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

MALATHION 67
3. HEALTH EFFECTS
Moeller and Rider (1962) conducted a controlled study in which male volunteers were administered daily
capsules containing malathion (purity not reported) in corn oil that provided an approximate dose of
0.11 mg malathion/kg/day for 32 days, 0.23 mg malathion/kg/day for 47 days, or 0.34 mg
malathion/kg/day for 56 days. Routine blood counts conducted at the end of each study period did not
detect any significant changes.
Few reports were available that provided some information on hematological effects in animals following
oral exposure to malathion. A study reported no hematological effects in pregnant Sprague-Dawley rats
administered the relatively low dose of 0.73 mg/kg/day of malathion (analytical grade) bound to wheat
during gestation days (Gd) 5–11 (Bitsi et al. 1994). Lox (1983) observed a decrease in hematocrit and in
platelet counts in rats 2 hours after being gavaged once with a suspension of malathion (99% pure) in
water; no other dose level was tested. Treatment of Sprague-Dawley rats with approximately
89 mg/kg/day malathion in the drinking water for 14 days resulted in a significant increase in fibrinogen
and decrease in clotting factor XII, whereas a high dose of about 111 mg/kg/day decreased clotting factor
II and XII and increased factor X (Lox 1985). A much smaller dose of approximately 0.15 mg/kg/day of
malathion (99% pure), also in drinking water, for 6 months significantly prolonged prothrombin and
partial thromboplastin times in female Sprague-Dawley rats, but had no significant effect on fibrinogen or
coagulation factors II, VII, or X (Lox and Davis 1983); this treatment caused no significant alterations on
hematocrit or platelet counts. A 90-day-duration study found no significant effect of malathion
(95% pure) on blood counts (differential or quantitative) following administration in the diet at a level of
75 mg/kg/day (Desi et al. 1976). A 2-year-duration study in Fischer-344 rats observed a decrease in
hemoglobin, hematocrit, mean corpuscular volume, and mean cell hemoglobin in males and females
following dosing of 6,000 ppm malathion (97.1% pure) in the diet (359 mg/kg/day for males,
415 mg/kg/day for females) (Daly 1996a).
Musculoskeletal Effects. No studies were located regarding musculoskeletal effects in humans
following oral exposure to malathion. The only information available regarding musculoskeletal effects
of malathion in animals is that from chronic studies. These studies reported no gross or microscopic
alterations in bone (unspecified) from Osborne-Mendel rats treated with up to 622 mg/kg/day of
malathion (95% pure) for 80 weeks (NCI 1978), in Fischer-344 rats given up to 332 mg/kg/day for
103 weeks (NCI 1979a), or in B6C3F1 mice administered up to 2,980 mg/kg/day malathion for 80 weeks
(NCI 1978).