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EXTOXNET PIP -PARAQUAT Page 2 of 4 followed by gastrointestinal tract irritation, resulting in abdominal pain, loss of appetite, nausea, vomiting, and diarrhea [8]. Other toxic effects include thirst, shortness of breath, rapid heart rate, kidney failure, lung sores, and liver injury [32]. Some symptoms may not occur until days after exposure. Persons with lung problems may be at increased risk from exposure. Many cases of illness and/or death have been reported in humans. The estimated lethal dose(via ingestion) for paraquat in humans is 35 mg/kg [8]. A maximum of 3.5 mg/hour could be absorbed through the dermal or respiratory route without damage [32]. • Chronic toxicity: As indicated above,repeated exposures may cause skin irritation, sensitization, or ulcerations on contact [58,87]. In animal studies,rats showed no effects after being exposed for 2 years to paraquat at doses of 1.25 mg/kg/day [8]. Dogs, however, developed lung problems after being exposed for 2 years at high doses (above 34 mg/kg/day) [8]. In a study of 30 workers spraying paraquat over a 12-week period, approximately one-half had minor irritation of the eyes and nose [8]. Of 296 spray operators with gross and prolonged skin exposure, 55 had damaged fingernails as indicated by discoloration,nail deformities, or loss of nails [8]. • Reproductive effects: In a long-term rat study at doses up to 5 mg/kg/day, no adverse reproductive effects were reported [111]. However, paraquat dichloride injected intraperitoneally at 3 mg/kg/day on days 8 to 16 of gestation increased fetal mortality in rats [8]. Hens given high levels of paraquat in their drinking water for 14 days produced an increased percentage of abnormal eggs [8]. It is unlikely to cause reproductive effects in humans at expected exposure levels. • Teratogenic effects: Offspring of mice dosed with high doses of paraquat during the organ-forming period of pregnancy had less complete bone development than the mice given lower doses [111]. Offspring of rats given similar treatment showed no developmental defects at any dose, but fetal and maternal body weights were lower than normal [111]. Other studies of paraquat using rabbits and mice have shown no teratogenic effects [8]. The weight of evidence suggests that paraquat does not cause birth defects at doses which might reasonably be encountered. • Mutagenic effects: Paraquat has been shown to be mutagenic in microorganism tests and mouse cell assays [8]. It was unclear what levels of exposure are necessary to produce these effects. • Carcinogenic effects: Mice fed paraquat dichloride for 99 weeks at high levels did not show cancerous growths [112]. Rats fed high doses for 113 (male) or 124 weeks (female) developed lung, thyroid, skin, and adrenal tumors [111]. Thus,the evidence regarding carcinogenic effects of paraquat is inconclusive. • Organ toxicity: Paraquat affects the lungs, heart, liver, kidneys, cornea, adrenal glands, skin, and digestive system. • Fate in humans and animals: Paraquat is not readily absorbed from the stomach, and is even more slowly absorbed across the skin. Oral doses of paraquat in rats are excreted mainly in the feces, while paraquat injected into the abdomen leaves through urine [8]. In the stomach and gastrointestinal tract, paraquat metabolites may be more readily absorbed than the parent compound,but their identities and toxicities are unknown [111]. Paraquat may concentrate in lung tissue, where it can be transformed to highly reactive and potentially toxic forms [87]. In one study, farm animals excreted over 90% of the administered paraquat within a few days. It was slightly absorbed and metabolized in the gastrointestinal tract. Milk and eggs contained small amounts of two paraquat metabolites [58]. Ecological Effects: • Effects on birds: The compound is moderately toxic to birds,with reported acute oral LD50 values of 981 mg/kg and 970 mg/kg in bobwhite and Japanese quail,respectively [58]. The reported 5- to 8-day dietary LC50 value for the compound is 4048 ppm in mallards [58]. • Effects on aquatic organisms: Paraquat is slightly to moderately toxic to many species of aquatic life, including rainbow trout,bluegill, and channel catfish [58,8]. The reported 96-hour LC50 for paraquat is 32 mg/L in rainbow 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 rainbow trout exposed for 7 days to paraquat, the chemical was detected in the gut and liver,but not in the meat of the fish. Aquatic weeds may bioaccumulate the compound. In one study, 4 days after paraquat was applied as an aquatic herbicide, weeds sampled showed significant residue levels [87]. At high levels, paraquat inhibits the it http://extoxnet.orst.edu/pips/paraquat.htm 3/13/2006