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EXTOXNET PIP - CHLORPYRIFOS Page 2 of 4
<br /> respiratory ailments, recent exposure to cholinesterase inhibitors, cholinesterase impairment, or liver malfunction
<br /> are at increased risk from exposure to chlorpyrifos. Some organophosphates may cause delayed symptoms
<br /> beginning 1 to 4 weeks after an acute exposure which may or may not have produced immediate symptoms [2]. In
<br /> such cases, numbness, tingling, weakness, and cramping may appear in the lower limbs and progress to
<br /> incoordination and paralysis. Improvement may occur over months or years, and in some cases residual impairment
<br /> will remain [2]. Plasma cholinesterase levels activity have been shown to be inhibited when chlorpyrifos particles
<br /> are inhaled [8]. The oral LD50 for chlorpyrifos in rats is 95 to 270 mg/kg [2,13]. The LD50 for chlorpyrifos is 60
<br /> mg/kg in mice, 1000 mg/kg in rabbits, 32 mg/kg in chickens, 500 to 504 mg/kg in guinea pigs, and 800 mg/kg in
<br /> sheep [2,13,44]. The dermal LD50 is greater than 2000 mg/kg in rats, and 1000 to 2000 mg/kg in rabbits [2,13,45].
<br /> The 4-hour inhalation LC50 for chlorpyrifos in rats is greater than 0.2 mg/L [46].
<br /> • Chronic toxicity: Repeated or prolonged exposure to organophosphates may result in the same effects as acute
<br /> exposure including the delayed symptoms. Other effects reported in workers repeatedly exposed include impaired
<br /> memory and concentration, disorientation, severe depressions, irritability, confusion, headache, speech difficulties,
<br /> delayed reaction times, nightmares, sleepwalking, and drowsiness or insomnia. An influenza-like condition with
<br /> headache, nausea,weakness, loss of appetite, and malaise has also been reported [8]. When technical chlorpyrifos
<br /> was fed to dogs for 2 years, increased liver weight occurred at 3.0 mg/kg/day. Signs of cholinesterase inhibition
<br /> occurred at 1 mg/kg/day. Rats and mice given technical chlorpyrifos in the diet for 104 weeks showed no adverse
<br /> effects other than cholinesterase inhibition [43]. Two-year feeding studies using doses of 1 and 3 mg/kg/day of
<br /> chlorpyrifos in rats showed moderate depression of cholinesterase. Cholinesterase levels recovered when the
<br /> experimental feeding was discontinued [2]. Identical results occurred in a 2-year feeding study with dogs. No long
<br /> term health effects were seen in either the dog or rat study [2,47]. A measurable change in plasma and red blood
<br /> cell cholinesterase levels was seen in workers exposed to chlorpyrifos spray. Human volunteers who ingested 0.1
<br /> mg/kg/day of chlorpyrifos for 4 weeks showed significant plasma cholinesterase inhibition [47].
<br /> • Reproductive effects: Current evidence indicates that chlorpyrifos does not adversely affect reproduction. In two
<br /> studies,no effects were seen in animals tested at dose levels up to 1.2 mg/kg/day [8]. No effects on reproduction
<br /> occurred in a three-generation study with rats fed dietary doses as high as 1 mg/kg/day [43,47]. In another study in
<br /> which rats were fed 1.0 mg/kg/day for two generations, the only effect observed was a slight increase in the number
<br /> of deaths of newborn offspring [2].
<br /> • Teratogenic effects: Available evidence suggests that chorpyrifos is not teratogenic. No teratogenic effects in
<br /> offspring were found when pregnant rats were fed doses as high as 15 mg/kg/day for 10 days. When pregnant mice
<br /> were given doses of 25 mg/kg/day for 10 days, minor skeletal variations and a decrease in fetal length occurred
<br /> [43,45]. No birth defects were seen in the offspring of male and female rats fed 1.0 mg/kg/day during a three-
<br /> generation reproduction and fertility study [2,47].
<br /> • Mutagenic effects: There is no evidence that chlorpyrifos is mutagenic. No evidence of mutagenicity was found in
<br /> any of four tests performed [43].
<br /> • Carcinogenic effects: There is no evidence that chlorpyrifos is carcinogenic. There was no increase in the
<br /> incidence of tumors when rats were fed 10 mg/kg/day for 104 weeks, nor when mice were fed 2.25 mg/kg/day for
<br /> 105 weeks [43].
<br /> • Organ toxicity: Chlorpyrifos primarily affects the nervous system through inhibition of cholinesterase, an enzyme
<br /> required for proper nerve functioning.
<br /> • Fate in humans and animals: Chlorpyrifos is readily absorbed into the bloodstream through the gastrointestinal
<br /> tract if it is ingested, through the lungs if it is inhaled, or through the skin if there is dermal exposure [8]. In
<br /> humans, chlorpyrifos and its principal metabolites are eliminated rapidly [2]. After a single oral dose, the half-life
<br /> of chlorpyrifos in the blood appears to be about 1 day [41]. Chlorpyrifos is eliminated primarily through the kidneys
<br /> [8]. Following oral intake of chlorpyrifos by rats, 90%is removed in the urine and 10% is excreted in the feces [13].
<br /> It is detoxified quickly in rats, dogs, and other animals [8]. The major metabolite found in rat urine after a single
<br /> oral dose is trichloropyridinol (TCP). TCP does not inhibit cholinesterase and it is not mutagenic [8]. Chlorpyrifos
<br /> does not have a significant bioaccumulation potential [8]. Following intake, a portion is stored in fat tissues but it is
<br /> eliminated in humans, with a half-life of about 62 hours [2]. When chlorpyrifos (Dursban) was fed to cows,
<br /> unchanged pesticide was found in the feces, but not in the urine or milk [48]. However, it was detected in the milk
<br /> of cows for 4 days following spray dipping with a 0.15% emulsion. The maximum concentration in the milk was
<br /> http://extoxnet.orst.edu/pips/chlorpyr.htm 3/13/200(
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