Trade and Other Names: Trade names for trichlorfon include Anthon, Bovinos, Briten, Chlorophos, Ciclosom, Dipterex, Ditrifon, Dylox, Dyrex, Equino-Aid, Foschlor, Leivasom, Neguvon, Masoten, Pronto, Phoschlor, Proxol, Totalene, Trichlorophene, Trichlorophon, Trinex, Tugon and Vermicide Bayer 2349. The common name used in Great Britain is trichlorphon, in Turkey is dipterex, and in the former U.S.S.R. is chlorofos. When this material is used as a drug, it is called metrifonate or metriphonate.
Regulatory Status: Trichlorfon is classified by the U.S. Environmental Protection Agency (EPA) as a General Use Pesticide (GUP). It is in toxicity class II - moderately toxic. Products containing trichlorfon bear the Signal Word WARNING.
Introduction: Trichlorfon is an organophosphate insecticide used to control cockroaches, crickets, silverfish, bedbugs, fleas, cattle grubs, flies, ticks, leafminers, and leaf-hoppers. It is applied to vegetable, fruit, and field crops; livestock; ornamental and forestry plantings; in agricultural premises and domestic settings; in greenhouses, and for control of parasites of fish in designated aquatic environments. It is also used for treating domestic animals for control of internal parasites [2,6]. Trichlorfon is available in dust, emulsifiable concentrate, granular, fly bait, and soluble powder formulations with percent active ingredient ranging from 40% (soluble powder) to 98% (technical). Trichlorfon is a selective insecticide, meaning that it kills selected insects, but spares many or most other organisms. Trichlorfon is toxic to target insects through direct applications and via ingestion.
Formulation: Trichlorfon is available in dust, emulsifiable concentrate, granular, fly bait, and soluble powder formulations with percent active ingredient ranging from 40 (soluble powder) to 98% (technical).
Acute toxicity: Trichlorfon is moderately toxic by ingestion or dermal absorption. As with all organophosphates, trichlorfon is readily absorbed through the skin. Skin sensitivity (allergies) can result from dermal exposure . Trichlorfon decreases activity of the cholinesterase enzyme which is necessary for normal nervous system function. Symptoms of acute exposure include headache, giddiness, nervousness, blurred vision, weakness, nausea, cramps, loss of muscle control or reflexes, convulsion, or coma . It has been suggested that impurities or additives may be associated with some cases of delayed polyneuropathy (damage to nerve cells) attributed to ingestion of large amounts of trichlorfon . These delayed symptoms may occur following recovery from the initial acute effects. Pure trichlorfon is reported to be less toxic than the technical material [2,8]. The oral LD50 for trichlorfon is 450 to 650 mg/kg in rats and 300 to 860 mg/kg in mice . Other reported oral LD50 values are 94 mg/kg in cats, 400 mg/kg in dogs, 420 mg/kg in dogs, and 160 mg/kg in rabbits . The dermal LD50 is 2000 to 5000 mg/kg in rats [2,8], and 1500 to greater than 2100 mg/kg in rabbits [2,41]. The 4-hour inhalation LC50 for trichlorfon in rats is greater than 0.5 mg/L .
Chronic toxicity: Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure. Other effects reported in workers repeatedly exposed include impaired memory and concentration, disorientation, severe depressions, irritability, confusion, headache, speech difficulties, delayed reaction times, nightmares, sleepwalking, and drowsiness or insomnia. An influenza-like condition with headache, nausea, weakness, loss of appetite, and malaise has also been reported . When 45 mg/kg/day was administered to dogs for 3 months, serum cholinesterase was reduced to 60% of normal [2,8]. A dietary level of about 10.5 mg/kg/day for 12 weeks produced a similar effect [2,8]. During a 60-day testing period with repeated doses of trichlorfon at 100 mg/kg/day, the cholinesterase activity of rats was reduced to less than half of normal levels. Doses of 50 mg/kg/day reduced the activity to 50 to 75% of normal levels [2,8]. Trichlorfon produced no pathological changes in rats that were fed 500 mg/kg/day of the insecticide for 1 year . Edema (excessive accumulation of fluid) of the brain, congestion of organs, degeneration of various parts of the liver, inflammation of the lungs, and heart muscle changes were observed in rats given very high daily oral doses of 300 mg/kg/day technical trichlorfon for 5 days. Brain disturbances and changes in the liver, kidneys, spleen, lungs, and testicles were seen in bulls that were given oral doses of 1, 2, or 5 mg/kg formulated trichlorfon (Chlorophos) daily, or 5 mg/kg at weekly intervals for 6 months .
Reproductive effects: Trichlorfon is suspected of having negative reproductive effects . An increased number of embryonic deaths, a decreased number of live fetuses, and an increased number of fetal abnormalities were observed in rats given a single oral dose of 80 mg/kg body weight, by stomach tube, on day 13 of pregnancy . During a three-generation study of the effect of trichlorfon on rat reproduction, a dose of about 150 mg/kg/day resulted in a marked decrease in the rate of pregnancy, and underdeveloped rat pups at birth, none of which survived to weaning. A dose of 50 mg/kg/day reduced the number of pups per litter, as well as the weight of individual pups. Doses of 15 mg/kg/day had no detectable effect on reproduction [2,8]. Once in the bloodstream, trichlorfon may cross the placenta . It is unlikely that reproductive effects will occur in humans at expected exposure levels.
Teratogenic effects: Trichlorfon caused inability to walk and tremors in pig offspring if administered at day 55 at a dose of 55 mg/kg [2,8]. Dipterex was teratogenic when given to pregnant rats through a stomach tube at a dose level of 480 mg/kg/day, on days 6 through 15 of pregnancy, but not when administered only on days 8 or 10 of pregnancy . Teratogenic effects were also seen in hamsters given 400 mg/kg/day on days 7 through 11 of pregnancy . There was no evidence of teratogenesis in a three-generation study with rats fed dietary dose of as high as 150 mg/kg/day , or in a metabolite study of rabbits at doses of 50 to 75 mg/kg/day [2,8]. Thus the evidence suggests that reproductive effects occur only at high doses and are unlikely in humans at expected exposure levels.
Mutagenic effects: Studies indicate that trichlorfon, or its degradation products, can be mutagenic in bacterial and mammalian cells . The insecticide produced mutations in mice when it was given in the highest tolerable single dose and in smaller, repeated doses [2,8].
Carcinogenic effects: One study suggests that oral doses of 37.5 to 75 mg/kg/day of trichlorfon contribute to the production of tumors in rats . Carcinogenic effects were also seen in rats given oral doses of 186 mg/kg or intramuscular doses of 183 mg/kg/day for 6 weeks . Benign tumors called 'papillomas' developed in the lining of the forward portion of the stomach when trichlorfon was administered to rats orally or subcutaneously. Rats that survived for 6 months had varying degrees of liver damage [2,8]. However, no evidence of carcinogenicity was found in rats given the insecticide orally or intraperitoneally for 90 weeks [2,8]. In addition, no evidence of carcinogenicity was observed when trichlorfon was administered orally, intraperitoneally, or dermally to mice [2,8]. Thus, the carcinogenic data are inconclusive.
Organ toxicity: Trichlorofn primarily affects the nervous system through inhibition of cholinesterase, and enzyme required for proper nerve functioning. Other target organs include the liver, lungs, and bone marrow (blood-forming tissue).
Fate in humans and animals: The absorption, distribution, and excretion of trichlorfon is rapid. About 70 to 80% of a dose administered orally to mice was excreted during the first 12 hours following treatment . Similar rapid elimination was seen in pigs following intraperitoneal injection [2,8]. A hypothesized metabolite of trichlorfon, dichlorvos (DDVP), was found in some body tissues of exposed cows. Trichlorfon was found in cows' milk following "pour-on" applications of the insecticide [2,8].
Effects on birds: Trichlorfon is moderately to highly toxic to birds. Signs of intoxication in birds include regurgitation, imbalance, trembling, slowness, lack of movement, and wing-beat convulsions. Signs of poisoning appear as soon as 10 minutes after exposure, and death usually occurs within 30 minutes to 3 hours of treatment . The dietary LC50 for trichlorfon is 700 to 800 ppm in bobwhites. The estimated dietary LC50 is about 1800 ppm in 2-week-old Japanese quail that were fed treated feed for 5 days, followed by untreated feed for 3 days . Some 77% of exposed hen embryos were killed when 100 ppm of trichlorfon (in acetone) was injected into their eggs [2,8]. The acute oral LD50 for trichlorfon is 36.8 mg/kg in mallards, 22.4 mg/kg in bobwhite quail, 59.3 in California quail, 95.9 mg/kg in male pheasant, and 23 mg/kg in rock doves .
Effects on aquatic organisms: Trichlorfon, in both technical and formulated forms, is very highly toxic to many aquatic species such as Daphnia, stoneflies, crayfish, and several freshwater fish species [14,15]. Reported LC50 (96-hour) values are 0.18 mg/L (48-hour) in Daphnia, 0.01 mg/L in stoneflies, 7.8 mg/L in crayfish, 1.4 mg/L in rainbow trout, 2.5 mg/L in brook trout, 0.88 mg/L in channel catfish and 0.26 mg/L in bluegill . Toxicity in the field can be affected by many factors including temperature, pH, and water hardness, which may have different effects across species [14,15]. In some species, temperature differences of 10 C could result in differences of 7 to 60 fold in observed 96-hour LC50 values . Effects of changing pH from 6.5 to 8.5 resulted in changes of 13 to 20 fold in several species . Generally, toxicity increased (i.e., observed LC50 was lower) with higher temperature and higher pH. Studies did not show a potential for trichlorfon to accumulate in fish .
Effects on other organisms: Trichlorfon has moderate to high acute toxicity toward certain beneficial or non-target insects . This pesticide may be toxic to other wildlife . Data indicate that trichlorfon has a low toxicity to bees; it can be used around bees with minimum injury .
Breakdown in soil and groundwater: Trichlorfon breaks down, or degrades, rapidly in aerobic soils, with a half-life of between 3 and 27 days. An average half-life of 10 days has been reported . Its major breakdown product is dichlorvos (DDVP) . Trichlorfon is of low persistence in soil environments. Trichlorfon does not adsorb strongly to soil particles, is readily soluble in water, and is very mobile in soils of varying textures and organic contents. It is therefore likely to contaminate groundwater . Soil organic matter content does not appear to influence trichlorfon's movement in soil .
Breakdown in water: Trichlorfon degrades rapidly in alkaline pond water (pH 8.5). Approximately 99% of applied trichlorfon was broken down within 2 hours. It was stable in the same pond water kept under acidic (pH 5.0) conditions for 2 hours. The major breakdown product of trichlorfon in water is dichlorvos (DDVP) . This insecticide was shown to persist at detectable levels for 526 days in water at 20 C .
Breakdown in vegetation: Studies on the dissipation of trichlorfon in forest environments indicate that it does not persist in leaves or leaf-litter . The approximate residual period is 7 to 10 days on plants. Injury has been reported on the foliage of apples, and on carnations and zinnias .
Appearance: Trichlorfon is a pale clear, white, or yellow crystalline solid with an ethyl ether odor. Trichlorfon is a solid at room temperature .