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

MALATHION 66
3. HEALTH EFFECTS
1965; Crowley and Johns 1966; Healy 1959; Rivett and Potgieter 1987). These effects result from the
stimulation of parasympathetic autonomic postganglionic nerves by organophosphates and the lack of
reporting of these effects in the additional studies reviewed most likely reflects incomplete reporting
rather than the absence of gastrointestinal effects.
Diarrhea was observed in beagle dogs treated with 125 mg/kg/day (the lowest dose tested) malathion
(92.4% pure) in gelatin capsules for 28 days (Fischer 1988). Rats administered malathion (22 mg/kg/day)
by gavage in a mixture of alcohol and water for 6 days suffered diarrhea (Simionescu et al. 1977).
Diarrhea is a common muscarinic sign of organophosphate pesticide intoxication. Rats treated with
gavage doses of 130 mg/kg/day of malathion (unspecified purity) for 1–2 weeks showed gastrointestinal
alterations described by the authors as catarrhal changes (Piramanayagam and Manohar 2002).
Information from a single dose study in rats suggested that malathion may alter gastrointestinal
absorption. Absorption was examined in an isolated portion of the intestines from male Wistar rats
48 hours after administration of a single gavage dose of 1,000 mg/kg/day of technical malathion (purity
unspecified) (Chowdhury et al. 1980). Absorption of glucose and glycine were reduced and the activities
of some brush border enzymes were depressed in the malathion-treated rats. In a subsequent study from
the same group in which rats were treated for 45 days with 50 mg/kg/day malathion, the authors found
that treatment with malathion significantly increased the absorption of glucose, phenylalanine, and lysine,
but not glycine, and increased brush border enzyme activities (Wali et al. 1984).
No gastrointestinal effects were reported in Osborne-Mendel rats administered up to approximately
622 mg/kg/day malathion (95% pure) in the diet for 80 weeks or in B6C3F1 mice treated with up to
2,980 mg/kg/day in the diet for 80 weeks (NCI 1978). However, male Fischer-344 rats administered
166 mg/kg/day malathion (95% pure) or more in the diet for 103 weeks developed chronic inflammation
of the stomach and stomach ulcers.
Hematological Effects. Almost all of the case reports of oral ingestion of malathion described the
results of laboratory tests conducted on the patients on or following admission to treatment centers. In
most cases, these included complete and differential blood counts, which may or may have not deviated
from the normal ranges. However, observed deviations are probably not unique to malathion
intoxication, or to organophosphates in general, but represent stress reactions (Aaron and Howland 1998).
For example, it is not uncommon to find high hematocrit secondary to hemoconcentration due to large
fluid losses (Aaron and Howland 1998). Therefore, a detailed discussion of specific alterations from the
individual cases is of little utility.