Edwarh et al. : Movement of Chloflenrinphos in Soil 1

Movement of Chlorfenvinphos in Soil by M. J. Edwards, K. I. Beynon, C. A. Edwards and A. R. Thompson Shell Research Ltd., Woodstock Agricultural Research Centre, Sittingbourne, Kent, and Rothamsted Experimental Station, Harpenden, Herts. (Revised Manuscript received 26 August, 1970)

The leaching of chlorfenvinphos through soil was studied in twu field experiments by applying it to sloping arable land at 22 kg active ingredientlha and following its movement down the slope. Only very small quantities of the insecticide later appeared lower down the slope and at the bottom. In one of these experi- ments there was a pond at the bottom of the slope and residues could not be detected in the mud or water /rom this pond. Residues of the main soil metabolites of chlorfenvinphos could not be deterred in the pond water at 23 and 36 weeks after application.

Chlorfenvinphos was applied at the same dosage to the surface of the soil in the first compartment of a trough that sloped from the treated end with a gradient of I : 3.7 and consisted of six compartments containing soil to a height of 5 cm above the height of the transverse partiriotis. Leachates were collected at the bottom of each compartment. Most of the chlorfenvinphos in the leachates was collected during the first 9 weeks froin the first compartment. Only 0.18% of the amount of insecticide applied was leached through the soil but this was nine rimes more than was observed with dieldrin in a similar experiment. Only small amounts moved down the surface of the slope. More chlorfenvinphos leached vertical1.v into drainage water than laterally over the surface.

Introduction IT has been shown' that only small amounts of chlor- fenvinphos remained 38 weeks after it was applied at up to 9 kg a.i./ha on flat land and it has been foundz that the initial half-life of chlorfenvinphos in soils varied from 3 weeks to more than 23 weeks, depending on soil type, pesticide formulation and dosage level.

There is good evidences-6 that small amounts of chlori- nated hydrocarbon insecticides can move down the surface of sloping land, probably by transportation of treated soil particles by run-off water. It seems likely that a more soluble insecticide like chlorfenvinphos (solubility in water = 105 ppm at 22"c) would not only leach more than the insoluble chlorinated hydrocarbon insecticides into drainage water but would also move over the surface of sloping land more readily unless it were strongly ad- sorbed on to soil. Thus there could be a possibility of natural waters becoming contaminated. The present work reports measurements of the movement of chlorfenvinphos on the surface of sloping land and into ponds in two field experiments and studies of its movement down a sloping trough by a method already described ear1ier.O

Experimental Field experiments

The 6rst field experiment in 1967 studied the movement of chlorfenvinphos from .sloping arable land into nearby water. The site (Fig. l), which was uncontaminated by residues that could interfere with the detection of small concentrations of chlorfenvinphos, was the corner of a field that bordered a small pond at Bethersden, Kent. The soil was clay loam sown with spring barley during early March 1967. The pond measured -27 x 18 m and was -3 m deep in the middle with its surface -1 m below the bank. The cropped field bordered half its circumference and the rest was surrounded by trees and pasture.

Chlorfenvinphos (24 % emulsifiable concentrate) was mixed with water and applied on 14 March, 1967 at a rate of 22 kg a.i./ha to a strip (Sl, Fig. 1) 14 m long and 1.8 m wide, -8 m from the edge of the pond; the insecti- cide was not incorporated into the soil. Two strips, S, and Ss (Fig. I), the same size as the treated one &), were marked with stakes between S, and the edge of the pond, with a discard path 1 m wide between strips.

Soil cores were taken with an auger by leaning over the plot whilst standing on the surrounding, untreated soil. Fifteen cores, 2.5 cm dia. and 25 cm deep, were taken from

'\

a\-.- Fig. 1. Layouf of pond experiment at Bethersden, Ke1.t

each sector on each sampling date. The soil from each strip was bulked and taken back to the laboratory for analysis. Cores of 2.5 cm dia. and 25 cm deep were also taken from a strip of mud under water (Point T, Fig. 1) to a depth of about 10 cm.

Water samples of 3 to 5 litres were obtained by bulking 100-200 ml subsamples taken randomly from different parts of the pond. The samples of soil and mud, and those of water, were stored for up to 4 weeks at - 10"c and 0"c respectively, whilst awaiting analysis, previous studies having shown that the residues were stable under these conditions. A rain gauge was placed by the pond at the beginning of the experiment and rainfall measured regularly.

The samples of soil, mud and water were analysed for residues of chlorfenvinphos (fi-isomer) as described pre- viously.' Some samples of the soil and water were also analysed for residues of its major soil metabolites,* 1 -(2',4'-dichlorophenyl)-ethan-l-ol and 2',4'-dichloroaceto- phenone. The efficiency of the procedure was checked by adding known amounts of chlorfenvinphos to soil, mud and water samples before the extraction, and processing them as for the other samples.

In the second field experiment at Wix, Essex (Fig. 2)

Pestic. Sci., 1W1, Vol. 2, January-February

2 .

Edwards et al.: Movement of Chlorfenvinphos in Soil

The slopes of xy'and x'y'and xx' Y' were about 1:19

~

xx' and y were about 80 crn 5'6 cm and 10 cm higher than 'y/

Fig. 2. Layout of the experiment at Wix, Essex

there was no pond involved but the movement of chlor- fenvinphos down sloping land was studied in much the same way as at Bethersden. There was a treated strip 11 x 2 m at the top of the slope and three untreated strips of similar size were marked out lower down the slope (Fig. 2). Chlorfenvinphos (24 % emulsifiable concentrate) at a dose of 22 kg a.i./ha was applied after dilution with water on 9 April 1968. The field was later sown with barley. At intervals after treatment, 12 soil cores (2.5 cm dia., 25 cm deep) were taken from each strip and these were divided into upper (0-15 cm) and lower (15-25 cm) sections; all samples from the same strip and stratum were bulked. Residue analyses were carried out as described for the Bethersden experiment.

Trough experiments The movement of dieldrin down a sloping trough has

already been reported;E this trough (Fig. 3) was designed so that any insecticide that leached down the sloping surface of the soil would appear in the leachate from the various compartments. In this way the two main com- ponents of movement, horizontal run-off and vertical leaching, can be distinguished.

The trough was filled with silt loam soil on 16 February, 1968 and left to settle outdoors until 29 February. The soil surface was 5 cm above each partition, to give a slope from the treated end to the untreated end of 1 : 3-7. Chlorfen- vinphos (24 %emulsifiable concentrate dissolved in acetone) was sprayed on to the surface of the soil in the first and uppermost compartment at a dosage level of 22 kg a.i./ha. The surface of the soil in the other compartments was covered during spraying but the covers were later removed and the trough exposed outdoors to normal rainfall. Before the insecticide was applied, 5 soil samples (2.5 cm dia., 15 cm deep) were taken from each compartment and 3 more (2.5 cm dia., 7.5 cm deep) were taken immediately after applying the insecticide. Analyses of these latter samples for residues showed that the initial concentration of chlorfenvinphos in the treated compartment was 37 ppm (relative to the weight of dry soil). Additional soil samples were taken at 10 and 20 weeks from treatment. Soil was added to the hole left by the auger and this spot was avoided in subsequent sampling. The amount of rain was recorded by a rain gauge.

The leachates from the compartments were collected through rubber tubing into Winchester bottles and these were removed and replaced by empty ones at 9, 10 and 17 weeks after treatment. The leachates were stored at

Jnvn glass plate sidqends and partitions 6 rnrn glass plate bottom 38 mrn dia.funnels

Fig. 3. Trough used to h l d soils for outdoor leaching experiments

5"c for a few days and 250ml subsamples were taken from which the insecticide was extracted with re-distilled light petroleum ether. The residues were determined by gas-liquid chromatography as described previously.

The amount of insecticide collected in each bottle was usually related to the amount of water that was collected. The results may be considered as the total weight of insecticide collected from each compartment or as the concentration or weight leached by a unit volume of water.

Results Field experiments

Table I shows the quantities of rain that fell during the course of the experiments and Table 11 summarises the relative soil particle sizes for the two sites. The residues in soil, mud and water at Bethersden are summarised in Table I11 and those for soil at Wix are given in Table IV.

Trough experiments Tables V and VI summarise the concentrations and

weights of chlorfenvinphos in the leachates. The amounts of rain falling were 9.0 cm in the first 9 weeks, 3.1 cm from the 9th and 10th weeks and 7.7 cm between the 10th and 17th week. The amounts of leachates collected are given in Table V.

Discussion Field experiments

The amount of chlorfenvinphos applied in both experi- ments was about 5 times the usual agricultural dosage. The land also sloped quite steeply, so conditions greatly favoured transport of insecticide residues down the slope. In the trial at Bethersden, the initial half-life of the residues in the treated strip was a little over 4 weeks. After 8 and 23 weeks there was no significant penetration of chlor- fenvinphos to the soil below 15 cm depth. In the strips Sa and SB, residues of 0.05 and 0.03 ppm respectively, of the /?-isomer were detected 4 weeks after application but these had disappeared by the 8th week after treatment and did not re-appear. Hence, although some of the insec- ticide moved over the surface of the soil, the amounts were small and transient and no detectable amounts reached the pond mud or the pond water at Bethersden within 36 weeks of application. It has been showna that chlorfenvinphos

Pestic. Sci., 1971, Vol. 2, January-February

Edwards et al. : Movement oj' Chlorfenvinphos in Soil 3

TABLE I Amounts of rain in field experiments

Bethersden Wix

Time after Amount of Time after Amount of treatment, rain, cm treatment, ram, cm

0-4 4.6 0-2 2.5 4-8 3.8 2-4 7.6 8-17 5.1 4-14 12.7 Total 13.5 Total 22.8

weeks weeks

TABLE I1 Particle analysis of soils, % by wt,

Particles Bethersden Wix site site

____~ ~~

Sand 19 32 Silt 45 27 Clay 32 37

persists for only a few days in water but appreciable amounts can remain in mud for several weeks if the amount of insecticide in the water is large. In the present work the pond was well stocked with fish and at no time during the trial were dead or moribund fish observed.

The conclusions reached in the Bethersden experiment were confirmed in the experiment at Wix. The insecticide persisted in the treated strip rather longer than at Bethers- den, and whilst appreciable amounts of chlorfenvinphos appeared at soil depths below 15 cm, suggesting that some had leached down from the surface soil, it is impossible to be certain that some contamination of the lower soil did not occur during sampling.

It seems clear that surface run-off or leaching of chlor- fenvinphos and its major soil metabolites into drainage water from treated agricultural land is unlikely to be a serious problem.

Trough experiments Most of the leaching of chlorfenvinphos occurred during

the first 9 weeks after treatment. The insecticide was mainly in the water from the first compartment and resulted from leaching vertically downwards. Thereafter, although more

TABLE 111 Analysis of soil, mud and water samples after chlorfenvinphos* was applied to a slope near a pond, ppm

Site of trial: Bethersden, Kent Chlorfenvinphos applied at 22 kg a.i./ha

Sampling Days after treatment

(Fig. 1) Pre-treatment 1 28 56 161 Sample position

<0.01 8.7 4-7 2.6 0.09 <0.01 0.05 t0.01 to01

<0.01 <0.01 0.03 <0.01 <0.01 <0.01

Soil? s, S , < 0.0 1 ss

Mud T <0.01 <0.01 <0.01 t0.01 Water - <0.0005 <0*0005 <04005 <0.0005 <04005

* Relative to the dry weight of soil or mud t Sampled to 15 cm depth Mean recovery of chlorfenvinphos was:

101 % at the 0.1-20 ppm level from soil 92% at the 0.024.05 ppm level from mud

100 % at the 0.054.01 ppm level from water Residues of 1-(2',4'-dichlorophenyl)-ethan-l-ol (0.6 ppm) and of 2',4'-dichloroacetophenone (0.08, 0.10 ppm) were detected in the soil in S1 at 4 and 8 weeks after application but the residues were below 0.01 ppm at 23 weeks after application and were below 0.001 ppm in the pond water at 23 weeks and 36 weeks from application

TABLE IV Analysis of soil samples for residues* of chlorfenvinphos, ppm

Site of trial: Wix, Essex Chlorfenvinphos applied at 22 kg a.i./ha

Sampling Depth of position sample, (Fig. 2) cm

A 0-1 5 15-25

D 0-1 5 15-25

Weeks after treatment

Pre-treatment 0 2 6 10 14

< 0.02 < 0.02 < 0.02 <0.02 t0.02 < 0.02 < 0.02 <0.02

5.9 n.d. n.d. n.d. n.d. n.d. a d . n.d.

5.1 0.65 t 0.02

< 0.02 < 0.02 < 0.02 < 0.02 <0.02

6.3 0.03

< 0.02 <0.02 <0.02 <0.02 <0.02 < 0.02

4.2 1.1 t

< 0.02 < 0.02 < 0.02 < 0.02 <0.02 <0.02

3.7 0.06

< 0.02 < 0.02 < 0.02 < 0.02 < 0.02 < 0.02

* Relative to the dry weight of soil t Results are high compared with those obtained 4 weeks later and may indicate contamination from the 0-15 cm layer during sampling Mean recovery of chlorfenvinphos from untreated soil was 95 % at 0.10-10 ppm level

Pestic. Sci., 1971, Vol. 2, January-February

4 Edwards et al. : Movement of Chlorfenvinphos in Soil

TABLE V Concentrations of chlorfenvinphos in leachates from the trough

Vol. of water leached Compartment Residue (ppm) in leachate through compartment, ml

No. 0-9 weeks 9-10 weeks 10-17 weeks 0-9 weeks 9-10 weeks 10-17 weeks

1 0.18 0044 0.052 1350 500 200 2 0.007 <0.001 0.016 450 530 300 3 o m 2 <0401 0.002 2100 1270 800 4 < o m 1 <0~001 <0.001 900 600 200 5 <0~001 <0.001 < 0.00 1 1880 1350 780 6 0.01 I <0401 <0~001 2000 2850 2050

Total -0.2 -0.044 4 . 0 7 0 8680 7100 4330

Mean recovery of chlorfenvinphos when added to untreated water was 99% at the 0.01-5 ppm level

TABLE VI Weights of chlorfenvinphos in leachates from the trough

Compartment Residue, pg No.

0-9 weeks 9-10 weeks 10-17 weeks

10.4 * 4.8 1 243 22 2 3.2 -

1.6 3 4.2 4 5 6 22

- - - - - - -

- -

Total 272 22 17

* Below limit of detectability (= <0001 ppm)

rain fell than during the first 9 weeks, much less chlor- fenvinphos was leached. This was probably because during the initial period the insecticide was considerably more concentrated in the soil (see Table VII); also, it would become progressively more adsorbed on to soil and held there. Such gradual adsorption has been demonstrated by several workers.*

The analysis of residues in soil at the end of the experi- ment provided evidence that some of the insecticide ran down the surface of the slope; appreciable quantities were found in the surface soil as far along as compartment 4 (Fig. 3) but little in the lower levels of soil. It is interesting that although 22 pg of chlorfenvinphos were collected in the leachates from compartment 6 very little was detected in the soil from that compartment. It seems probable that the insecticide moved in water over the surface of the slope and down the end of the box to the outlet.

The amounts of chlorfenvinphos appearing in the leach- ates were about nine times greater than in a similar experiment using dieldrins (3 11 pg of chlorfenvinphos leached compared with 34 pg of dieldrin following the application of similar doses, the experiments being carried out at the same time).

Although some chlorfenvinphos was leached from the treated soil the amounts were small compared with the

TABLE VII Analysis of soil in the trough for residues of chlorfenvinphos

Soils samples taken immediately before treatment contained <0.01 ppm of chlorfenvinphos

A sample from compartment 1 taken to 7.5 cm depth immedi- ately after treatment contained 37 ppm of chlorfenvinphos

Residues* (ppm) at Compartment Depth of intervals after

10 weeks 20 weeks

No. s a m p 1 e , treatment cm

1 0-7.5

2 0-73

3 0-7.5

4 0-7.5

5 0-7.5

6 0-7.5

7'5-15.0

7.5-15.0

7.5-15.0

7.5-15.0

7.5-15.0

7.5-15.0

28.0 7.4 0.64 0.30 0.10

< 0.0 I 0.03

<0.01 <0.01 <0.01 <0.01 <0.01

6.3 0.77 0.3 1 0.02 0.05

< 0.01 <0.01 <0.01 < 0.0 1 <0,01 <0.01 <0.01

* Relative to dry weight of soil Mean recovery of chlorfenvinphos when added to untreated

soils prior to analysis was 102% at the 1 ppm level

dose initially applied to compartment 1. The addition consisted of 173 mg of chlorfenvinphos and the total amount found in the leachates was only 0.31 mg or 0.18 % of the original dose.

Conclusions

These field and trough experiments suggest that there is little likelihood that much chlorfenvinphos will reach natural waters in the field as a result of leaching. It is more readily leached into the drainage water than over the surface of the soil, although the amount of rain falling on the treated soil was not very large either in the field or in the trough experiments. With higher rainfall surface run-off might be more important.

References

'Edwards, C . A., Thompson, A. R., & Eeynon, K. I., Rev.

Bevnon. K. I.. Davies. L.. & Elgar, K.. J. Sci. Fd Anric.,

sThompson, A. R., Edwards, C. A., Edwards, M. J., &

Beynon, K. I., Davies, L., & Stoydin, G., J. Sci. Fd Agric., Ecol. Biol. Sol., 1968, 5, 199 Beynon, K. I., Pesfic. Sci., 1970, 1, 174

, , - , . i966,'17, 167 1966,17, 162

Y. , Archs Envir. Hlfh, 1966, 12, 199 &Edwards, C. A., Residue Rev., 1966, 13, 83

M. J., Pesfic Sci., 1970, 1, 169

Lichtenstein, E. P., Schulz, K. R., Skrentry, R. F., & Tsukano,

Edwards, C. A., Thompson, A. R., Beynon, K. I., & Edwards,

8Beynon, K. I., Edwards, M. J. , Elgar, K., & Wright, A. N.,

9 Beynon, K. I., Edwards, M. J., Thompson, A. R., & Edwards, J. Sci. Fd Agric., 1968, 19, 302

C. A., Pesiic. Sci., 1971, 2, 5

Pestic. Sci., 1971, Vol. 2, January-February