrolysed was eluted from the silica gel powder with water and heated with 6M hydrochloric acid at 100°C for 1 h; the reaction mixture was cooled and extracted with diethyl ether, and the extract was examined by t.1.c.

(iii) Alkaline hydrolysis The component to be hydrolysed was eluted from the silica gel powder with water and heated with S-lO% aqueous sodium hydroxide at 80°C for 2.5 h or 100°C for 1 h. The reaction mixture was cooled, centrifuged and then extracted with diethyl ether before and after acidification with hydrochloric acid. The separate extracts were examined by t.1.c.

(iv) Acetylation The sample to be acetylated was treated with an excess of acetic anhydride in the presence of sodium acetate and the reaction mixture was heated to 80°C for 1 h. After cooling, the mixture was poured into water and the aqueous solution was extracted with chloroform. The chloroform layer was concentrated and examined by t.1.c.

(v) Hydrolysis of humic acid precipitates Some of the humic acid precipitates (see section 2.4) were subjected to acid and alkaline hydrolysis as described in sections (ii) and (iii) above. The resulting mixtures were centrifuged and the aqueous solutions were extracted with diethyl ether. The ether solutions were examined by t.1.c.

Degradation of Hamprop-isopropyl 7

3. Results and discussion 3.1. Identification of the soil degradation products Using the t.1.c. systems listed in Table 2 it was shown that there were at least seven degradation products present in the soil extracts (see Tables 4-7). Typical radioscans of chromatograms are shown in Figure 2. The presence of 11, XI and XI1 was confirmed by co-chromatography with authentic standards in several elution systems. The two acids I1 and XI11 were separated by con- version into their methyl esters and eluting on t.1.c. using System 2. The identities of the two acids were conlirmed by co-chromatography of the separated methyl esters with authentic standards in several elution systems. The identity of XI1 was confirmed by acetylation and comparison of the resulting product on t.1.c. with an authentic acetylated standard. A number of hydroxylated derivatives were available for comparison purposes (see Table 1) but these were not detected as degradation products of flamprop-isopropyl in soil.

Two polar fractions were shown to be present in many of the soil extracts. Polar fraction A was polar material that partitioned from water into organic solvents such as ethyl acetate or diethyl ether. When subjected to acid and alkaline hydrolysis polar fraction A was shown to give the acid I1 and, in the case of acid hydrolysis, flamprop-isopropyl was also produced. Polar fraction B was polar material that did not partition into organic solvents but remained in aqueous solution.

One aqueous acetone extract of the sandy loam soil samples at 45 weeks after treatment with halophenyl ring-labelled [14C]flamprop-isopropyl was shown on t.1.c. to contain a minor non-polar component. This component, which constituted 0.2% of the applied radioactivity, had an RF value of 0.95 in both elution Systems 2 and 4. In these two systems this RF value corresponded to that for XVI (3,3'-dichloro-4,4'-difluoroazobenzene) and XVIII (3,3'-dichloro-4,4'-difluoroazoxybenzene). However, further examination in other t.1.c. systems showed that this component was not XVI or XVII. Insufficient material was available for the characterisation of this minor component.

The humic acid precipitates obtained after treatment with 5 % sodium hydroxide retained some radioactivity and were hydrolysed with acid and alkali, the resulting products being examined by t.1.c. Most of the radioactivity associated with the precipitate was not released by hydrolysis. Such radio-labelled material as was released appeared to be polar in nature and had properties similar to those of polar fraction B. Small amounts of radio-label were, however, shown to be I1 and XII.

3.2. Evolution of [ 14C]carbon dioxide from soil treated with [14C]flamprop-isopropyl Further evidence of the ultimate formation of products derived from 3-chloro-4-fluoroaniline in soil was provided by the balance studies which showed that [14C]carbon dioxide was released from both the carbonyl of the benzoyl group and from the ester group of the propionic acid moiety. The amount of [Wlcarbon dioxide produced was 9.0% from the soil treated with benzoyl-labelled [14C]flamprop-isopropyl and 12.5 %from the soil treated with ester-labelled [14C]flamprop-isopropyl. The small amounts of material trapped by the silica gel columns were found to be the parent compound I (see Table 8). The acetone trap was discontinued after 3 weeks when it was evident that no radioactivity was being collected by it. At the end of the experiment the soil was extracted with aqueous acetonitrile and the extract was found to contain mainly I and I1 in line with the soil jar experiments. The low recovery of the radio-label from soil treated with benzoyl-labelled [14C]- flamprop-isopropyl could have been due to inefficient trapping of volatile components.

3.3. The leaching behaviour of flamprop-isopropyl and its degradation products Although the precise nature of the polar products formed from flamprop-isopropyl in soil is not known, a leaching experiment (see Table 9) showed that these products were leached from soil by water to only a very limited extent even when 1.7 litre of water (equivalent to 1020 mm of rainfall) has passed through the soil over a 70-day period. In addition to polar material the leached water was also shown to contain some of the acid I1 and small amounts of XII.

3.4. The concentration of flamprop-isopropyl and its degradation products in soil There were no apparent differences in the nature of the degradation products formed when [14C]-

Tab

le 4

. T

he d

egra

datio

n of

['4

C]f

lam

prop

-isop

ropy

l in

a s

andy

loam

soi

l (re

sults

exp

ress

ed a

s pe

rcen

tage

of

appl

ied

radi

oact

ivity

)

Hal

ophe

nyl

ring

labe

l B

enzo

yl la

bel

Est

er la

bel

Hal

ophe

nyl r

ing

labe

l (1.

44 m

g)

(28.

94m

g)

(1.6

7mg)

(1

.93

mg)

3.6

% M

oist

ure

14%

Moi

stur

e 26

% M

oist

ure

14%

Moi

stur

e 14

% M

oist

ure

14%

Moi

stur

e

Samplingtimeafterapplication(weeks)

3 10

28

3

4 10

28

3

10

28

4 10

4

10

28

4 10

28

Ext

ract

ed b

y so

lven

t sys

tem

":

I (F

lam

prop

-iso

prop

yl)

n XI11

XI

Pola

r A

Pola

r B

Subs

eque

ntly

extr

acte

d w

ith 5

%

sodi

um h

ydro

xide

at 8

0°C

for 2

h

Xu (

CFA

)

(a)

(c)

(c)

(a)

(a)

(b)

(c)

92

92.7

86

.7

89.0

75

.2

47.7

18

.1

0 0

.1

1.8

8.3

15

.5

16.9

8.

7 0

0 0

0 0

10

.1

0

00

00

:}<,

.I

b.

3

00

0-

0

0 1.

6 0

0.2

0.5

0.3

0.4

0 3.

1

0.3

- -

13.0

34

.1

__

(a)

(c)

(c)

(a)

(c)

85.0

54

.2

25.1

96

.5

83.6

7.

0 27

.2

7.4

2.8

7.7

00

00

0

00

00

0

00

00

0

0 0

1.25

0

0 0

.1

0.8

1.30

0

.3

1.3

(a)

82.5

16

.1

0 0 1 .O

b b

(b)

(c)

(a)

55.7

22

.5

81.6

21

.1

9.6

13

.8

bb

O

<0.

1 0.

18 -

bb

-

0 0.

17

0 0

0.79

0

.4

(b)

67.7

18

.2

0 -

-

0 0

(C)

38.0

11

.9

0 b b 0 2.63

_-

29.8

- - -

2.4

9.8

-

2.4

10.2

Une

xtra

cted

rad

ioac

tivity

1.

0 0.

2 0.

2 2.

0 7.

0 7.

8 9.

7 3.

5 7.

7 6.

8 1.

4 2.

0 5

.9

2.0

1.

2 4.

1 1.

9 1.

7

Tot

al

93.0

93

.2

89.5

99

.6

98.1

85

.4

75.6

95

.6

89.9

71

.7 1

01.0

94

.6 1

05.5

81

.2

44.2

99

.9

90.2

64

.4

a So

lven

t sys

tem

s use

d: (

a), a

ceto

nitr

ile+w

ater

(7+

3 by

vol

ume)

follo

wed

by

cold

wat

er fo

r 2 h

; (b)

, ace

toni

trile

+wat

er (

7+3

by v

olum

e) fo

llow

ed b

y co

ld a

queo

us a

ceto

ne

(1 +

1 by

vol

ume)

for

2 h

, an

d ho

t w

ater

for 7

h; (

c),

acet

onitr

ile+w

ater

(7+

3 by

vol

ume)

follo

wed

by

hot a

queo

us a

ceto

ne (1

+ 1

by v

olum

e) f

or 2

.5 h

. T

his

com

poun

d w

ould

not

be

dete

cted

with

the

rad

io-l

abel

in t

his

posi

tion.

Degradation of flamprop-isopropyl 9

flamprop-isopropyl was applied to four different soils. The carboxylic acid I1 was a major metabolite and its concentration reached a maximum at 4-10 weeks after treatment in all soils except peat. Other metabolites extracted by neutral solvents were XI, XI1 and XIII together with highly polar materials. Unchanged flamprop-isopropyl was also found in all soil extracts examined.

As the storage time of soils treated with [14C]flampropisopropyl increased a larger proportion

Table 5. Re-extraction of sandy loam soil residues (see Table 4) with 5% aqueous sodium hydroxide (results expressed as percentage applied radio-

activity)

Halophenyl ring Benzoyl Ester label label label

(1.44 mg) (1.67 mg) (1.93 mg)

Moisturecontent 14% 26.3% 14% 14 % ~~

Sampling time after application(weeks) 10 28 28 10 28 10 28

4.9 2 .4 0.35 0.27 0.7 0.67 }1J 0 0 II a 0 0

I1 XIII XI 0 0 0 0.3 0.14 a 0

XI1 2.2 2.2 1.7 a a a n

Polar A 1.7 5.1 1.0 0 .3 0.4 0 0.9 Polar B 4.0 11.2 9 .6 1.0 6.1 1.4 5.8 Radioactivity in humic acid

precipitate 4 .0 10.7 15.1 0.4 2.9 0 .3 2.7 Final unextracted radio-

activity 7.8 9.7 6.8 2 .0 1.2 1.9 1.7

aThis compound would not be detected with the radio-label in this position.

Table 6. The degradation of [14C]flamprop-isopropyl in four soils treated with 1.44 mg halophenyl-labelled [14C]flamprop-isopropyl (results expressed as percentage of applied radioactivity)

Soil type Medium loam Clay Peat Sandy loam

Moisture content 24.5 % 16.0% 72.0% 14.0%

Sampling time after application(weeks) 4 10 28 4 10 28 4 10 28 4 10 28

~

( I ) Extracted by solvent system indicated" (a) (c) (c) (a) (c) (c) (a) (c) (c) (a) (b) (c)

I (Flamprop-isopropyl) 80.7 49.4 12.5 85.0 51.1 29.3 97.0 75.5 43.0 75.2 47.7 18.1 I1 14.4 13.3 6.9 10.9 27.6 12.7 2.4 9.8 11.7 15.5 16.9 8.7

XI11 XI

XI1 Polar A Polar B

0 0 0 0 0 0 0 0 < 0 . 1 0

0 0 0 1.1 0 0 0 .7 0 0 0.9 0 0 1.6 0 .3 0 2.1 0 0 3.8 0 0 3.9 0.4 0 3.1

j::: :.25 h . 2 5 0.23

Subsequently extracted with 5 % aqueous sodium hydroxide at 80°C for 2 h - 20.6 45.9 - 8.2 30.8 - 6.6 14.9 - 13.0 34.1

Unextracted radioactivity 6.3 8.8 12.8 1 .4 3.4 10.7 3.4 4.9 19.0 7.0 7.8 9.7

Total 101.7 92.5 81.6 97.3 90.6 88.7 102.8 96.8 93.5 98.1 85.4 75.5

For composition of solvent systems (a), (b) and (c), see footnote to Table 4.


Table 7. Re-extraction of soil residue (see Table 6) with 5 % aqueous sodium hydroxide at 80°C for 2 h (results expressed as percentage applied radioactivity)

Medium Soil type loam Clay Peat Sandy loam

~~

Sampling time after application(weeks) 10 28 10 28 10 28 10 28

~ ~~

I1 0 . 7 2 . 9 0 . 7 0 .8 1 . 8 1 .5 4 , 9

XI 1 . 0 0 0 0 0 0 0 0 XI1 1 .4 2 .1 0 . 9 3 .0 0 0 . 9 2 .2 2 . 2

Polar A 5.0 5 . 8 1 . 1 5 . 7 0 . 8 1.0 1.7 5 . 1 Polar B 6 . 9 7 . 8 2 . 8 8 . 3 0 . 9 2 .2 4 . 0 11.2 Radioactivity in humic acid

precipitate 5 . 6 27.3 2 . 7 13 .0 3 . 1 9 . 3 4 . 0 10.7

Finalunextractedradioactivity 8 . 8 12.8 3 . 4 10.7 4 . 9 19.0 7.8 9 . 7

XI11 0 0 0 0 0 0

of the applied radio-label could not be extracted by the organic solvents used and it was necessary to treat those soil samples which retained bound radio-labelled material with 5 % sodium hydroxide at 80°C and 10% sodium hydroxide at 100°C for 1 h. These extractants released I1 and XI1 from the soil; both these compounds had presumably been present in the soils as bound forms. Further quantities of polar fractions A and B were also extracted.

A sample of polar fraction B isolated from soils at 28 weeks after treatment was hydrolysed by acid and alkali giving I1 as the major product. It would appear, therefore, that polar fraction B contained a bound or complexed form of I1 which was extracted intact by aqueous acetonitrile. However, as the amounts of polar materials A and B formed from halophenyl ring-labelled I was siderably greater than from benzoyl- or ester-labelled I, it is apparent that the polar products also contained residues derived from the halophenyl ring (XII).

6 I - v)

v)

c 3 0

c

2 4 c C

0

U 0

; 2

0

0

-- 6 'In

a 5 4 8

s

v)

c

U

&

- - 0 TI

2

0 60 40 2 0 0

Retention volue (R,) x 100 Retention value (R,) Y 100

Figure 2. Typical radioscans of thin-layer chromatograms of soil extracts. Sandy loam soil was treated with halophenyl label [14C]flamprop-isopropyl. The soil was extracted, 28 weeks after treatment, successively with acetonitrile+ water (7+ 3 by volume) aqueous acetone ( 1 + I by volume) at 80°C for 2 h. T.1.c. was performed on silica gel F254 plales. (a) Aqueous acetonitrile extract eluted with 5 % acetic acid in chloroform; (b) aqueous acetone extract eluted with 10% acetic acid in toluene. X, Peak scanned at one-third original sensitivity.


Table 8. The degradation of [14C]flamprop-isopropyl in soil under balance conditions. Volatile products were collected over a period of 22 weeks after treatment (results expressed as percentage of

amount applied)

Benzoyl Ester label label

Amount applied (mg) 2.5 1 . 9

[14C]Carbon dioxide 9 .0 12.5

Acetonitrile+ water (7 + 3, by volume) Radio-label in silica gel trap 0 . 0 3 0.5

Unextracted radioactivity 4 . 5 10 5 extract of soil after 22 weeks 58.7a 74.56

Total 7 2 . 2 98.0

Consisting of I (40 .9%) and I1 (17.8%). Consisting of I (62.9 %) and 11 ( I I . 6 %).

3.5. The rate of degradation of flamprop-isopropyl The rate of degradation of flamprop-isopropyl varied with the soil texture. The time required for 50% of it to disappear under the conditions used was approximately 10 weeks in sandy loam and medium loam soils, 11 weeks in a clay loam and 23 weeks in a peat soil. These rates of depletion were considerably slower than for benzoylprop-ethyl herbicide in the same soils.2 There appeared to be no correlation between the rate of degradation of flamprop-isopropyl and the organic matter content of the soil, as was observed with benzoylprop-ethyl.2 There was a marked effect on the degradation rate by varying the soil moisture content. In a dry sandy loam soil (3.6% by weight of moisture) 87 % of the applied flamprop-isopropyl remained in the soil at 28 weeks after treatment. In the same soil with a more commonly encountered moisture level (14%) only 18 % of the applied flamprop-isopropyl was present after 28 weeks. There was a slightly slower degradation rate in a wet soil (28%) moisture than in the soil with 14% moisture.

The concentration of I1 in soils increased to a maximum of 1 6 1 8 % of the applied radio-label in sandy loam, medium loam and peat and 28 % in clay loam. The concentrations of other (mainly

Table 9. The leaching of flamprop-isopropyl and its metabolites through soil

Concentration (expressed as % of applied activity)

Total analysis Radioactivity of soil prior leached through

Component to leaching soil

Flamprop-isopropyl Free IIa Bound I1 Free XIIa Bound XI1 Polar A Polar B Radioactivity in humic acid

Unextracted radioactivity

Total

precipitate

13.2 5 . 1

- 7.36

10.7 19.1

8 . 0 15.3

78 .7

I . 3 4 . 9

0.04 0 .07 0 .58 2 . 8 2

-

9.71

Extracted by acetonitrile+water (7+ 3, by volume). I, Associated with fine soil particles.

Bound

0

Figu

re 3

. T

he p

ropo

sed

degr

adat

ion

path

way

of f

lam

prop

-isop

ropy

l in

soi

l. 11

, N-benzoyl-N-(3-chloro-4-fluorophenyl)alanine;

XI,

N-(3-chloro-4-fluorophenyl)-

benz

amid

e;

XII

, 3-chloro-4-fluoroaniline (C

FA

); X

III,

N-(3-chloro-4-fluorophenyl)alanine.


polar) products increased during the 28 weeks after treatment at the end of which time these products accounted for between 36% in peat and 62% in medium loam.

4. Conclusions

The degradation of flamprop-isopropyl in soil proceeded by hydrolysis to the carboxylic acid I1 which then underwent degradation by debenzoylation and loss of the propionic acid moiety. This produced 3-chloro-4-fluoroaniline (CFA) which was present in the soil mainly in a bound form. Polar products were also formed and there is evidence to suggest that they were at least in part derived from CFA (see Figure 3). The rate of degradation of flamprop-isopropyl in soil was slower than that of benzoylprop-ethyl in the same soils.

Acknowledgements The authors thank their colleagues at Shell Biosciences Laboratory who have helped with this work, in particular Mr P. A. Harthoorn for radio-synthesis of the herbicide and Mr C. Jackson for technical assistance.

References 1. 2.

Roberts, T. R. Pestic. Biochem. PIiysiol. 1977, I, 378. Beynon, K. I . ; Roberts, T. R.; Wright, A. N. Pestic. Sci. 1974, 5, 451.

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Degradation of the herbicide flamprop-isopropyl in soil under laboratory conditions