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

MALATHION 39
3. HEALTH EFFECTS
Risks for rectal cancer were elevated in women and men combined (SIR=2.94, CI=1.07–6.40) and were
even higher in a subgroup of licensed pesticide applicators who used pesticides for agricultural purposes
(SIR=4.63, CI=1.49–10.80) in the study by Zhong and Rafnsson (1996). Finally, a study in Los Angeles
County, California, involving mothers of 224 cases and 218 controls, who used (from pregnancy to
diagnosis) household pesticides for a number of domestic purposes, found no elevated risks in pediatric
brain tumors among the user group (Pogoda and Preston-Martin 1997).
No studies were located regarding cancer in animals following inhalation exposure to malathion.
3.2.2 Oral Exposure
The human data in this section are derived primarily from case reports in which the actual doses ingested
are unknown. However, many cases provide enough information (i.e., volume of the formulation taken
and percent malathion in the formulation) to at least make reasonable estimates. One additional factor to
consider is that malathion formulations also contain many other chemicals, such as solvents and
impurities, which may form during long periods of storage. Many impurities greatly increase the toxicity
of malathion formulations relative to pure malathion. Therefore, caution should be exercised when
comparing oral doses estimated from human cases with doses used in experiments in laboratory animals.
3.2.2.1 Death
Perhaps because of its widespread use and availability, many cases of fatal ingestion of malathion in
humans (suicides and poisonings) have been documented in the literature (Faragó 1967; Jušić and Milić
1978; Morgade and Barquet 1982; Namba et al. 1970; Zivot et al. 1993). For example, Faragó (1967)
described four cases of lethal intentional ingestion of a formulation containing 35% malathion, and based
on the amount ingested, the lethal doses can be estimated to have been between 350 and 1,000 mg/kg. No
dose can be estimated in a case described by Zivot et al. (1993), but the antemortem blood level of
malathion in the patient on admission was 23.9 mg/L. A dose between 857 and 1,286 mg/kg can be
estimated to have been ingested in a case described by Namba et al. (1970) and 2,000 mg/kg in one
described by Jušić and Milić (1978). Talcott et al. (1979a) estimated a median lethal dose for malathion
in humans of 3,655 mg/kg by using an equation relating carboxylesterase (serum and liver) and toxicity.
The equation was experimentally constructed from data obtained in mice treated with various doses of
malathion and carboxylesterase inhibitors. The higher estimate of Talcott et al. (1979a) probably reflects