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EXTOXNET PIP-PARAQT T Page 2 of 3
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<br /> • Chronic toxicity:As indicated above,repeated exposures may cause skin imitation,sensitization,or ulcerations on
<br /> ion contact[58,87].In animal studies,rats showed no effects after being exposed for 2 years to paraquat at doses of 1.25
<br /> mg/kg/day[8].Dogs,however,developed lung problems after being exposed for 2 years at high doses(above 34
<br /> mg/kg/day)[8].In a study of 30 workers spraying paraquat over a 12-week period,approximately one-half had minor
<br /> irritation of the eyes and nose[8].Of 296 spray operators with gross and prolonged skin exposure,55 had damaged
<br /> ` fingernails as indicated by discoloration,nail deformities,or loss of nails[8].
<br /> • Reproductive effects:In a long-term rat study at doses up to 5 mg/kg/day,no adverse reproductive effects were
<br /> reported[111].However,paraquat dichloride injected intraperitoneally at 3 mg/kg/day on days 8 to 16 of gestation
<br /> increased fetal mortality in rats[8].Hens given high levels of paraquat in their drinking water for 14 days produced
<br /> an increased percentage of abnormal eggs[8].It is unlikely to cause reproductive effects in humans at expected
<br /> exposure levels.
<br /> • Teratogenic effects:Offspring of mice dosed with high doses of paraquat during the organ-forming period of
<br /> ` pregnancy had less complete bone development than the mice given lower doses[111].Offspring of rats given similar
<br /> treatment showed no developmental defects at any dose,but fetal and maternal body weights were lower than normal
<br /> [I I I].Other studies of paraquat using rabbits and mice have shown no teratogenic effects[8].The weight of evidence
<br /> suggests that paraquat does not cause birth defects at doses which might reasonably be encountered.
<br /> r • Mutagenic effects:Paraquat has been shown to be mutagenic in microorganism tests and mouse cell assays[8].It
<br /> was unclear what levels of exposure are necessary to produce these effects.
<br /> Carcinogenic effects:Mice fed paraquat dichloride for 99 weeks at high levels did not show cancerous growths
<br /> [112].Rats fed high doses for 113(male)or 124 weeks(female)developed lung,thyroid,skin,and adrenal tumors
<br /> ..
<br /> [I I I].Thus,the evidence regarding carcinogenic effects of paraquat is inconclusive.
<br /> • Organ toxicity:Paraquat affects the lungs,heart,liver,kidneys,cornea,adrenal glands,skin,and digestive system.
<br /> • Fate in humans and animals:Paraquat is not readily absorbed from the stomach,and is even more slowly absorbed
<br /> across the skin.Oral doses of paraquat in rats are excreted mainly in the feces,while paraquat injected into the
<br /> abdomen leaves through urine[8].In the stomach and gastrointestinal tract,paraquat metabolites may be more readily
<br /> absorbed than the parent compound,but their identities and toxicities are unknown[I I I].Paraquat may concentrate in
<br /> lung tissue,where it can be transformed to highly reactive and potentially toxic forms[87].In one study,farm animals
<br /> ` excreted over 90%of the administered paraquat within a few days.It was slightly absorbed and metabolized in the
<br /> gastrointestinal tract.Milk and eggs contained small amounts of two paraquat metabolites[58].
<br /> Ecological Effects:
<br /> • Effects on birds:The compound is moderately toxic to birds,with reported acute oral LD50 values of 981 mg/kg and
<br /> 970 mg/kg in bobwhite and Japanese quail,respectively[58].The reported 5-to 8-day dietary LC50 value for the
<br /> ` compound is 4048 ppm in mallards[58].
<br /> • Effects on aquatic organisms:Paraquat is slightly to moderately toxic to many species of aquatic life,including
<br /> rainbow trout,bluegill,and channel catfish[58,8].The reported 96-hour LC50 for paraquat is 32 mg/L in rainbow
<br /> trout,and 13 mg/L in brown trout[58].The LC50 for the aquatic invertebrate Daphnia pulex is 1.2 to 4.0 mg/L[8].In
<br /> rainbow trout exposed for 7 days to paraquat,the chemical was detected in the gut and liver,but not in the meat of the
<br /> fish.Aquatic weeds may bioaccumulate the compound.In one study,4 days after paraquat was applied as an aquatic
<br /> herbicide,weeds sampled showed significant residue levels[87].At high levels,paraquat inhibits the photosynthesis
<br /> of some algae in stream waters[87].
<br /> • Effects on other organisms:Paraquat is nontoxic to honey bees[112].
<br /> Environmental Fate:
<br /> • Breakdown in soil and groundwater:Paraquat is highly persistent in the soil environment,with reported field half-
<br /> lives of greater than 1000 days[11,58].The reported half-life for paraquat in one study ranged from 16 months
<br /> r, (aerobic laboratory conditions)to 13 years(field study)[113].Ultraviolet light,sunlight,and soil microorganisms can
<br /> degrade paraquat to products which are less toxic than the parent compound.The strong affinity for adsorption by soil
<br /> particles and organic matter may limit the bioavailability of paraquat to plants,earthworms,and microorganisms
<br /> [11,58].The bound residues may persist indefinitely and can be transported in runoff with the sediment.Paraquat is
<br /> .. not significantly mobile in most soils[8].That which does not become associated with soil particles can be
<br /> decomposed to a nontoxic end product by soil bacteria[32].Thus,paraquat does not present a high risk of
<br /> groundwater contamination.Of 721 groundwater samples analyzed,only one contained paraquat,at a concentration
<br /> of 20 mg/L[I 11].
<br /> • Breakdown in water:Paraquat will be bound to suspended or precipitated sediment in the aquatic environment,and
<br /> may be even more highly persistent than on land due to limited availability of oxygen.It had a half-life in a laboratory
<br /> ir.
<br /> http://extoxnet.orst.edu/pips/paraquat.htm 9/26/2004
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