Cypermethrin
Total Page：16
File Type：pdf, Size：1020Kb
JOURNAL OF PESTICIDE REFORM/ SUMMER 1996 • VOL.16, NO. 2 ● INSECTICIDE FACTSHEET CYPERMETHRIN Cypermethrin is a synthetic pyrethroid insecticide used to kill insects on cotton and lettuce, and to kill cockroaches, fleas, and termites in houses and other buildings. Cypermethrin is toxic to the nervous system. Symptoms of exposure include dizziness, nausea, headaches, and seizures. It also suppresses the immune system, inhibiting the formation of antibodies to disease-producing microbes. If exposed to cypermethrin during pregnancy, rats give birth to offspring with developmental delays. In male rats exposed to cypermethrin, the proportion of abnormal sperm increases. It causes genetic damage: chromosome abnormalities increased in bone marrow and spleen cells when mice were exposed to cypermethrin. Cypermethrin is classified as a possible human carcinogen becaue it causes an increase in the frequency of lung tumors in female mice. Among structural pest control operators in California, cypermethrin is the fourth most common cause of pesticide-related illness. After household treatments, it persists in the air and on walls and furniture for about three months. Cypermethrin is toxic to bees, other beneficial insects, earthworms. fish, and shrimp. Birds in cypermethrin-treated areas are less successful at raising nestlings because their insect food sources are killed. BY CAROLINE COX insects on cotton.1 In the U.S., use on cot- where pesticide use reporting is more com- ton is important in 5 states.3 (See Figure prehensive than other states, use of 2.) cypermethrin in homes and other buildings Cypermethrin is an insecticide in It is also used on lettuce and pecans, to is the predominant use.4 (See Figure 3.) the synthetic pyrethroid family. It was first kill cockroaches (and other indoor pests) in marketed in 1977.1 The primary manufac- buildings, and to kill termites. In California, Mode of Action turers in the U.S. are Zeneca Inc., FMC Corp., and American Cyanamid Co. Com- mon brand names are Demon, Cymbush, 2 Figure 1 Ammo, and Cynoff. Cypermethrin and Related Naturally-Occurring Insecticidal Chemicals All of the insecticides in this family have chemical structures that are loosely based on pyrethrins, insecticidal compounds O found in chrysanthemum flowers. (See Fig- Cl O ure 1.) Most synthetic pyrethroids are com- Cl O CN plex molecules; cypermethrin is no excep- cypermethrin tion. Because of its complexity, there are (+/-) alpha-cyano-(3-phenoxyphenyl) methyl (+)-cis, eight different ways that the atoms that trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylate make up the cypermethrin molecule can arrange themselves in three dimensions. These are called isomers. Cypermethrin is a O O CH O C mixture of all eight isomers.1 3 2 Over ninety percent of the cypermethrin O O manufactured worldwide is used to kill O O pyrethrin I pyrethrin II Caroline Cox is JPR’s editor. NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP P.O. BOX 1393, EUGENE, OREGON 97440 / (541)344-5044 15 JOURNAL OF PESTICIDE REFORM/ SUMMER 1996 • VOL.16, NO. 2 that kills 50 percent of a population of test Figure 2 Figure 3 animals; LD50) is variable. In rats the LD50 Agricultural Uses of Use of Cypermethrin can vary from 250 to over 4,000 milligrams Cypermethrin in the U.S. in California (1993) per kilogram (mg/kg) of body weight. This sugar beets other (1,521 pounds) (946 pounds) variability is partly due to the solvents used cotton in the test, and partly due to variability in (1,652 pounds) the proportions of cypermethrin’s isomers. In mice, it can vary from 80 to almost 800 mg/kg.12 The U.S. Environmental Protec- lettuce tion Agency (EPA) uses LD s of 250-300 (18,795 50 pounds) mg/kg.14 This puts cypermethrin in toxic- Cotton (total annual use 46,000 pounds) ity category II (“Warning”).2 Juvenile rats are almost twenty times more susceptible to cypermethrin than structural pest control adults. This is probably due to incomplete (38,541 pounds) development of detoxification enzymes.15 California Environmental Protection Agency. Synergy: Pyrethroid insecticides, includ- Dept. of Pesticide Regulation. Information Services Branch. 1995. Pesticide use report. ing cypermethrin, are broken down by en- Annual 1993. Indexed by chemical. Sacramento, zymes called esterases. The same enzymes CA. (June.) are inhibited by organophosphate insecti- Lettuce (total annual use 21,600 pounds) cides. If the two kinds of insecticides are In California, cypermethrin’s predominant use is for structural pest control: killing termites, used together, cypermethrin will not be bro- cockroaches, and fleas in homes and other ken down as fast as it normally is . The buildings. result is that the two kinds of insecticides are synergistic: the toxicity of cypermethrin lease the neurotransmitter acetylcholine and in combination with an organophosphate stimulate other nerves.6 insecticide is greater than the toxicity of Cypermethrin has other effects on the either insecticide alone.16 nervous system. It inhibits the γ- Skin and Eye Irritation: Cypermethrin Onions (total annual use 7,500 pounds) aminobutyric acid receptor, causing excit- and some cypermethrin-containing prod- ability and convulsions.7 In addition, it in- ucts are skin sensitizers. This means that Sources: U.S. Dept. of Agriculture. National Agricultural hibits calcium uptake by nerves8 and inhib- when cypermethrin is applied to skin sev- Statistics Service. Economics Research 9 Service.1996. Agricultural chemical usage: its monoamine oxidase, an enzyme that eral times, later applications will have a 1995 field crops summary. Washington, D.C. (March.) breaks down neurotransmitters. more serious response than the first U.S. Dept. of Agriculture. National Agricultural Cypermethrin also affects an enzyme not application.17 Statistics Service. Economics Research Service.1995. Agricultural chemical usage. directly involved with the nervous system, Cypermethrin has caused the cornea of Vegetables: 1994 summary. Washington, D.C. 17 (July.) adenosine triphosphatase. It is involved in laboratory animals to become opaque. cellular energy production, transport of Effects on the Immune metal atoms, and muscle contractions.10 Cypermethrin’s most important agricultural System uses are on cotton, lettuce, and onions. Acute Toxicity In both rabbits and rats, cypermethrin Cypermethrin, like all synthetic pyre- Humans: Symptoms of cypermethrin has been shown to suppress immune sys- throids, kills insects by disrupting normal poisoning in humans include facial burn- tem function. Rabbits fed cypermethrin pro- functioning of the nervous system. In in- ing and tingling (called paraesthesia1), diz- duced fewer antibodies to a Salmonella bac- sects, as well as all other animals including ziness, headaches, nausea, anorexia, fatigue,11 teria than did unexposed animals. They also humans, nerve impulses travel along nerves and loss of bladder control.12 With greater produced a smaller reaction to a tuberculin when the nerves become momentarily per- exposure, symptoms include muscle twitch- skin test. Some effects were significant at 11 18 meable to sodium atoms, allowing sodium ing, drowsiness, coma, and seizures. doses of 1/40 of the LD50. (See Figure to flow into the nerve. Pyrethroids delay Laboratory Animals: Symptoms of 4.) the closing of the “gate” that allows the cypermethrin toxicity in laboratory animals Rats fed cypermethrin produced fewer sodium flow.5 This results in multiple nerve include pawing, burrowing, salivation, trem- antibodies to foreign blood cells and for- impulses instead of the usual single one. In ors, writhing, and seizures.13 eign proteins. Effects were significant at 18 turn, these impulses cause the nerve to re- The median oral lethal dose (the dose doses of 1/10 of the LD50. NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP 16 P.O. BOX 1393, EUGENE, OREGON 97440 / (541)344-5044 JOURNAL OF PESTICIDE REFORM/ SUMMER 1996 • VOL.16, NO. 2 Effects on Reproduction male mice.25 rabbits, it caused pathological changes in the 12 Exposure of pregnant laboratory animals Two recent studies have demonstrated thymus, liver, adrenal glands, lungs, and skin. molecular mechanisms by which cypermethrin to cypermethrin can affect their offspring. Feed- Occupational Exposure ing pregnant rabbits cypermethrin resulted in might be involved in causing cancer. One study looked at “gap junctional intercellular com- In the U.S., most occupational exposure to a small increase in the number of organ and 26 skeletal abnormalities in their offspring.1 Rats munication.” This process plays “important cypermethrin comes from its uses to kill home exposed prenatally showed developmental de- roles in maintenance, growth, and differentia- and building pests. Structural pest control op- lays: events such as the emergence of a tooth, tion of cells” and is inhibited by many carci- erators are exposed to cypermethrin; in Cali- opening of eyes, and development of particu- nogenic agents. The study showed that fornia, where reporting of pesticide-related ill- lar reflexes occurred up to three days later in cypermethrin, four other synthetic pyrethroid nesses is more complete than in other states, exposed rats than in unexposed rats.19 insecticides, and the organochlorine insecticide cypermethrin was the fourth most common DDT all were inhibitory.26 A second study cause of pesticide-related illnesses among this Male reproduction is also affected by 28 cypermethrin. In mice, the proportion of ab- showed that, in addition to inhibiting