toxicological profile for malathion - Agency for Toxic Substances and ...

MALATHION 72
3. HEALTH EFFECTS
an uncommon finding following organophosphate intoxication. Interestingly, no such congestion was
seen in the chronic studies with much larger doses.
Dermal Effects. No studies were located regarding dermal effects in humans following oral exposure
to malathion. The only information regarding dermal effects in animals following exposure to malathion
is that provided in the long-term bioassays, which reported no gross or microscopic alterations in the skin
from rats or mice treated with malathion in the diet for periods between 80 and 103 weeks. Rats were
dosed with up to 622 mg/kg/day malathion (NCI 1978, 1979a) and mice with up to 2,980 mg/kg/day (NCI
1978).
Ocular Effects. Pupillary constriction and blurred vision were observed in many cases of malathion
intoxication (Amos and Hall 1965; Crowley and Johns 1966; Ekin 1971; Jušić and Milić 1978;
Matsukawa et al. 1997; Monje Argiles et al. 1990; Rivett and Potgieter 1987; Sudakin et al. 2000). These
effects are typical signs of organophosphate poisoning resulting from stimulation of parasympathetic
autonomic postganglionic nerves.
The only information regarding ocular effects in animals following oral exposure to malathion is that no
significant ocular effects were observed in Fischer-344 rats administered up to 868 mg/kg/day of
malathion (97.1% pure) in the diet for 2 years (Daly 1996a) (retinal degeneration has been observed in
rats treated long-term with other organophosphates such as fenthion, see Dementi [1993]).
Body Weight Effects. No information was located regarding body weight effects in humans
following oral exposure to malathion. Of several studies providing information on body weight in
animals after acute oral administration of malathion, only two studies in rats reported significant effects.
Ojha et al. (1992) reported a 17% decrease in final weight relative to controls in rats administered
approximately 593 mg/kg/day malathion (unspecified purity) in the food for 7 days. This decrease was
accompanied by a significant decrease in food consumption; the NOAEL was 451 mg/kg/day. The other
study reported a decrease of 22% in body weight gain during pregnancy in rats administered
500 mg/kg/day malathion (98% pure) by gavage on gestation days 6, 10, and 14 (Prabhakaran et al.
1993). In this case, food intake was not affected by treatment with malathion. Other representative acuteduration
studies in rats reported NOAELs of 225 mg/kg/day after 6 days gavage administration of
malathion, and 286 mg/kg/day after 14 days of administration of malathion in drinking water (Lox 1985).
A NOAEL of 715 mg/kg/day (only dose tested) was reported in a study in mice given a single gavage
dose of malathion and monitored for 5 days (Rodgers et al. 1986). Administration of 100 mg/kg/day