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Organic Pesticides in the Environment Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 09/23/18. For personal use only.
Persistence of 2,6-Dichlorobenzonitrile in Aquatic Environments C H A R L E S C. VAN V A L I N U.S. Department of the Interior, Bureau of Sport Fisheries and Wildlife, Fish-Pesticide Research Laboratory, Denver, Colo. 80225
In two experiments 2,6-dichlorobenzonitrile was added to aquatic systems, and the residue levels were followed for about 6 months. A granular formulation applied to a farm pond at 0.6 p.p.m. produced highest residues in water and fish about 2 weeks following treatment whereas vegetation and soil samples had the highest levels within 1 or 2 days. Residues were still measurable after 188 days. In ponds treated with a wettable powder formulation at 10, 20, and 40 p.p.m., residues in water and fish were highest within 3 days after treatment. The concentration in water 11 days after treatment was about 2% of the three-day level. Fish whole-body residues dropped nearly as fast but were still measurable at 112 days.
Dichlobenil ( 2,6-dichlorobenzonitrile ) is used for weed control i n cranberry marshes, i n nursery stock and woody plants, for preemergent control i n crops, and for aquatic weed control. T h e acute toxicity of dichlobenil to fish has been measured at the Fish-Pesticide Research Laboratory i n Denver; the 2 4 - h o u r - L C values are 22 p.p.m. active ingredient to bluegills (Lepomis macrochirus Rafinesque) at 24°C. and 23 p.p.m. to rainbow trout (Salmo gairdneri Richardson) at 13°C. 50
The herbicidal effects have been documented, and there has been some work published regarding the persistence of dichlobenil in the soil. Barnsley and Rosher ( J ) measured the persistence of dichlobenil under both tropical and temperate conditions, using plant bioassay to measure residues. They found that dichlobenil disappeared rapidly, within a few days, when i t was applied to the soil surface but was not worked i n . However, when the chemical was incorporated i n the soil, it persisted 271
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ORGANIC PESTICIDES IN THE ENVIRONMENT
for several weeks. These persistence characteristics were attributed to the high vapor pressure of 5 Χ 10" mm. H g at 20°C. and the relatively low solubility i n water of 20 p.p.m. at 25°C. Massini (2) studied the movement of dichlobenil i n soils and i n plants. In addition to the vola tility and solubility effects, he found that it was strongly adsorbed on lignin, humic matter, and lipid material. A l y and Faust (3) investigated the physical, chemical, and biological factors which influence the persistence of 2,4-D compounds i n natural surface waters. They found that esters of 2,4-D i n aerobically incubated lake waters were hydrolyzed biologically to the free acid and correspond ing alcohol within 9 days and that 2,4-D was decomposed 8 1 - 8 5 % within 24 hours by lake muds after microbial adaptation. Ebeling (4) states that the disappearance of most pesticide residues appears to depend on first-order reaction kinetics, but unfortunately resi due data cannot be extrapolated from one environment or dosage range to another. Involved are the nature of the compound, absorption and metabolism by microorganisms, adsorption to mineral and organic col loids, absorption by higher organisms, chemical and photochemical alter ations, the temperature, and dispersal by air and water movement ( 5 , 6 ) . Sheets ( 5 ) , i n reviewing the disappearance of substituted urea herbi cides from soil, found that inactivation occurs under soil conditions favor able for the growth of microorganisms but takes place slowly or not at all in dry or autoclaved soil. Burschel and Freed ( 6 ) , reviewing work relat ing to 2,4-D and amitrole as well as monuron, state that the data indicate that ultimate breakdown is caused by microbiological attack. The persistence of dichlobenil i n an aquatic environment had not been studied, however. Therefore, studies were undertaken i n experi mental ponds at Tishomingo, Okla. and a farm pond near Denver. 4
Procedure and Methods
Eight 0.1-acre experimental ponds at Tishomingo were stocked with bluegills and were treated June 5, 1964. A wettable powder formulation was used which was calculated to yield dichlobenil concentrations of 0, 10, 20, and 40 p.p.m. Fish and water were sampled beginning 3 days following treatment. The final water sample was taken 85 days, and the final fish sample 112 days after treatment. Bottom soil samples beginning 1 month after treatment were supplemented by samples taken after the ponds were drained. The farm pond near Denver had a surface area of about two-thirds of an acre, with an average depth of 5 feet and a maximum depth of 11 feet. The fish present were predominantly bluegills, but there were also numerous largemouth bass, (Micropterus salmoides ( L a c e p e d e ) ) , green sunfish, (Lepomis cyanellus (Rafinesque)), and yellow perch (Perca fiavescens ( M i t c h i l l ) ) . Several kinds of weeds were present, principally a
22.
VAN V A L i N
2,6-Dichlorobenzonitrile
273
species of Chara, unidentified filamentous algae, and sago pondweed ( Potamogeton pectinatus L . ). The pond was treated by personnel of the Weed Investigations Laboratory of the Agricultural Research Service, U . S. Department of Agriculture on A p r i l 29, 1964, with a 4 % granular formulation of dichlobenil at the rate of 10 lb. active ingredient per surface acre, or about 0.6 p.p.m. Samples of fish, water, vegetation, and soil were collected before treatment and at scheduled intervals thereafter, beginning 6 hours after application and continuing through 188 days. A n additional soil sample was obtained on July 8, 1965. A l l samples obtained were analyzed for dichlobenil by modifications of procedures developed by the Thompson-Hayward Chemical C o . (7). Water samples were composites of portions taken from four différent points i n the ponds. The water was extracted by vigorously shaking 500 ml. in a 1000-ml. separatory funnel with solvent for 2 minutes for each of three portions—50, 25, and 25 ml.—of solvent. Benzene was used for most samples, although petroleum ether (30°-60°C.) was used for the first samples and worked equally well. The combined extracts were dried by passing "through a 10-gram column of anhydrous sodium sulfate, the volume of effluent was measured, and the dichlobenil was determined by electron capture gas chromatography. Pond bottom soil samples were composites of handfuls of soil taken from four different locations in the ponds and were extracted as obtained without draining or drying. The wet soil, weighing 100-150 grams, was extracted three times with a total of about 250 ml. of benzene by shaking the mixture vigorously i n a round-bottomed flask. After allowing the solid material to settle, the supernatant benzene was filtered. The filtrate was rinsed through a column consisting of 3-5 grams of anhydrous sodium sulfate on top of 10 grams of a 1:1 ( w / w ) MgO-Celite mixture i n a 20 χ 400-mm. chromatographic tube. After the benzene portions had drained through, the column was rinsed with about 20 m l . of benzene. The total effluent volume was measured, and the solution was analyzed by gas chromatography. Wet vegetation was ground in an Oster homogenizer with three times its weight of anhydrous sodium sulfate to obtain a free-flowing powder. The sample size used was usually about 40 grams. The ground mixture was extracted 5-7 hours with benzene i n a Soxhlet extractor, and the extract, followed b y 20 ml. of benzene, was passed through 10 grams of a 1:1 MgO-Celite mixture prior to gas chromatographic analysis. Because of the difficulty of obtaining a uniform wet weight for reporting, the results for soil and vegetation are reported on a dry weight basis. Frozen whole fish bodies were chopped into small pieces and ground in the Oster homogenizer with anhydrous sodium sulfate at the rate of one or two parts by weight of sodium sulfate per part of fresh tissue, depending on the dryness of the resulting mixture. T o obtain a freeflowing powder, the mixture was usually frozen and reground twice after the initial grinding. A sample of 100 grams of the mixture was extracted with benzene for 5-7 hours i n a Soxhlet extractor, and the extract was passed through a 10-gram MgO-Celite column. The column was rinsed with about 20 ml. of benzene, and the effluent volume was measured. A 50-ml. portion was treated with 1 ml. of concentrated sulfuric acid by shaking vigorously for 1 minute i n a 60-ml. separatory funnel. The acid
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ORGANIC PESTICIDES IN THE ENVIRONMENT
layer was separated and discarded, and the benzene solution was filtered through a 1-inch sodium sulfate pad. Analysis was by gas chromatography, with the results based on wet weight. For these analyses a Wilkens M o d e l 204 gas chromatograph equipped with electron capture detectors and 1-mv. recorder was used. Either of two column packing materials was used, D o w Corning Q F - 1 or D C - 1 1 ( 5 % w / w ) on Chromosorb W (60-80 mesh) i n 5-foot by % inch borosilicate glass columns. Injector, column, and detector temperatures were 170°, 164°, and 175°C, respectively. Nitrogen carrier gas flow was about 40 m l . per minute. Five to 10 /Jiter injections of the sample were made with a 10-^liter No. 701N Hamilton syringe. Dichlobenil was retained about 1.5 minutes on the Q F - 1 column and about 0.8 minute on the D C - 1 1 . Quantitation was based on recorder peak area measurements b y a Disc integrator. The volume of extract for the four types of sample ranged from about 125 to about 300 ml. Because of the high sensitivity of the electron capture detectors, it was not necessary to concentrate the samples except for the soil sample which was taken on July 8, 1965. The extract in this case was condensed to about 5 m l . i n a Kuderna-Danish evaporator. There was no detector response at the dichlobenil retention time with any of the pre-treatment samples. Recoveries of 9 0 % for soil, vegetation, and water and 8 3 % for fish were established by adding known amounts of dichlobenil to unprocessed samples and then carrying these samples through the entire process. Recovery i n the Kuderna-Danish concentration step was 9 0 % .
0
20
40
60 80 100 120 140 DAYS AFTER TREATMENT
Figure 1.
Dichlobenil in water
160 180
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VAN VALIN
2,6-Dichlorobenzonitrile
275
Results and Discussion
Analysis results from samples taken from only the 20-p.p.m.-treated Tishomingo ponds are considered i n this report. These are typical of the six treated ponds at Tishomingo; the patterns of herbicide build-up and removal are similar for all treatment levels, with quantitative differences proportional to the initial treatment. Owing to the properties of the formulations used and the characteristics of the ponds tested, the patterns of accumulation and decline of residues in the two experiments were considerably different, as illustrated in Figure 1. The concentration of dichlobenil in water in the Tishomingo ponds treated with wettable powder was highest in the sample taken 3 days following treatment. A level of 50 p.p.m. was measured, which was two and one-half times treatment level. W e cannot explain this anomalous level; error in treatment does not appear likely, nor does stratification or localization of the dichlobenil within the pond, especially since the water sample was a composite of portions taken at four different points. The only possibility that seems worth considering is that some of the powder from the formulation could have been floating at the surface where it could easily have become part of the sample. The concentration of dissolved dichlobenil declined rapidly so that the 11-day levels averaged about 2 % of the 3-day levels. In contrast, the highest concentration in the farm pond near Denver was measured nearly 3 weeks after treatment, at a level of 0.43 p.p.m. or about three-fourths of the theoretical maximum. Presumably, this lag in peaking was caused by the slow dissolution of the granular formulation. The much more gradual decline of the dissolved dichlobenil i n this pond was probably caused by pond characteristics, such as temperature and bacterial activity. The last water samples from the Tishomingo ponds, taken 85 days after treatment, showed that the residue level had decreased to 1.23 p.p.b. Dichlobenil remained in the Denver pond 188 days following treatment at a level of 1.05 p.p.b. A heavy rainstorm on July 30, 1964, one day before the 93-day sample was collected from the Denver pond, probably caused the dilution apparent in this and succeeding water samples. There was some overflow observed. After the rainstorm, water samples were collected from the pond below the dichlobenil-treated pond by personnel of the Weed Investigations Laboratory. Their analyses of these samples showed 0.03 p.p.m., indicating, on the basis of water volumes in the two ponds, that a considerable portion (perhaps as much as one-third) of the water in the dichlobenil-treated pond had been exchanged. Figure 2 shows a pattern of residues in fish similar to that for water. Fish in the Tishomingo ponds treated with 20 p.p.m. of the wettable powder quickly absorbed high amounts of the herbicide; whole-body
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ORGANIC PESTICIDES IN T H E ENVIRONMENT
DAYS AFTER Figure 2.
TREATMENT
Dichlobenil in fish
dichlobenil residues average 98 p.p.m. 3 days after treatment, twice the amount measured i n water. The decline was rapid thereafter, similar to the water samples. Residue accumulation took place much less quickly in fish i n the granular formulation-treated pond. Whole-body residues increased during the first 2 weeks of exposure to above 6 p.p.m., and this level apparently persisted for about 3 weeks since samples taken 35 days following treatment contained a level of 6 p.p.m. A t this date the d i chlobenil concentration i n water had declined to about one-half the maximum level, and the fish whole-body residues were over 20 times the
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277
2,6-Dichlorobenzonitnle
VAN VALIN
concentration i n water. Bluegill and green sunfish residue levels were approximately equal and consistently about 5 0 % higher than those found in bass or perch. Pond m u d at Tishomingo was first sampled about 1 month after treatment. Residue levels then were about 0.2 p.p.m., and this concentration gradually declined until the ponds were drained i n October. Dichlobenil then was present at about 0.03 p.p.m. The residue pattern for soil from the granule-treated pond is shown in Figure 3. Predictably, concentrations are highest within the first few
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0.6 R RM. GRANULAR-DENVER
4 2 0
20
40
Figure 3.
JL
=4.
60 80 100 120 140 DAYS AFTER TREATMENT
160
180
Dichlobenil in pond bottom mud
days, with the peak concentration of almost 13 p.p.m. found i n a sample taken 2 days after treatment. About half that level occurred i n the sample taken 2 days later, but the decline thereafter was more gradual. The last soil sample, taken over 14 months after treatment, contained 0.08 p.p.b. The high treatment levels i n the Tishomingo ponds completely elim inated any plant growth. The 0.6-p.p.m. treatment i n the Denver farm pond killed a l l vegetation except the filamentous algae, and this was severely inhibited for several weeks. The results illustrated i n Figure 4 were obtained from the filamentous algae. Chara samples were obtained i n the first 8 days following treatment and were close to the algae i n residue amounts. The peak concentration measured for the algae was i n the sample taken one day after treatment, with the surprising level of
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ORGANIC PESTICIDES IN THE ENVIRONMENT
DAYS AFTER Figure 4.
TREATMENT
Dichlobenil in algae
over 500 p.p.m. W i t h i n the next 7 days the residue level dropped to about 25 p.p.m. Following this sharp decline was the more gradual drop i n residue concentration, typical of the patterns for water, fish tissue, and soil as well. Numerous samples taken from the farm pond were analyzed for 2,6-dichlorobenzoic acid ( 7 ) , as well as for dichlobenil. Although the presence of the benzoic acid derivative was expected as a metabolite, none was found. Interestingly, Massini (2) d i d detect one metabolite of dichlobenil but proved that it was not 2,6-dichlorobenzoic acid.
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VAN VALIN
2,6~Dichlorobenzonitnle
279
Acknowledgment T h e author gratefully acknowledges the assistance of Oliver B . Cope, W . R. Bridges, Herman Sanders, Joseph M c C r a r e n , and others of the staff of the Fish-Pesticide Research Laboratory, and Peter A . Frank of the Weed
Investigations Laboratory, Agricultural Research Service, U . S.
Department of Agriculture. Literature
Cited
Barnsley, G. E., Rosher, P. H . , Weed Research 1, 147 (1961). Massini, P., Weed Research 1, 142 (1961). Aly, Ο. M . , Faust, S. D., J. Agr. Food Chem. 12(6), 541 (1964). Ebeling, W . , "Residue Reviews," Vol. 3, p. 116, Academic Press, Ν. Y., 1963. (5) Sheets, T . J., J. Agr. Food Chem. 12(1), 30 (1964). (6) Burschel, P., Freed, V . H . , Weeds 7(2), 157 (1959). (7) Shadbolt, C. Α., Thompson-Hayward Chemical Company, Kansas City, Kansas, private communication.
(1) (2) (3) (4)
RECEIVED October 13, 1965.
