© 2000 CRC Press LLC chapter ten Other pesticides 10.1Chapter overview The pesticide active ingredients covered in this chapter represent a wide array of compounds that do not lend themselves to easy classification. They are therefore organized according to their use; that is, fungicides, herbicides, insecticides, and others. 10.2Fungicides 10.2.1Benomyl Trade or other names Commercial names for products containing benomyl include Agrocit, Benex, Benlate, Benosan, Fundazol, Fungidice 1991, and Tersan 1991. Benomyl is compatible with many other pesticides. Regulatory status Benomyl is a General Use Pesticide (GUP). The EPA categorizes it as toxicity class IV — practically nontoxic. Benomyl-containing products carry the Signal Word CAUTION. Introduction Benomyl is a systemic, benzimidazole fungicide that is selectively toxic to micro- organisms and to invertebrates, especially earthworms. It is used against a wide range of fungal diseases of field crops, fruits, nuts, ornamentals, mushrooms, and Figure 10.1 Benomyl. L1190 CH10 pgs Page 411 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC turf. Formulations include wettable powder, dry flowable powder, and dispersible granules. Toxicological effects Acute toxicity Benomyl is of such a low acute toxicity to mammals that it has been impossible or impractical to administer doses large enough to firmly establish an LD 50 . Thus, the LD 50 is greater than 10,000 mg/kg in rats and greater than 3400 mg/kg in rabbits (using a 50% wettable powder formulation). Because of its high LD 50 , there is a low risk for acute poisoning from this compound (1). Skin irritation may occur for workers exposed to benomyl. Skin reactions have also been seen in rats and guinea pigs. Most organisms can become sensitized to the compound as well. Benomyl is readily absorbed into the body by inhaling the dust, but there are no reports of toxic effects to humans by this route of exposure. The inhalation LC 50 in rats is greater than 2 mg/L (2). Chronic toxicity When rats were fed diets containing about 150 mg/kg/day for 2 years, no toxic effects were observed (3). Dogs fed benomyl in their diets for 3 months had no major toxic effects, but did show evidence of altered liver function at the highest dose (150 mg/kg). The damage progressed to more severely impaired liver function and liver cirrhosis after 2 years (6). Reproductive effects A three-generation study on rats showed no reproductive or lactational differ- ences at a dose of 150 mg/kg/day administered in the diet (3). In another study in rats, the testes were the most affected sites at relatively low doses of about 15 mg/kg/day. Male rats had decreased sperm counts, decreased testicular weight, and lower fertility rates. The animals recovered from these effects 70 days after feeding with the pesticide had stopped (3). Reproductive effects in humans are unlikely at expected exposure levels. Teratogenic effects Very high doses of benomyl can cause birth defects in test animals (4). Rats fed 150 mg/kg/day in the diet for three generations showed no birth defects. No ter- atogenicity was observed in another study of rats given 300 mg/kg/day on days 6 to 15 of gestation (4). At higher doses, some birth defects were noted, but they were accompanied by toxicity to the fetus (4). In another rat study where mothers were fed 1000 mg/kg/day for 4 months, the offspring showed a decrease in viability and fertility (1). These data suggest that benomyl is not likely to cause teratogenic effects under normal circumstances. Mutagenic effects Conflicting negative and positive results have been found in numerous mutage- nicity assays. As a result, no conclusions about the mutagenicity of benomyl can be drawn (3). L1190 CH10 pgs Page 412 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC Carcinogenic effects Tumors in the livers of both male and female mice were observed in lifetime studies at doses of benomyl at 40 to 400 mg/kg/day. In a 2-year dietary study when albino rats were fed up to 2500 mg/kg/day benomyl, there were no significant adverse effects at any dose level attributable to benomyl (1). Based on these data, it is not possible to determine the carcinogenicity of benomyl (5). Organ toxicity Target organs identified in animal studies included the liver and testes. Fate in humans and animals Benomyl’s metabolism has been studied in the mouse, rat, rabbit, dog, sheep, and cow. Benomyl is rapidly broken down to carbendazim, and further to other compounds such as 5-hydroxy-2-benzimidazole carbamate (5-HBC), and then elim- inated. In a rat study, benomyl, carbendazim (MBC), and 5-HBC were found in rat blood in the first 6 hours. After 18 hours, only 5-HBC was present. The urine con- tained about 40 to 70% of the dose, and the feces 20 to 45%. No residues were found in muscle or fat. Benomyl and its metabolites do not accumulate in tissues over long- term exposure periods (2,3). Carbendazim (MBC) and the parent compound benomyl have similar toxicological properties, but the former is not a skin sensitizer (2). Ecological effects Effects on birds In bobwhite quail and mallard ducks, the 5-day dietary LC 50 for benomyl is greater than 10,000 ppm. In redwing blackbirds, the LD 50 value is 100 mg/kg, which indicates that benomyl is moderately toxic to this species (4). Effects on aquatic organisms Benomyl is highly to very highly toxic to fish. The order of susceptibility to benomyl for various fish species from least susceptible to most susceptible is: catfish, bluegill, rainbow trout, and goldfish. The LC 50 values for the compound in fish are 0.05 to 14 mg/L in adults, and 0.006 mg/L in catfish fry (8). The main breakdown product, carbendazim, had the same order of toxicity as benomyl. Crayfish have an LC 50 greater than 100 mg/L. The estimated bioconcentration factor (BCF) ranges from 159 in rainbow trout up to 460 in bluegill sunfish, indicating that benomyl does not tend to significantly concentrate in living tissue (8,9). Effects on other organisms (non-target species) A single application of benomyl to turfgrass can substantially reduce some soil-dwelling organisms. The compound is very lethal to earthworms at low con- centrations over a long time period. The 7-day LC 50 in earthworms is 1.7 mg/L, and the 14-day LC 50 is 0.4 mg/L (6). Benomyl also decreases the mixing of soil and thatch. The effects last for up to 20 weeks (10). Benomyl is relatively nontoxic to bees (2). L1190 CH10 pgs Page 413 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC Environmental fate Breakdown in soil and groundwater Benomyl is strongly bound to soil and does not dissolve in water in flooded rice fields to any significant extent (2,11). It is highly persistent. When applied to turf, it has a half-life of 3 to 6 months and, when applied to bare soil, the half-life is 6 to 12 months. Where four successive annual applications were applied, residues did not accumulate from one year to the next (6). Breakdown in water Benomyl completely degrades to carbendazim within several hours in acidic or neutral water. The half-life of carbendazim is 2 months (1). Breakdown in vegetation Since benomyl is a systemic fungicide, it is absorbed by plants. Once it is in the plant, it accumulates in veins and at the leaf margins (6). The metabolite carbendazim seems to be the fungicidally active agent. Benomyl residues are quite stable, with 48 to 97% remaining as the parent compound 21 to 23 days after application (6). Physical properties Benomyl is a tan crystalline solid compound. It has little or no odor (1). Chemical name: methyl 1-[(butylamino)carbonyl]-H-benzimidazol-2-ylcarbam- ate (1) CAS #: 17804-35-2 Molecular weight: 290.62 (1) Solubility in water: 2 mg/L (1) Solubility in other solvents: chloroform s.; heptane s.; ethanol s.; acetone s. (1) Melting point: Decomposes without melting above 300 ° C (1) Vapor pressure: Negligible (<1 mPa) at 20 ° C (1) Partition coefficient (octanol/water): Not available Adsorption coefficient: 1900 (11) Exposure guidelines ADI: 0.02 mg/kg/day (12) HA: Not available RfD: 0.05 mg/kg/day (13) PEL: 5 mg/m 3 (8-hour) (respirable fraction) (14) Basic manufacturer DuPont Agricultural Products Walker’s Mill, Barley Mill Plaza P.O. Box 80038 Wilmington, DE 19880-0038 Telephone:800-441-7515 Emergency:800-441-3637 L1190 CH10 pgs Page 414 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC 10.2.2Captan Trade or other names Trade names for captan include Agrox, Captal, Captec, Captol, Captonex, Clo- mitane, Merpan, Meteoro, Orthocide, Phytocape, Sepicap, Sorene, and Vancide 89. Captan may be found in formulations with a wide range of other pesticides. Regulatory status Captan is a General Use Pesticide (GUP), though most uses of the compound on food crops were canceled in the U.S. in 1989. It is categorized as toxicity class IV — practically nontoxic. However, it bears the Signal Words DANGER or CAU- TION if packaged in concentrated form because it can be irritating to the skin and eyes. Introduction Captan is a nonsystemic phthalimide fungicide used to control diseases of many fruit, ornamental, and vegetable crops. It improves fruit finish by giving it a healthy, bright-colored appearance. It is used in agricultural production as well as by the home gardener. A major use of captan is in apple production. Toxicological effects Acute toxicity The rat oral LD 50 for captan ranges from 8400 to 15,000 mg/kg, indicating very low acute toxicity (15). The mouse LD 50 is 7000 mg/kg. Sheep showed no effect at doses of 200 mg/kg, but experienced deaths at 250 mg/kg. The inhalation LC 50 (2- hour) in mice is 5.0 mg/L (8). Rabbits showed little or no skin sensitization to captan, while guinea pigs were moderately sensitive (6). Workers exposed to high concentrations of captan in air (6 mg/m 3 ) experienced eye irritation, including burning, itching, and tearing. Skin irritation also occurred in some cases (6). Chronic toxicity Rats fed up to 750 mg/kg/day Orthocide for 4 weeks had decreased food intake and body weights (6). No deaths occurred in pigs given as much as 420 to 4000 mg/kg/day in the diet for 12 to 25 weeks; however cattle given six doses of 250 mg/kg experienced varied toxic effects, including death (6). Figure 10.2 Captan. L1190 CH10 pgs Page 415 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC Reproductive effects Pregnant mice exposed by inhalation to high doses of captan for 4 hours a day during days 6 to 15 of gestation showed significant mortality or weight loss. Fetal mortality accompanied these effects. Mice fed 50 mg/kg/day over three generations reproduced normally. Captan is unlikely to cause reproductive effects in humans at usual levels of exposure (6,8). Teratogenic effects Teratogenicity studies with rats, rabbits, hamsters, and dogs have given both negative and positive results. However, the weight of evidence suggests that captan does not produce birth defects (16). Mutagenic effects Although captan was mutagenic in some laboratory tests on isolated tissue cultures, the majority of evidence indicates that captan is nonmutagenic (16). Carcinogenic effects There is strong evidence that captan causes cancer in female mice and male rats at high doses. In addition, captan is chemically similar to two other pesticides, folpet and captafol, that have been shown to produce cancer in test animals. Tumors were associated with the gastrointestinal tract and, to a lesser degree, with the kidneys. Tumors appeared in the test animals at doses of about 300 mg/kg/day (6,8). Organ toxicity Most organ-specific effects are found in the kidneys of rats at and above doses of 100 mg/kg/day. Fate in humans and animals Studies in several animal species have shown that captan is rapidly absorbed from the gastrointestinal tract and is rapidly metabolized. Residues are excreted primarily in the urine. Rats given captan orally excreted a third in the feces and half in the urine within 24 hours. A cow fed small amounts in its diet for 4 days had no captan in the milk at a 0.01-mg/L detection limit, nor could any be detected in the urine at a 0.1-mg/L detection limit (6). Ecological effects Effects in birds Captan is practically nontoxic to birds. The LD 50 is greater than 5000 mg/kg in mallard ducks and pheasants. The LD 50 is 2000 to 4000 mg/kg in bobwhite quail (1). High doses administered for 90 days to chickens caused an 80% reduction in the number of eggs produced but had no effect on the fertility or hatchability of the eggs produced (6). Effects in aquatic organisms Captan is very highly toxic to fish. The LC 50 (96-hour) for technical captan ranges from 0.056 mg/L in cutthroat trout and chinook salmon to 0.072 mg/L in bluegill (1). L1190 CH10 pgs Page 416 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC The LC 50 for captan in the aquatic invertebrate Daphnia magna is 7 to 10 mg/L, indicating that the compound is moderately toxic to this and other aquatic inverte- brates (8). Captan has a low to moderate tendency to accumulate in living tissue. Fish exposed for 3 days to concentrations that would be expected in a pond following treatment of an adjacent watershed at a rate of 1 lb/acre, had no detectable residues of captan (6). Estimates of the bioconcentration factor range from 10 to 1000 (9). Effects on other organisms (non-target species) Captan is not toxic to bees when used as directed (1). Environmental fate Breakdown in soil and groundwater Captan has a low persistence in soil, with a half-life of 1 to 10 days in most soil environments (6). Captan was not detected in field studies of its mobility at appli- cation rates of up to 42 kg active ingredient per hectare (9). Breakdown in water Captan is rapidly degraded in near neutral water. Half-lives of 23 to 54 hours and 1 to 7 hours have been reported at various acidities and temperatures (6). The effective residual life in water is 2 weeks (15). Breakdown in vegetation Captan is taken up through leaves and roots and translocated throughout the plant. Residual fungitoxicity remains for 23 days after application on potato leaves, but residues were below the detection limit within 40 days after application (6). Some varieties of apples, pears, lettuce seeds, celery, and tomato seeds may be injured by captan at high doses (1). Physical properties Captan is a white to buff-colored compound in the technical form. It is a colorless crystal in its pure form (1). The technical product has a pungent smell. Chemical name: 3a,4,7,7a-tetrahydro-2-[(trichloromethyl)thio]-1H-isoindole- 1,3(2H)-dione (1) CAS #: 133-06-2 Molecular weight: 300.61 (1) Solubility in water: 3.3 mg/L @ 25 ° C (1) Solubility in other solvents: xylene s.; acetone s.; chloroform v.s.; cyclohexanone v.s. (1) Melting point: 178 ° C (1) Vapor pressure: 1.3 mPa @ 25 ° C (1) Partition coefficient (octanol/water): 610 (1) Adsorption coefficient: 200 (11) L1190 CH10 pgs Page 417 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC Exposure guidelines ADI: 0.1 mg/kg/day (12) MCL: Not available RfD: 0.13 mg/kg/day (13) TLV: 5 mg/m 3 (8-hour) (17) Basic manufacturer Drexel Chemical Company 1700 Channel Avenue Memphis, TN 38113 Telephone:901-774-4370 10.2.3Carboxin Trade or other names Trade names for products containing carboxin include Cadan, Kisvax, Kemikar, Oxalin, Padan, Sanvex, Thiobel, Vegetox, and Vitavax. It is often used in combination with other fungicides such as thiram or captan. Regulatory status Carboxin is classified as a General Use Pesticide (GUP) by the U.S. Environmental Protection Agency. It is in toxicity class III — slightly toxic, and products containing it carry the Signal Word CAUTION on the label. Introduction Carboxin is a systemic anilide fungicide. It is used as a seed treatment for control of smut, rot, and blight on barley, oats, rice, cotton, vegetables, corn, and wheat. It is also used to control fairy rings on turfgrass. Carboxin may be used to prevent the formation of these diseases or may be used to cure existing plant diseases. Toxicological effects Acute toxicity Carboxin is slightly toxic. Symptoms of poisoning can include vomiting and headache. Recovery is very rapid if the exposed individual is treated quickly. The oral LD 50 is 3820 mg/kg in rats and 3550 mg/kg in mice (18). Figure 10.3 Carboxin. L1190 CH10 pgs Page 418 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC The compound produces very little skin irritation; however, it can seriously irritate the eyes. Acute dermal exposure results in an LD 50 of greater than 8000 mg/kg in rabbits. The inhalation LC 50 (1-hour) is greater than 20 mg/L in rats (18). Chronic toxicity Rats fed doses up to 311 mg/kg/day for 28 days showed some fluid accumula- tion in the liver, even at low doses (18). Another rat study showed kidney changes at somewhat higher doses (1000 mg/kg fed for 90 days) (18). A 2-year rat study with levels of up to 30 mg/kg produced no compound-related effects in physical appear- ance, behavior, blood chemistry, or urinalysis (18). However, there were changes in organ weights. Male and female mice also showed liver effects after being fed high doses (912 mg/kg) of carboxin for 1 1 / 2 years (18). Beagle dogs showed no effects at the highest dose tested, 15 mg/kg for two years (18). Reproductive effects A three-generation study with rats showed treatment-related effects on repro- ductive performance at levels from 5 to 30 mg/kg/day. However, at the highest dose, there was only moderate growth suppression in nursing pups (18). It is unlikely that the compound would produce reproductive effects in humans at expected expo- sure levels. Teratogenic effects At the highest dose tested (40 mg/kg), administered to pregnant rats on days 6 to 15, there were no birth defects in the offspring (18). Pregnant rabbits treated with very high doses on days 6 to 27 of gestation had increased abortions but no fetal malformations (18). These data indicate that carboxin is not teratogenic. Mutagenic effects Carboxin is either a non-mutagen or is a very weak mutagen, based on infor- mation from several studies on bacteria and mammalian cells (18). Carcinogenic effects A 2-year study with rats fed up to 30 mg/kg/day showed no evidence of increased tumor frequency (18). Mice fed up to 900 mg/kg/day for 84 weeks had no apparent compound-related increase in tumor formation. Carboxin does not appear to cause cancer. Organ toxicity Animal studies have demonstrated effects in the liver and the kidneys. Fate in humans and animals Rats excreted almost all of a carboxin dose in 24 hours, with most excreted in urine and some in feces (15). Rabbits showed a similar excretion pattern. Carboxin is incompletely absorbed in the gut, especially in rats (18). The compound does not acumulate in animal tissues. Only trace amounts of carboxin were found in rat tissues 48 hours after dosing (18). In milk cows fed up to 5 ppm for 10 days, less than 2% of the administered L1190 CH10 pgs Page 419 Friday, July 2, 1999 5:31 PM © 2000 CRC Press LLC dose was found in tissues. However, significant levels were found in milk a few days after exposure. The main breakdown product is carboxin sulfoxide for which the rat oral LD 50 is 2000 mg/kg. Carboxin sulfoxide is sold as a pesticide also and is known as oxycarboxin (19). Ecological effects Effects on birds The oral LD 50 of carboxin in chickens is very high, at 24 g/kg, indicating that it has a very low acute toxicity (8). In chronic, low-exposure experiments over 5 1 / 2 months, changes were noted in the digestive tract, cardiovascular system, and blood of chickens (20). Effects in aquatic organisms Carboxin is highly toxic to fish. The 96-hour LC 50 in rainbow trout is greater than 0.1 mg/L (8). Carboxin is practically nontoxic to freshwater invertebrates. The LC 50 is 217 mg/L in juvenile crayfish (20). Effects on other organisms (non-target species) The compound is nontoxic to bees (8). Environmental fate Breakdown in soil and groundwater Carboxin is rapidly degraded to carboxin sulfoxide in soil. It has a low persis- tence, with a half-life of about 3 days in soil (11). In one study, after 7 days 95% of the parent was gone and the sulfoxide, a breakdown product, represented 31 to 45% of the amount applied (8). Minor products formed were carboxin sulfone, hydroxy carboxin, and CO 2 . Carboxin does not readily adsorb to soil. Both parent compound and the sulfoxide are very mobile and could possibly leach to groundwater (18). Breakdown in water In water, carboxin oxidizes to the sulfoxide and sulfone within 7 days (18). This happens both under ultraviolet light and in the dark. Blue-green algae (e.g., Anabaena and Nostoc) degrade the pesticide extensively. Other algae can also break down carboxin, but not to the same extent (8). Breakdown in vegetation Although the distribution pattern of the parent and sulfoxide metabolite vary, carboxin is found systemically (throughout the plant) in all species of plants studied. Plants grown from treated seed had no carboxin present at 6 weeks after emergence. Carboxin sulfoxide found in plants can come either from the soil or through oxidation within the plant (8). Physical properties Carboxin is a colorless crystal (1). L1190 CH10 pgs Page 420 Friday, July 2, 1999 5:31 PM [...]...L1190 CH10 pgs Page 421 Friday, July 2, 1999 5:3 1 PM Chemical name: A 5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide (1) CAS #: 523 4-6 8-4 Molecular weight: 235.31 (1) Solubility in water: 170 mg/L @ 25°C (1) Solubility in other solvents: acetone v.s.; benzene s.s.; methanol s.s (1) Melting point: Two crystal structures: 91. 5-9 2.5°C and 9 8-1 00°C (1) Vapor pressure: . (1). L1190 CH10 pgs Page 420 Friday, July 2, 1999 5:3 1 PM © 2000 CRC Press LLC Chemical name: A 5,6-dihydro-2-methyl-N-phenyl-1,4-oxathiin-3-carboxamide (1) CAS #: 523 4-6 8-4 Molecular weight: 235.31. pungent smell. Chemical name: 3a,4,7,7a-tetrahydro- 2-[ (trichloromethyl)thio ]-1 H-isoindole- 1,3(2H)-dione (1) CAS #: 13 3-0 6-2 Molecular weight: 300.61 (1) Solubility in water: 3.3 mg/L @ 25 ° C. (1). Chemical name: methyl 1-[ (butylamino)carbonyl]-H-benzimidazol-2-ylcarbam- ate (1) CAS #: 1780 4-3 5-2 Molecular weight: 290.62 (1) Solubility in water: 2 mg/L (1) Solubility in other solvents: chloroform