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Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Enhanced degradation of carbofuran in pacific northwest soils a
Louis W. Getzin & Carl H. Shanks Jr.
a
a
Research & Extension Center , Washington State University‐Puyallup , Puyallup, Washington, 98371–4998 Published online: 21 Nov 2008.
To cite this article: Louis W. Getzin & Carl H. Shanks Jr. (1990) Enhanced degradation of carbofuran in pacific northwest soils, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 25:4, 433-446 To link to this article: http://dx.doi.org/10.1080/03601239009372699
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J. ENVIRON. SCI. HEALTH, B25(4), 433-446 (1990)
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ENHANCED DEGRADATION OF CARBOFURAN IN PACIFIC NORTHWEST SOILS
KEYWORDS: carbofuran, soil insecticide, enhanced degradation, soil microorganisms Louis W. Getzin and Carl H. Shanks, Jr. 1 Washington State University-Puyallup Research & Extension Center Puyallup, Washington 98371-4998
ABSTRACT Persistence of
14 C-carbonyl carbofuran was measured in Pacific Northwest
soils that had received 1-14 applications of the insecticide for root weevil control on perennial crops. Insecticide decay curves were obtained in nonautoclaved soil and several autoclaved soil samples from previously-treated fields and in nonautoclaved soils from paired control sites not previously treated with carbofuran. The insecticide usually degraded faster in soil from previously-treated fields than in soil from corresponding control fields. Among 26 previously-treated fields, the pseudo half-life (time for 50% loss) of carbofuran was < one wk in 11 soils, 1-3 wks in 8 soils and > 4 wks in the remaining soils. Among the nontreated control fields the pseudo half-life was > than 2 wks in all cases and > than 15 wks in 5 of the soils. The carbofuran decay curve always possessed an initial lag phase where soil mixing enhanced insecticide decline. Carbofuran degraded very slowly in autoclaved soil 1 Send reprint requests to Carl H. Shanks, Jr., Washington State UniversityVancouver, Research & Extension Unit, 1919 N. E. 78th St., Vancouver, WA 98665-9752 433 Copyright© 1990 by Marcel Dekker, Inc.
434
GETZIN AND SHANKS
samples. The half-life of carbofuran exceeded 16 wk in all autoclaved soils tested and in most instances 85-90% of the original dosage remained when the tests were terminated 112 days after treatment. These results provided evidence that many of the soils which received applications of carbofuran over the past several years have
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developed a capacity to degrade carbofuran very rapidly.
INTRODUCTION Accelerated degradation of carbofuran has been reported in the mid-West region of the United States where vast corn acreages are treated annually to control i
Diabrotica
corn rootworms and in Canada and the United Kingdom where
carbofuran is used to control root maggots attacking vegetables (Felsot et al. 1982, 1985; Harris et al. 1984, 1988; Suett 1987). The shortened residual life of the pesticide is due to enhanced microbial activity (Felsot et al. 1981; Kaufman & Edwards 1983; Harris et al. 1984). This subject has been reviewed by Felsot (1989). Often target pests are not controlled where enhanced biodegradation occurs. In the Pacific Northwest, carbofuran has been used as a soil treatment against root weevils (Otiorhynchus
spp.) that attack several perennial crops,
including strawberries, raspberries, cranberries, mint and ornamentals. Carbofuran is the only chemical that controls both adults and established infestations of larvae. Because the target crops are long-term perennials, annual soil applications and a lengthy history of carbofuran use are common. Carbofuran has been applied annually to some fields for 8 years or more. Generally, the treatments have been effective but in recent years there have been an increasing number of control failures. The objective of this study was to determine if enhanced degradation of carbofuran in Pacific Northwest soils.
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TABLE 1 Sources, Crops, Carbofuran Use Histories, and Sample Collection Dates for Soils Studied for Accelerated Degradation of Carbofuran.
a
Soil No.
Farm
Location
Crop
No. of Applications8
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Abshire Dibkey Lamni WSU-Long Beach Krahmer Duyck Jesse Reersley Rose Vernon Kruse WSU-Vancouver Saranto Beaudoin Philbrook Sakuma Boxx Chilton Hayberry Peters Matlock Picha Biringer Weisopt Hayberry Hayberry
Grays Harbor Co., Wash. Grays Harbor Co., Wash. Grays Harbor Co., Wash. Pacific Co., Wash. Washington Co., Ore. Washington Co., Ore. Washington Co., Ore. Lane Co., Ore. Lane Co., Ore. Cloverdale, Br. Col. Skagit Co., Wash. Clark Co., Wash. Walla Walla, Wash. Clark Co., Wash. Clark Co., Wash. Skagit Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash. Kankakee Co., 111. Pierce Co., Wash. Pierce Co., Wash. Snohomish Co., Wash. Snohomish Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash.
Cranberry Cranberry Cranberry Cranberry Strawberry Strawberry Strawberry Mint Hint Vegetables Strawberry Strawberry Alfalfa Strawberry Raspberry Strawberry Strawberry Raspberry Strawberry Corn Strawberry Strawberry Strawberry Strawberry Raspberry Strawberry
9 12 8 9 4 4 3 . 3 5 6 1 14 6 4 2 3 2 2 2 3 2 2 3 2 2 3
Years applied
Date soil sample collected
1978-83 1978-83 1980-83 1977-83 1980-83 1980-83 1981-83 1981-83 1980-83 1978-83 1982 1976-83 1978-83 1981-84 1983-84 1981-83 1982-83 1983-84 1982-83 1978-81 1983-84 1983-84 1982-84 1982-83 1983-84 1982-84
Har., 1984 Har., 1984 Har., 1984 Mar., 1984 Har., 1984 Har., 1984 Har., 1984 Har., 1984 Har., 1984 Apr., 1984 Apr., 1984 Hov., 1984 Apr., 1984 Nov., 1984 Nov., 1984 Apr., 1984 Hay, 1984 Hay, 1984 Hay, 1984 Jan., 1985 Jan., 1985 Jan., 1985 Feb., 1985 Feb., 1985 Hay, 1985 Hay, 1985
Application rates of 2 lb. Al/acre to soil except for Soil no. 12 (1.5 lb/A), Soil no. 15 (foliar 0.75 lb./A.) and Soil no. 22 (1 lb./A).
P! S!
o a a
H
o O
a w o
436
GETZIN AND SHANKS
MATERIALS AND METHODS Carbofuran persistence was measured in soils collected from 26 locations in 1984 and early 1985 (Table 1). Two soil samples were taken at each location. The "treated" sample was collected from a field with a documented history of carbofuran
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use. A second sample, the non-treated "control" was collected from an adjacent or nearby field that had no known history of carbofuran use. Most of the fields with a history of carbofuran use had established plantings of strawberries, raspberries, cranberries, or mint. The number of previous carbofuran treatments ranged from 1 to 14, A composite sample consisting of nine cores (10 cm deep x 10.4 cm diam.) was taken from each treated field with a cylindrical soil sampler. A composite of five cores was taken from the adjacent control site. Precautions were taken to minimize cross-contamination of soil samples. Control areas were always sampled first at each location and the sampling tool was washed free of soil and then soaked in a solution of either sodium hypochlorite or a commercial antiseptic agent (0-SYL, National Laboratories, Montvale, New Jersey) between locations. Composite samples were transported to the laboratory, partially dried to a workable condition when necessary, screened through a 3.2-mm mesh sieve, blended, and stored in double 1.25-mil plastic bags at 5°C. All sieving equipment was washed and soaked in a solution of the commercial antiseptic agent between samples. Table 1 gives the source, location, cropping system, and carbofuran use history of the treated fields. Soil moisture equivalents were determined by the method of Briggs and McLane (1907). Organic matter was measured by the method of Walkley and Black (1934). Soil pH was determined by mixing 10 g of dry soil with 20 ml of distilled water, and measuring pH after 30 minutes with a pH meter. A mechanical analysis
ENHANCED DEGRADATION OF CARBOFURAN
437
of each soil was conducted by methods of Boyoucos (1936) after organic matter _ was digested with hydrogen peroxide. The properties of each soil are shown in Table 2. 14 C-carbonyl carbofuran (14.36 mCi/mM) was provided by FMC
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Corporation, Princeton, NJ. On receipt, the product was partitioned between water and chloroform to a radiochemical purity of 98%. Reference standards of nonradioactive carbofuran, 3-hydroxy carbofuran and 3-keto-carbofuran, and a commercial flowable concentrate formulation of carbofuran (Furadan 4F) also were obtained from FMC Corporation. Scintillation cocktail was prepared by dissolving 23 g of premixed scintillators (OMNIFLUOR, New England Nuclear, Boston, MA) in 4 liters of toluene. Ten ml of water containing iu,Ci of
C-carbofuran and 4 mg of non-
radioactive insecticide (Furadan 4F) were sprayed with DeViibis atomizer onto 400 cc of moist soil in an open faced 3.8-liter rotating blender. Additional water was applied to bring the water content of the soil to its soil moisture equivalent (Briggs and McLane 1907). Persistence of
14
C-carbofuran was measured in soils that were mixed at
intervals during the post-treatment incubation period, in soils that were incubated without mixing, and in soil samples from a few treated fields that were autoclaved to destroy microorganisms. To kill microorganisms, 400-cc volumes of moist soil were autoclaved at 15 psi for 1 hr. Autoclaved soil was sterile initially, but became contaminated with airborne spores during application of
14
C-carbofuran and
subsequent handling procedures. To determine persistence of carbofuran in soil that was not mixed during post-treatment incubation, 20-cc volumes of treated soil were weighed Into 60-cc glass bottles. The bottles were stoppered with plastic foam
438
GETZIN AND SHANKS
TABLE 2 Some Chemical and Physical Properties of Soils Used in This Study. Soil Mechanical analysis b _ c d PH no. SME O.M. C.E.C. % sand % silt % clay
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3C 3T 4C 4T 5C 5T 6C 6T 7C 7T 8C 8T 9C 9T 10C 10T 11C 11T 12C 12T 13C 13T 14C 14T 15C 15T 16C 16T 17C 17T 18C 18T 19C 19T 20C 20T 21C 21T 22C 22T
23C 23T 24C 24T 25C 25T 26C 26T 27C 27T 28C 28T
31 30 31 26 34 34 25 22 23 23 24 24 28 26 29 25 28 28 150 85 42 39 20 18 22 18 32 28 26
24 26 33 31 30 34 34 25 26 28 18 22 27 29 35 39 37 34 35 32 30 22 30
4.9 5.2 4.9 5.1 4.8 4.8 4.9 5.3 6.7 5.3 6.0 4.7 6.2 5.9 6.7 6.1 6.0 5.4 5.2 5.2 6.0 6.1 5.9 6.1 7.4 7.4 5.3 5.3 6.0 5.1 6.0 6.5 5.9 6.0 5.8 5.9 6.3 6.2 7.9 6.6 5.4 5.6 5.3 5.9 5.6 5.9 6.1 5.4 5.8 4.7 5.6
6.0
5.1 3.7 5.1 2.0 1.9 5.0 7.6 1.5 2.0 2.0 3.3 3.2 4.6 3.3 3.9 2.7 5.5 4.0
56.8 45.0 8.7 6.4 3.0 1.1 2.3 1.1 7.9 6.3 3.1 3.1 2.9 1.6 3.9 3.5 4.0 3.9 3.1 3.3 5.3 2.1 1.6 2.5 2.3 3.2 6.0 5.8 5.0 4.4 5.0 5.5 4.2 5.2
18.5 16.7 18.5 7.4 7.3
18.0 18.2 8.8
13.5 14.5 19.2 19.0 18.2 14.0 32.0 27.5 22.0 16.5 107.5 72.5 33.7 27.5 16.0 16.0 12.5 18.5 33.3 29.5 20.0 20.5 12.8 16.8 19.5 17.5 20.0 25.0 12.5 13.3 36.8 20.0 9.3
13.5 12.5 16.5 21.0 22.0 18.0 17.0 21.2 20.4 13.9 20.8
97 98 97 98 98 97 92 97 25 21 21 23 19 19 19 25 13 13 . .
9 12 64 67 41 58 44 41 42 45 49 41 56 60 49 49 59 62 32 49 66 57 24 13 10 17 27 17 49 52 68 51
3 2 3 2 2 3 7 3 55 58 52 53 59 60 64 41 56 62 . 44 44 74 21 42 31 38 41 37 36 40 42 32 29 40 41 28 26 42 28 29 36 57 64 57 51 55 57 33 33 22 38
0 0 0 0 0 0 . 1 0 20 21 27 24 22 21 17 34 31 25 . 47 44 12 12 17 11 1B 18 21 19 11 17 12 11 11 10 13 12 26 23 5 7 19 23 33 32 18 26 18 15 10 11
Soil
sand sand sand sand sand sand sand sand silt loam silt loam silt loam silt loam silt loam silt loam silt loam clay loam silty clay loam silt loam organic organic silty clay silty clay sandy loam sandy loam loam sandy loam loam loam loam loam loam loam sandy loam sandy loam loam loam sandy loam sandy loam loam sandy clay loam sandy loam sandy loam silt loam silt loam silty clay loam silty clay loam silt loam silt loam loam loam sandy loam loam
T = site with previous carbofuran use history; C = control site with no history of carbofuran use Soil moisture equivalent. j Organic matter; ; Cation exchange capacity (meq/100 g of soil);
b
ENHANCED DEGRADATION OF CARBOFURAN
A39
culture tube plugs, placed on trays in 1.25-mil plastic bags containing a small amount of water to maintain a water vapor saturated atmosphere, and incubated undisturbed. To determine persistence of carbofuran in soil that was mixed during laboratory incubation, each 400-cc volume of treated soil was placed in a double
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1.25-mil plastic bag. The soil was blended in the bag for ca 30 sec each time a subsample was removed for analysis. All treated samples of soil were incubated in the dark at 20 ± 1 °C. Most soil treatments were duplicated, some were replicated 4 times. Immediately after treatment and at selected intervals thereafter, samples of each treated soil were analyzed for
14 C-carbofuran. Sampling was conducted at 1-4
day intervals, depending upon rapidity of degradation, for the first week, weekly until after 4 weeks, and biweekly until 16 weeks had elapsed. For non-mixed samples, the soil from each bottle was transferred to a 250-ml polyethylene centrifuge bottle with 100 ml of extracting solvent (90% acetone and 10% 0.25N HC1). For soils that were bulk-stored in plastic bags for mixing during the incubation period, a 20-cc volume of soil was weighed out from the plastic bag with a disposable plastic spoon and placed in a 250-ml polyethylene bottle with 100 ml of solvent. The bottles were stoppered, agitated on a reciprocating shaker for 45 min and then centrifuged at 1000 x g for 10 min. Five ml of supernatant were transferred to a 25-ml screw cap centrifuge tube. The solvent was evaporated to near dryness, and the residue was partitioned between 5-ml volumes of methylene chloride and water to separate
14 C-
carbofuran from small amounts of water soluble radioactivity in the acetone:water extract. After centrifuging at 1000 x g for 5 min, 2 ml of the methylene chloride layer were transferred to a glass scintillation vial, the solvent was evaporated, and the residue was dissolved in 8 ml of scintillation cocktail. Radioactivity was counted in a TM Analytic Model 6895 Automatic Liquid Scintillation System.
440
GETZIN AND SHANKS
Radioactivity in methylene chloride from selected samples also was separated with thin-layer chromatography using etherhexane (3:1) as the developing solvent (Getzin 1973) to determine if radioactive components other than carbofuran were present.
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RESULTS Texture of the soils used varied from almost pure sands containing some organic matter (cranberry sites) to silty clay loams containing over 30% clay (Table 2). An organic soil (Soil 12) also was included. Soil acidity generally ranged from pH 5 to pH 6.5 although three soils (15C, 15T and 22C) were above pH 7.0. Soil pH readings shown in Table 2 were taken at the beginning of an experiment. Usually soil pH declined 0.2 to 0.4 units during the course of the incubation period. Organic matter content generally ranged from 2-6% with the exception of Soil 12 which contained approximately 50% organic matter. Moisture contents of treated soils decreased only slightly during the course of the experiments. Adjustments were made in weights of samples removed for extraction from bulk volumes of test soils (mixed treatments) to compensate for the slight loss of water. Recoveries of total radioactivity from soil averaged 101 ± 3 % when soil was fortified with known amounts of
C-carbofuran. Extracted
C was converted to
percentage of carbofuran recovered. Initial recovery of carbofuran from all soils was 97 ± 2%. Previous studies with other insecticides indicated that about 5% loss of insecticide occurred while the chemical is being sprayed on the soil. Thin-layer chromatographic separation of solvent-partitioned extracts from selected soil samples gave a single major compound. Exceptions occurred when recovery radioactivity declined to < 5% of the original application. Radioactivity that did not correspond to the R, of authentic carbofuran was present either as a spot at the origin, or as a diffuse streak between the origin and the parent compound. This
ENHANCED DEGRADATION OF CARBOFURAN
441
limited chromatographic survey indicated that the extraction, solvent partition, and radioassay procedures employed were satisfactory for monitoring persistence of parent carbofuran in soils. Carbofuran persistence was expressed as a pseudo half-life, i.e., the time for
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50% loss of the parent compound, (Table 3) determined by 'best fit' observations (Hamaker 1972). Because of the shape of the persistence curves and the limited number of data points during critical insecticide decay intervals for some soils, mathematical treatment of the data did not give meaningful results. Carbofuran persistence varied greatly between soils. For 22 of the 26 locations, the insecticide degraded faster in samples from previously-treated fields than in samples from paired control sites that had no history of carbofuran use whether the samples were mixed or not. Exceptions were Soils 8, 11, 15, and 27 where similar degradation rates were observed for previously-treated fields and the paired controls in mixed and/or non-mixed soils. Large differences in decay rates were also observed between soils from the fields with a history of previous carbofuran use. The time for 50% loss of insecticide in previously treated fields ranged from 2.5 days to > 70 days. Pseudo half-lives of 9 days or less were recorded for samples from 15 of the 26 sites surveyed. Substantial variation of decay rates also was found in samples from fields that had no history of previous carbofuran use. Pseudo half-lives of 15 to 28 days were found in samples from 15 controls fields. In 9 mixed control soils and in 21 nonmixed control soils the pseudo half-life exceeded 70 days. The shortest pseudo-life of carbofuran in mixed control soil was 12 days (Soil 19). The shortest pseudo halflife for non-mixed control soils was 23 days (Soils 19 and 23). Initial lag phases of three days or more preceded rapid decline rates in a large number of soils from both treated and non-treated fields. Seldom did the insecticide decline curves exhibit classic 1st-order rate behavior. Lag patterns are
442
GETZIN AND SHANKS
TABLE 3 a
Pseudo Half-lives of
14
C-carbofuran in Soils With and Without a Carbofuran-Use History. Pseudo half-life of carbofuran (days)
Mixed soil
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Soil
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
C
T
28 28*
40 21* 22*
8* 6 12* 34 6.5 6.5 4
(70)
7.5*
27*
30*
(53) (81)
25.5* (64) 16 74
(68) 89* 19* 12*
(59) 19* 19* 15* 25*
(63) (61) 18* 19*
11.5* 25* 2.5 18* 4 20 8* 4 7* 9* 7*
6.5* 6.5* 4 32* 16 4
b
Non-mixed soil A
C
T
73 73
9.5*
(90)
(94) (82) (61)
70
(87)
100
102
9.5*
(62)
63 2.5 72 3 70 8* 4 8*
35 70
(62) (75)
e*
70
(62) (56)
40
(63) (92)
(90)
6.5 19* 37 6.5 4
(51) (73) (88)
A
91 112 23*
(54) (56*)I
(94) (87) (65) (86) (79)
10.5*
(79) (87)
36* 23*
(83)
3.5
5.5* 5.5* (70)
(56)
73
72 91
19.5
(65)
(82)
6*
(85) (88) (87)
4
14 Pseudo half-life is the time for 50% loss of C-carbofuran in soil incubated at 20° C. Numbers in parentheses indicate percentage of original carbofuran remaining when study was terminated at 112 days (pseudo half-life was > 112 days). Asterisks indicate carbofuran degradation was preceded by an initial lag phase of 3 days or more: T = soil from field previously treated with carbofuran; A = autoclaved soil from treated site; C = soil from non-treated control site.
characteristic of the induction of microbiai populations with a capacity to degrade the insecticide (Alexander 1981). Carbofuran persistence in autoclaved soil was measured to determine rates of nonmicrobial degradation, and to monitor the extent of cross-contamination that occurred during insecticide treatment in the laboratory and subsequent handling
ENHANCED DEGRADATION OF CARBOFURAN
443
procedures. Although precautions were taken to prevent it, some crosscontamination did occur for treatments where the soil was bulk stored in plastic bags and mixed frequently during the incubation period. Cross-contamination was indicated when the decline curves for individual replicates of a treatment greatly
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differed. An example of where contamination probably occurred in both replicates of an autoclaved treatment is Soil 19A, which had a pseudo half-life of only 70 days compared to over 112 days for all other autoclaved samples. Because no contamination appeared in non-mixed treatment tests, it is possible that contamination occurred during the frequent handling of the bulk soil samples after the soil was treated with radio-labeled carbofuran. Contamination also appeared in single replicates of several mixed control soils. Differences in the decline curve between replications occurred after the 8-week sampling period for control Soils 5, 25, and 26. When the decline curves for both replicates of a treatment exhibited an extended lag phase followed by a rapid decline of insecticide, the experiment was repeated. Carbofuran was highly persistent in most autoclaved soils. The time for 50% loss of insecticide exceeded 112 days in all instances except for the mixed treatment in Soil 19. Excluding Soil 19A, the amount of the insecticide remaining in autoclaved soil samples at 112 days ranged from 61 to 94% of the original application dosage. The fastest breakdown occurred in autoclaved samples of Soil 15, which was the soil with the highest pH.
DISCUSSION The finding that carbofuran usually degraded much faster in soil samples taken from fields with a history of carbofuran use than in soil samples taken from adjacent fields with no history of carbofuran use suggests that enhanced
444
GETZIN AND SHANKS
degradation occurs in the Pacific Northwest. Enhanced degradation developed with as few as one or two applications of carbofuran, which was also observed by Harris et al. (1984, 1988). In the laboratory tests, accelerated degradation developed during the course of an initial treatment in some soil samples not previously exposed
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to carbofuran treatment. Similar observations have been made by Harris et al. (1988) and Dzantor and Felsot (1989). Since frequent blending of treated soil accelerated degradation in some laboratory samples, cultivation and other mechanical disturbances alone may enhance the rate of degradation. Harris et al. (1984) observed significantly faster degradation in soils that were mixed than in soils that were unmixed and they concluded that mixing efficiently distributed active microorganisms throughout the soil. Soils from fields with a natural pH lower than 5.8 did not show evidence of rapid microbial degradation of carbofuran in studies by Read (1986). Walker et al. (1986) observed slow degradation of the fungicides iprodione and vinclozolin in soil with a pH of 5.0 and suggested that the microorganisms responsible for degradation of the chemicals was inhibited by the low pH. In our studies, soils with a pH less than 5.0, e.g. Soils 3-5 and 27, showed definite enhanced degradation of carbofuran after the fields had been treated with that chemical. The slow decay rate of carbofuran in autoclaved soil suggests that the insecticide will persist for long periods in subsurface soil zones with low microbial activity. This may influence the potential for ground water contamination in areas with rainfall, coarse-textured soils and shallow water tables. In conclusion rapid loss of carbofuran in some soils suggests that enhanced i
degradation may account for the poor insect control that has been reported for several locations in the Pacific Northwest. Field studies that combine efficacy tests with insecticide residue tests are needed to determine if enhanced degradation is actually responsible for these insect control failures.
ENHANCED DEGRADATION OF CARBOFURAN
445
ACKNOWLEDGMENTS The assistance of Darrell Barstow in the conduct of this research is gratefully acknowledged. Thanks are due also to A. S. Felsot and C. R. Harris for their critical reviews of the manuscript. Research was conducted under Projects 0741 and 1957,
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Washington State. University, College of Agriculture and Home Economics, Research Center, Pullman, Wash. 99164.
REFERENCES CITED Alexander, M., Science 211, 132-138 (1981). Bouyoucos, G.J., Soil Sci. 42, 225-229 (1936). Briggs, L.J. and McLane, J.W., USDA Soils Bureau Bull. 45 (1907). Dzantor, E.K. and Felsot, A.S., J. Environ. Sci. Hlth. B24, 569-587 (1989). Felsot, A.S., Annu. Rev. Entomol. 34, 453-476 (1989). Felsot, A., Maddox, J.V., and Bruce, W., Bull. Environ. Contam. Toxicol. 26, 781788 (1981). Felsot, A.S., Steffey, K.L., Levine, E., and Wilson, J.G., J. Econ. Entomol. 78, 45-52 (1985). Felsot, A.S., Wilson, J.G., Kuhlman, D.E. and Steffey, K.L., J. Econ. Entomol. 75, 1098-1103 (1982). Getzln, L.W., Environ. Entomol. 2, 461-467 (1973).
Hamaker, J.W. IN Organic Chemicals in the Soil Environment, Vol. I. C. A. I. Goring and J.W. Hamaker [eds.], Marcel Dekker, New York, pp. 253-340 (1972). Harris, C.R., Chapman, R.A., Harris, C., and Tu, C.M., J. Environ. Sci. Hlth. B19, 111 (1984). Harris, C.R., Chapman, R.A., Morris, R.F., and Stevenson, A.B., J. Environ. Sci. Hlth. B23. 301-316 (1988). Harris, C.R., Chapman, R.A., Tolman, J.H., Moy, P., Henning, K., and Harris, C , J. Environ. Sci.. Hlth B22, 1-32 (1988).
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Kauffman, D.D. and Edwards, D.F. IN Pesticide Chemistry:Human Welfare and the Environment. J. Miyamoto & P. C. Kearny [eds.], Pergamon, Oxford, UK, pp. 173-182 (1983). Suett, D.L., Crop Protection g: 371-378 (1987).
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Walkey, A. and Black, I.A., Soil Sci. 27, 29-38 (1934).
Received: April 10, 1990
Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesb20
Enhanced degradation of carbofuran in pacific northwest soils a
Louis W. Getzin & Carl H. Shanks Jr.
a
a
Research & Extension Center , Washington State University‐Puyallup , Puyallup, Washington, 98371–4998 Published online: 21 Nov 2008.
To cite this article: Louis W. Getzin & Carl H. Shanks Jr. (1990) Enhanced degradation of carbofuran in pacific northwest soils, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 25:4, 433-446 To link to this article: http://dx.doi.org/10.1080/03601239009372699
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J. ENVIRON. SCI. HEALTH, B25(4), 433-446 (1990)
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ENHANCED DEGRADATION OF CARBOFURAN IN PACIFIC NORTHWEST SOILS
KEYWORDS: carbofuran, soil insecticide, enhanced degradation, soil microorganisms Louis W. Getzin and Carl H. Shanks, Jr. 1 Washington State University-Puyallup Research & Extension Center Puyallup, Washington 98371-4998
ABSTRACT Persistence of
14 C-carbonyl carbofuran was measured in Pacific Northwest
soils that had received 1-14 applications of the insecticide for root weevil control on perennial crops. Insecticide decay curves were obtained in nonautoclaved soil and several autoclaved soil samples from previously-treated fields and in nonautoclaved soils from paired control sites not previously treated with carbofuran. The insecticide usually degraded faster in soil from previously-treated fields than in soil from corresponding control fields. Among 26 previously-treated fields, the pseudo half-life (time for 50% loss) of carbofuran was < one wk in 11 soils, 1-3 wks in 8 soils and > 4 wks in the remaining soils. Among the nontreated control fields the pseudo half-life was > than 2 wks in all cases and > than 15 wks in 5 of the soils. The carbofuran decay curve always possessed an initial lag phase where soil mixing enhanced insecticide decline. Carbofuran degraded very slowly in autoclaved soil 1 Send reprint requests to Carl H. Shanks, Jr., Washington State UniversityVancouver, Research & Extension Unit, 1919 N. E. 78th St., Vancouver, WA 98665-9752 433 Copyright© 1990 by Marcel Dekker, Inc.
434
GETZIN AND SHANKS
samples. The half-life of carbofuran exceeded 16 wk in all autoclaved soils tested and in most instances 85-90% of the original dosage remained when the tests were terminated 112 days after treatment. These results provided evidence that many of the soils which received applications of carbofuran over the past several years have
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developed a capacity to degrade carbofuran very rapidly.
INTRODUCTION Accelerated degradation of carbofuran has been reported in the mid-West region of the United States where vast corn acreages are treated annually to control i
Diabrotica
corn rootworms and in Canada and the United Kingdom where
carbofuran is used to control root maggots attacking vegetables (Felsot et al. 1982, 1985; Harris et al. 1984, 1988; Suett 1987). The shortened residual life of the pesticide is due to enhanced microbial activity (Felsot et al. 1981; Kaufman & Edwards 1983; Harris et al. 1984). This subject has been reviewed by Felsot (1989). Often target pests are not controlled where enhanced biodegradation occurs. In the Pacific Northwest, carbofuran has been used as a soil treatment against root weevils (Otiorhynchus
spp.) that attack several perennial crops,
including strawberries, raspberries, cranberries, mint and ornamentals. Carbofuran is the only chemical that controls both adults and established infestations of larvae. Because the target crops are long-term perennials, annual soil applications and a lengthy history of carbofuran use are common. Carbofuran has been applied annually to some fields for 8 years or more. Generally, the treatments have been effective but in recent years there have been an increasing number of control failures. The objective of this study was to determine if enhanced degradation of carbofuran in Pacific Northwest soils.
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TABLE 1 Sources, Crops, Carbofuran Use Histories, and Sample Collection Dates for Soils Studied for Accelerated Degradation of Carbofuran.
a
Soil No.
Farm
Location
Crop
No. of Applications8
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Abshire Dibkey Lamni WSU-Long Beach Krahmer Duyck Jesse Reersley Rose Vernon Kruse WSU-Vancouver Saranto Beaudoin Philbrook Sakuma Boxx Chilton Hayberry Peters Matlock Picha Biringer Weisopt Hayberry Hayberry
Grays Harbor Co., Wash. Grays Harbor Co., Wash. Grays Harbor Co., Wash. Pacific Co., Wash. Washington Co., Ore. Washington Co., Ore. Washington Co., Ore. Lane Co., Ore. Lane Co., Ore. Cloverdale, Br. Col. Skagit Co., Wash. Clark Co., Wash. Walla Walla, Wash. Clark Co., Wash. Clark Co., Wash. Skagit Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash. Kankakee Co., 111. Pierce Co., Wash. Pierce Co., Wash. Snohomish Co., Wash. Snohomish Co., Wash. Whatcom Co., Wash. Whatcom Co., Wash.
Cranberry Cranberry Cranberry Cranberry Strawberry Strawberry Strawberry Mint Hint Vegetables Strawberry Strawberry Alfalfa Strawberry Raspberry Strawberry Strawberry Raspberry Strawberry Corn Strawberry Strawberry Strawberry Strawberry Raspberry Strawberry
9 12 8 9 4 4 3 . 3 5 6 1 14 6 4 2 3 2 2 2 3 2 2 3 2 2 3
Years applied
Date soil sample collected
1978-83 1978-83 1980-83 1977-83 1980-83 1980-83 1981-83 1981-83 1980-83 1978-83 1982 1976-83 1978-83 1981-84 1983-84 1981-83 1982-83 1983-84 1982-83 1978-81 1983-84 1983-84 1982-84 1982-83 1983-84 1982-84
Har., 1984 Har., 1984 Har., 1984 Mar., 1984 Har., 1984 Har., 1984 Har., 1984 Har., 1984 Har., 1984 Apr., 1984 Apr., 1984 Hov., 1984 Apr., 1984 Nov., 1984 Nov., 1984 Apr., 1984 Hay, 1984 Hay, 1984 Hay, 1984 Jan., 1985 Jan., 1985 Jan., 1985 Feb., 1985 Feb., 1985 Hay, 1985 Hay, 1985
Application rates of 2 lb. Al/acre to soil except for Soil no. 12 (1.5 lb/A), Soil no. 15 (foliar 0.75 lb./A.) and Soil no. 22 (1 lb./A).
P! S!
o a a
H
o O
a w o
436
GETZIN AND SHANKS
MATERIALS AND METHODS Carbofuran persistence was measured in soils collected from 26 locations in 1984 and early 1985 (Table 1). Two soil samples were taken at each location. The "treated" sample was collected from a field with a documented history of carbofuran
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use. A second sample, the non-treated "control" was collected from an adjacent or nearby field that had no known history of carbofuran use. Most of the fields with a history of carbofuran use had established plantings of strawberries, raspberries, cranberries, or mint. The number of previous carbofuran treatments ranged from 1 to 14, A composite sample consisting of nine cores (10 cm deep x 10.4 cm diam.) was taken from each treated field with a cylindrical soil sampler. A composite of five cores was taken from the adjacent control site. Precautions were taken to minimize cross-contamination of soil samples. Control areas were always sampled first at each location and the sampling tool was washed free of soil and then soaked in a solution of either sodium hypochlorite or a commercial antiseptic agent (0-SYL, National Laboratories, Montvale, New Jersey) between locations. Composite samples were transported to the laboratory, partially dried to a workable condition when necessary, screened through a 3.2-mm mesh sieve, blended, and stored in double 1.25-mil plastic bags at 5°C. All sieving equipment was washed and soaked in a solution of the commercial antiseptic agent between samples. Table 1 gives the source, location, cropping system, and carbofuran use history of the treated fields. Soil moisture equivalents were determined by the method of Briggs and McLane (1907). Organic matter was measured by the method of Walkley and Black (1934). Soil pH was determined by mixing 10 g of dry soil with 20 ml of distilled water, and measuring pH after 30 minutes with a pH meter. A mechanical analysis
ENHANCED DEGRADATION OF CARBOFURAN
437
of each soil was conducted by methods of Boyoucos (1936) after organic matter _ was digested with hydrogen peroxide. The properties of each soil are shown in Table 2. 14 C-carbonyl carbofuran (14.36 mCi/mM) was provided by FMC
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Corporation, Princeton, NJ. On receipt, the product was partitioned between water and chloroform to a radiochemical purity of 98%. Reference standards of nonradioactive carbofuran, 3-hydroxy carbofuran and 3-keto-carbofuran, and a commercial flowable concentrate formulation of carbofuran (Furadan 4F) also were obtained from FMC Corporation. Scintillation cocktail was prepared by dissolving 23 g of premixed scintillators (OMNIFLUOR, New England Nuclear, Boston, MA) in 4 liters of toluene. Ten ml of water containing iu,Ci of
C-carbofuran and 4 mg of non-
radioactive insecticide (Furadan 4F) were sprayed with DeViibis atomizer onto 400 cc of moist soil in an open faced 3.8-liter rotating blender. Additional water was applied to bring the water content of the soil to its soil moisture equivalent (Briggs and McLane 1907). Persistence of
14
C-carbofuran was measured in soils that were mixed at
intervals during the post-treatment incubation period, in soils that were incubated without mixing, and in soil samples from a few treated fields that were autoclaved to destroy microorganisms. To kill microorganisms, 400-cc volumes of moist soil were autoclaved at 15 psi for 1 hr. Autoclaved soil was sterile initially, but became contaminated with airborne spores during application of
14
C-carbofuran and
subsequent handling procedures. To determine persistence of carbofuran in soil that was not mixed during post-treatment incubation, 20-cc volumes of treated soil were weighed Into 60-cc glass bottles. The bottles were stoppered with plastic foam
438
GETZIN AND SHANKS
TABLE 2 Some Chemical and Physical Properties of Soils Used in This Study. Soil Mechanical analysis b _ c d PH no. SME O.M. C.E.C. % sand % silt % clay
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3C 3T 4C 4T 5C 5T 6C 6T 7C 7T 8C 8T 9C 9T 10C 10T 11C 11T 12C 12T 13C 13T 14C 14T 15C 15T 16C 16T 17C 17T 18C 18T 19C 19T 20C 20T 21C 21T 22C 22T
23C 23T 24C 24T 25C 25T 26C 26T 27C 27T 28C 28T
31 30 31 26 34 34 25 22 23 23 24 24 28 26 29 25 28 28 150 85 42 39 20 18 22 18 32 28 26
24 26 33 31 30 34 34 25 26 28 18 22 27 29 35 39 37 34 35 32 30 22 30
4.9 5.2 4.9 5.1 4.8 4.8 4.9 5.3 6.7 5.3 6.0 4.7 6.2 5.9 6.7 6.1 6.0 5.4 5.2 5.2 6.0 6.1 5.9 6.1 7.4 7.4 5.3 5.3 6.0 5.1 6.0 6.5 5.9 6.0 5.8 5.9 6.3 6.2 7.9 6.6 5.4 5.6 5.3 5.9 5.6 5.9 6.1 5.4 5.8 4.7 5.6
6.0
5.1 3.7 5.1 2.0 1.9 5.0 7.6 1.5 2.0 2.0 3.3 3.2 4.6 3.3 3.9 2.7 5.5 4.0
56.8 45.0 8.7 6.4 3.0 1.1 2.3 1.1 7.9 6.3 3.1 3.1 2.9 1.6 3.9 3.5 4.0 3.9 3.1 3.3 5.3 2.1 1.6 2.5 2.3 3.2 6.0 5.8 5.0 4.4 5.0 5.5 4.2 5.2
18.5 16.7 18.5 7.4 7.3
18.0 18.2 8.8
13.5 14.5 19.2 19.0 18.2 14.0 32.0 27.5 22.0 16.5 107.5 72.5 33.7 27.5 16.0 16.0 12.5 18.5 33.3 29.5 20.0 20.5 12.8 16.8 19.5 17.5 20.0 25.0 12.5 13.3 36.8 20.0 9.3
13.5 12.5 16.5 21.0 22.0 18.0 17.0 21.2 20.4 13.9 20.8
97 98 97 98 98 97 92 97 25 21 21 23 19 19 19 25 13 13 . .
9 12 64 67 41 58 44 41 42 45 49 41 56 60 49 49 59 62 32 49 66 57 24 13 10 17 27 17 49 52 68 51
3 2 3 2 2 3 7 3 55 58 52 53 59 60 64 41 56 62 . 44 44 74 21 42 31 38 41 37 36 40 42 32 29 40 41 28 26 42 28 29 36 57 64 57 51 55 57 33 33 22 38
0 0 0 0 0 0 . 1 0 20 21 27 24 22 21 17 34 31 25 . 47 44 12 12 17 11 1B 18 21 19 11 17 12 11 11 10 13 12 26 23 5 7 19 23 33 32 18 26 18 15 10 11
Soil
sand sand sand sand sand sand sand sand silt loam silt loam silt loam silt loam silt loam silt loam silt loam clay loam silty clay loam silt loam organic organic silty clay silty clay sandy loam sandy loam loam sandy loam loam loam loam loam loam loam sandy loam sandy loam loam loam sandy loam sandy loam loam sandy clay loam sandy loam sandy loam silt loam silt loam silty clay loam silty clay loam silt loam silt loam loam loam sandy loam loam
T = site with previous carbofuran use history; C = control site with no history of carbofuran use Soil moisture equivalent. j Organic matter; ; Cation exchange capacity (meq/100 g of soil);
b
ENHANCED DEGRADATION OF CARBOFURAN
A39
culture tube plugs, placed on trays in 1.25-mil plastic bags containing a small amount of water to maintain a water vapor saturated atmosphere, and incubated undisturbed. To determine persistence of carbofuran in soil that was mixed during laboratory incubation, each 400-cc volume of treated soil was placed in a double
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1.25-mil plastic bag. The soil was blended in the bag for ca 30 sec each time a subsample was removed for analysis. All treated samples of soil were incubated in the dark at 20 ± 1 °C. Most soil treatments were duplicated, some were replicated 4 times. Immediately after treatment and at selected intervals thereafter, samples of each treated soil were analyzed for
14 C-carbofuran. Sampling was conducted at 1-4
day intervals, depending upon rapidity of degradation, for the first week, weekly until after 4 weeks, and biweekly until 16 weeks had elapsed. For non-mixed samples, the soil from each bottle was transferred to a 250-ml polyethylene centrifuge bottle with 100 ml of extracting solvent (90% acetone and 10% 0.25N HC1). For soils that were bulk-stored in plastic bags for mixing during the incubation period, a 20-cc volume of soil was weighed out from the plastic bag with a disposable plastic spoon and placed in a 250-ml polyethylene bottle with 100 ml of solvent. The bottles were stoppered, agitated on a reciprocating shaker for 45 min and then centrifuged at 1000 x g for 10 min. Five ml of supernatant were transferred to a 25-ml screw cap centrifuge tube. The solvent was evaporated to near dryness, and the residue was partitioned between 5-ml volumes of methylene chloride and water to separate
14 C-
carbofuran from small amounts of water soluble radioactivity in the acetone:water extract. After centrifuging at 1000 x g for 5 min, 2 ml of the methylene chloride layer were transferred to a glass scintillation vial, the solvent was evaporated, and the residue was dissolved in 8 ml of scintillation cocktail. Radioactivity was counted in a TM Analytic Model 6895 Automatic Liquid Scintillation System.
440
GETZIN AND SHANKS
Radioactivity in methylene chloride from selected samples also was separated with thin-layer chromatography using etherhexane (3:1) as the developing solvent (Getzin 1973) to determine if radioactive components other than carbofuran were present.
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RESULTS Texture of the soils used varied from almost pure sands containing some organic matter (cranberry sites) to silty clay loams containing over 30% clay (Table 2). An organic soil (Soil 12) also was included. Soil acidity generally ranged from pH 5 to pH 6.5 although three soils (15C, 15T and 22C) were above pH 7.0. Soil pH readings shown in Table 2 were taken at the beginning of an experiment. Usually soil pH declined 0.2 to 0.4 units during the course of the incubation period. Organic matter content generally ranged from 2-6% with the exception of Soil 12 which contained approximately 50% organic matter. Moisture contents of treated soils decreased only slightly during the course of the experiments. Adjustments were made in weights of samples removed for extraction from bulk volumes of test soils (mixed treatments) to compensate for the slight loss of water. Recoveries of total radioactivity from soil averaged 101 ± 3 % when soil was fortified with known amounts of
C-carbofuran. Extracted
C was converted to
percentage of carbofuran recovered. Initial recovery of carbofuran from all soils was 97 ± 2%. Previous studies with other insecticides indicated that about 5% loss of insecticide occurred while the chemical is being sprayed on the soil. Thin-layer chromatographic separation of solvent-partitioned extracts from selected soil samples gave a single major compound. Exceptions occurred when recovery radioactivity declined to < 5% of the original application. Radioactivity that did not correspond to the R, of authentic carbofuran was present either as a spot at the origin, or as a diffuse streak between the origin and the parent compound. This
ENHANCED DEGRADATION OF CARBOFURAN
441
limited chromatographic survey indicated that the extraction, solvent partition, and radioassay procedures employed were satisfactory for monitoring persistence of parent carbofuran in soils. Carbofuran persistence was expressed as a pseudo half-life, i.e., the time for
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50% loss of the parent compound, (Table 3) determined by 'best fit' observations (Hamaker 1972). Because of the shape of the persistence curves and the limited number of data points during critical insecticide decay intervals for some soils, mathematical treatment of the data did not give meaningful results. Carbofuran persistence varied greatly between soils. For 22 of the 26 locations, the insecticide degraded faster in samples from previously-treated fields than in samples from paired control sites that had no history of carbofuran use whether the samples were mixed or not. Exceptions were Soils 8, 11, 15, and 27 where similar degradation rates were observed for previously-treated fields and the paired controls in mixed and/or non-mixed soils. Large differences in decay rates were also observed between soils from the fields with a history of previous carbofuran use. The time for 50% loss of insecticide in previously treated fields ranged from 2.5 days to > 70 days. Pseudo half-lives of 9 days or less were recorded for samples from 15 of the 26 sites surveyed. Substantial variation of decay rates also was found in samples from fields that had no history of previous carbofuran use. Pseudo half-lives of 15 to 28 days were found in samples from 15 controls fields. In 9 mixed control soils and in 21 nonmixed control soils the pseudo half-life exceeded 70 days. The shortest pseudo-life of carbofuran in mixed control soil was 12 days (Soil 19). The shortest pseudo halflife for non-mixed control soils was 23 days (Soils 19 and 23). Initial lag phases of three days or more preceded rapid decline rates in a large number of soils from both treated and non-treated fields. Seldom did the insecticide decline curves exhibit classic 1st-order rate behavior. Lag patterns are
442
GETZIN AND SHANKS
TABLE 3 a
Pseudo Half-lives of
14
C-carbofuran in Soils With and Without a Carbofuran-Use History. Pseudo half-life of carbofuran (days)
Mixed soil
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Soil
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
C
T
28 28*
40 21* 22*
8* 6 12* 34 6.5 6.5 4
(70)
7.5*
27*
30*
(53) (81)
25.5* (64) 16 74
(68) 89* 19* 12*
(59) 19* 19* 15* 25*
(63) (61) 18* 19*
11.5* 25* 2.5 18* 4 20 8* 4 7* 9* 7*
6.5* 6.5* 4 32* 16 4
b
Non-mixed soil A
C
T
73 73
9.5*
(90)
(94) (82) (61)
70
(87)
100
102
9.5*
(62)
63 2.5 72 3 70 8* 4 8*
35 70
(62) (75)
e*
70
(62) (56)
40
(63) (92)
(90)
6.5 19* 37 6.5 4
(51) (73) (88)
A
91 112 23*
(54) (56*)I
(94) (87) (65) (86) (79)
10.5*
(79) (87)
36* 23*
(83)
3.5
5.5* 5.5* (70)
(56)
73
72 91
19.5
(65)
(82)
6*
(85) (88) (87)
4
14 Pseudo half-life is the time for 50% loss of C-carbofuran in soil incubated at 20° C. Numbers in parentheses indicate percentage of original carbofuran remaining when study was terminated at 112 days (pseudo half-life was > 112 days). Asterisks indicate carbofuran degradation was preceded by an initial lag phase of 3 days or more: T = soil from field previously treated with carbofuran; A = autoclaved soil from treated site; C = soil from non-treated control site.
characteristic of the induction of microbiai populations with a capacity to degrade the insecticide (Alexander 1981). Carbofuran persistence in autoclaved soil was measured to determine rates of nonmicrobial degradation, and to monitor the extent of cross-contamination that occurred during insecticide treatment in the laboratory and subsequent handling
ENHANCED DEGRADATION OF CARBOFURAN
443
procedures. Although precautions were taken to prevent it, some crosscontamination did occur for treatments where the soil was bulk stored in plastic bags and mixed frequently during the incubation period. Cross-contamination was indicated when the decline curves for individual replicates of a treatment greatly
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differed. An example of where contamination probably occurred in both replicates of an autoclaved treatment is Soil 19A, which had a pseudo half-life of only 70 days compared to over 112 days for all other autoclaved samples. Because no contamination appeared in non-mixed treatment tests, it is possible that contamination occurred during the frequent handling of the bulk soil samples after the soil was treated with radio-labeled carbofuran. Contamination also appeared in single replicates of several mixed control soils. Differences in the decline curve between replications occurred after the 8-week sampling period for control Soils 5, 25, and 26. When the decline curves for both replicates of a treatment exhibited an extended lag phase followed by a rapid decline of insecticide, the experiment was repeated. Carbofuran was highly persistent in most autoclaved soils. The time for 50% loss of insecticide exceeded 112 days in all instances except for the mixed treatment in Soil 19. Excluding Soil 19A, the amount of the insecticide remaining in autoclaved soil samples at 112 days ranged from 61 to 94% of the original application dosage. The fastest breakdown occurred in autoclaved samples of Soil 15, which was the soil with the highest pH.
DISCUSSION The finding that carbofuran usually degraded much faster in soil samples taken from fields with a history of carbofuran use than in soil samples taken from adjacent fields with no history of carbofuran use suggests that enhanced
444
GETZIN AND SHANKS
degradation occurs in the Pacific Northwest. Enhanced degradation developed with as few as one or two applications of carbofuran, which was also observed by Harris et al. (1984, 1988). In the laboratory tests, accelerated degradation developed during the course of an initial treatment in some soil samples not previously exposed
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to carbofuran treatment. Similar observations have been made by Harris et al. (1988) and Dzantor and Felsot (1989). Since frequent blending of treated soil accelerated degradation in some laboratory samples, cultivation and other mechanical disturbances alone may enhance the rate of degradation. Harris et al. (1984) observed significantly faster degradation in soils that were mixed than in soils that were unmixed and they concluded that mixing efficiently distributed active microorganisms throughout the soil. Soils from fields with a natural pH lower than 5.8 did not show evidence of rapid microbial degradation of carbofuran in studies by Read (1986). Walker et al. (1986) observed slow degradation of the fungicides iprodione and vinclozolin in soil with a pH of 5.0 and suggested that the microorganisms responsible for degradation of the chemicals was inhibited by the low pH. In our studies, soils with a pH less than 5.0, e.g. Soils 3-5 and 27, showed definite enhanced degradation of carbofuran after the fields had been treated with that chemical. The slow decay rate of carbofuran in autoclaved soil suggests that the insecticide will persist for long periods in subsurface soil zones with low microbial activity. This may influence the potential for ground water contamination in areas with rainfall, coarse-textured soils and shallow water tables. In conclusion rapid loss of carbofuran in some soils suggests that enhanced i
degradation may account for the poor insect control that has been reported for several locations in the Pacific Northwest. Field studies that combine efficacy tests with insecticide residue tests are needed to determine if enhanced degradation is actually responsible for these insect control failures.
ENHANCED DEGRADATION OF CARBOFURAN
445
ACKNOWLEDGMENTS The assistance of Darrell Barstow in the conduct of this research is gratefully acknowledged. Thanks are due also to A. S. Felsot and C. R. Harris for their critical reviews of the manuscript. Research was conducted under Projects 0741 and 1957,
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Washington State. University, College of Agriculture and Home Economics, Research Center, Pullman, Wash. 99164.
REFERENCES CITED Alexander, M., Science 211, 132-138 (1981). Bouyoucos, G.J., Soil Sci. 42, 225-229 (1936). Briggs, L.J. and McLane, J.W., USDA Soils Bureau Bull. 45 (1907). Dzantor, E.K. and Felsot, A.S., J. Environ. Sci. Hlth. B24, 569-587 (1989). Felsot, A.S., Annu. Rev. Entomol. 34, 453-476 (1989). Felsot, A., Maddox, J.V., and Bruce, W., Bull. Environ. Contam. Toxicol. 26, 781788 (1981). Felsot, A.S., Steffey, K.L., Levine, E., and Wilson, J.G., J. Econ. Entomol. 78, 45-52 (1985). Felsot, A.S., Wilson, J.G., Kuhlman, D.E. and Steffey, K.L., J. Econ. Entomol. 75, 1098-1103 (1982). Getzln, L.W., Environ. Entomol. 2, 461-467 (1973).
Hamaker, J.W. IN Organic Chemicals in the Soil Environment, Vol. I. C. A. I. Goring and J.W. Hamaker [eds.], Marcel Dekker, New York, pp. 253-340 (1972). Harris, C.R., Chapman, R.A., Harris, C., and Tu, C.M., J. Environ. Sci. Hlth. B19, 111 (1984). Harris, C.R., Chapman, R.A., Morris, R.F., and Stevenson, A.B., J. Environ. Sci. Hlth. B23. 301-316 (1988). Harris, C.R., Chapman, R.A., Tolman, J.H., Moy, P., Henning, K., and Harris, C , J. Environ. Sci.. Hlth B22, 1-32 (1988).
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Kauffman, D.D. and Edwards, D.F. IN Pesticide Chemistry:Human Welfare and the Environment. J. Miyamoto & P. C. Kearny [eds.], Pergamon, Oxford, UK, pp. 173-182 (1983). Suett, D.L., Crop Protection g: 371-378 (1987).
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Walkey, A. and Black, I.A., Soil Sci. 27, 29-38 (1934).
Received: April 10, 1990
