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

MALATHION 73
3. HEALTH EFFECTS
malathion (98% pure) to mice on lactation days 1–14 had no significant effect on body weight gain
(Chhabra et al. 1993).
In intermediate-duration oral studies in rats, the only one that reported a significant effect of malathion on
body weight was NCI (1979a) in which female Fischer-344 rats showed a 50% reduction in final body
weight after administration of approximately 1,399 mg/kg/day malathion (95% pure) in the diet for
13 weeks; no significant effects were seen in males at this dose level or in females dosed approximately
700 mg/kg/day. No information on food intake was provided in the NCI (1979a) study. Other NOAELs
in rats include 75 and 29 mg/kg/day in 90-day (Desi et al. 1976) and 6-week (Foster 1968) dietary studies,
respectively, and 20 mg/kg/day in a 20-day gavage study (Krause et al. 1976). A 3–12-week feeding
study in mice reported a NOAEL for body weight of approximately 21 mg/kg/day (Banerjee et al. 1998),
whereas a NOAEL of 100 mg/kg/day was reported for female mice in a 21-day gavage study (Chhabra et
al. 1993). The only significant finding in mice is that dose of approximately 4 mg/kg/day (only level
tested) of malathion (95% pure) given in the drinking water to Swiss mice for 15 weeks induced a 23%
decrease in body weight gain (Barlas et al. 1996). Without providing quantitative data, the investigators
indicated that the mice may have reduced their food and water intake during the study.
Administration of approximately 622 mg/kg/day of malathion (95% pure) to Osborne-Mendel rats in the
diet for 80 weeks had no significant effect on body weight (NCI 1978), but dietary doses of
approximately 332 mg/kg/day for 103 weeks reduced final body weight of male Fischer-344 rats by more
than 10% (NCI 1979a); no significant effects were seen in females. Food intake data were not provided
in the latter study. Decreased body weight gain was also reported in male and female Fischer-344 rats
administered 359 or 415 mg/kg/day, respectively, of malathion (97.1% pure) in the diet for 2 years (Daly
1996a); no significant effects were observed at 35 mg/kg/day. In the latter study, food intake was not
reduced by administration of malathion. Male and female B6C3F1 mice also showed a reduction in body
weight gain after administration of approximately 1,490 mg/kg/day of malathion (95% pure) for 80 weeks
(NCI 1978). A similar finding was reported by a Slauter (1994) in male B6C3F1 mice after dietary
administration of 1,476 mg/kg/day malathion (96.4% pure) for 18 months; in this case, the reduced
weight gain was associated with a decrease in food intake.
The significance of the reduction in body weight reported in some studies is unknown, but may reflect
decreased palatability of the food with added malathion. However, in the chronic study by Daly (1996a),
there was reduction of body weight gain in rats without a decrease in food intake. There is no evidence
from any other study suggesting that malathion decreases food utilization.