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l:X"I OXNG"t 1'[P-FE NnMIPI IOS -):Hace.orst.edu/cgi-bin/mt's/01/pips/1'enamiph.htm [8,13]. The acute dermal toxicity of the compound is also high, with reported dermal LD50 values of 72 to 154 mg/kg in rats [8,13]. The inhalation toxicity of the compound is also high, with reported inhalation LC50 values in rats of 0.11 to 0.17 mg/L [8,13]. Longer exposures at moderately lower concentrations also caused rat mortality [8]. The compound has the potential to cause significant eye damage at acute exposure levels. It is nonirritating to the skin [13]. Symptoms of acute toxic exposure to the nematicide are consistent with those of other organophosphate compounds and include difficulty in breathing, diarrhea, urination, and slowness of the heart. Other Symptoms include muscle twitching and tremors [8,13]. • Chronic toxicity: A number of long-term feeding studies have been conducted with this compound on several different species of animals. In dogs, dietary doses of 0.0125 to 0.25 mg/kg/day over '? years produced depressions in cholinesterase activity at middle doses and above. No effects were noted in the liver or in blood chemistry even at the highest dose [8]. Rats exposed to 1.5 mg/kg/day over 2 years experienced increases in thyroid gland and lung weights in females, and increased heart weight in males. There were no organ weight changes noted in the rats at doses below 0.5 mg/kg/day [64]. Brain weights have also been affected by exposure to moderate amounts of the compound [8]. Two studies have been conducted on the potential risk to pesticide workers (loaders and applicators) from the use of Nemacur. One study concluded that occupational exposure levels were more than 100 times lower than the level which causes cholinesterase inhibition in animals and thus the use of the compound did not pose a significant risk to the users [8]. Another study concluded that the main threat to applicators was through the skin on the hands. However, the levels of exposure on the hands were significantly below the level that had caused chronic toxicity in mice. It was concluded that the pesticide could be used safely [65]. • Reproductive effects: Both male and female rats fed moderate to high doses of fenamiphos (0.15 to 1.5 mg/kg/day) over three generations showed no compound-related reproductive effects at the middle doses tested (0.5 mg/kg/day). At the higher doses the second generation of pups showed a decrease in body weight gain. This effect was not seen in the third generation [64]. It is unlikely that this compound would cause reproductive effects in humans. • Teratogenic effects: A single study of pregnant rats fed fenamiphos during gestation over a range of doses (up to 1 mg/kg/day) showed a decrease in the maternal weight at doses of 0.3 mg/kg/day and above. At the highest dose a higher number of the pups from the exposed group had died relative to the unexposed controls, and the pups which survived had decreased weights [64]. In tests with pregnant rabbits fed up to 0.4 mg/kg, no birth defects were noted [8]. However, another reference stated that teratogenic studies were positive in rabbits, though the effects in the offspring were induced at doses much higher than those that cause maternal toxicity [8]. The results from these studies suggest that teratogenic effects in humans are unlikely. • Mutagenic effects: A number of studies evaluating the mutagenic potential of fenamiphos have all shown the compound to be nonmutagenic. The test subjects included bacterial cells and male mice [8,64]. • Carcinogenic effects: Two studies, one conducted with mice and the other with rats, indicated that fenamiphos is not carcinogenic [8,64]. One study was conducted for 1 1/2 years at very high levels (up to 7.5 mg/kg/day in mice) and the other study was conducted over 2 years (up to 1.5 mg/kg/day in rats) [64]. • Organ toxicity: Target organs identified in studies of test animals and exposed workers are the central nervous system, heart, lungs, and thyroid. • Fate in humans and animals: Fenamiphos is readily absorbed through the digestive tract and lungs. One study placed the amount absorbed near 95% of the ingested dose. The compound is rapidly broken down within the organism, and the by-products are excreted in the urine. The majority of a dose was recovered in urine within 15 hours after treatment [65]. ot'a S112"00 2:0� I'M