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

MALATHION 158
3. HEALTH EFFECTS
who discussed a possible association between the use of a hair lotion containing malathion by a woman
during weeks 11 and 12 of pregnancy and the birth of a severely malformed child. However, a causal link
is difficult to establish.
No information was located regarding developmental effects in animals following inhalation or dermal
exposure to malathion. Transfer of malathion (and/or metabolites) to the fetus through the placenta and
via maternal milk has been demonstrated indirectly (Chhabra et al. 1993; Mathews and Devi 1994). Oral
studies in rats and rabbits have not shown embryotoxicity (Khera et al. 1978; Lochry 1989; Machin and
McBride 1989a; Siglin 1985) or showed embryotoxicity at doses that also caused maternal toxicity
(Prabhakaran et al. 1993). However, reduced fetal weight and crown-rump length were seen in mice in a
study that provided no information on maternal effects (Asmatullah et al. 1993). A study by Kalow and
Martin (1961) found increased neonatal mortality in rats treated for at least 5 months before pregnancy,
but again, no information was presented on maternal effects, which seriously weakens the evidence. In a
2-generation study, the only developmental effect noticed was a decrease in body weight gain in pups
from the F1A and F2B litters during the lactation period at parental doses of 394 mg/kg/day of malathion
for males and 451 mg/kg/day for females, with corresponding NOAELs of 131 and 153 mg/kg/day
(Schroeder 1990). No teratogenic effects of malathion were reported in the studies evaluated (Khera et al.
1978; Lechner and Abdel-Rahman 1984; Lochry 1989; Prabhakaran et al. 1993; Schroeder 1990; Siglin
1985). Although most of the data suggest that malathion is not a developmental toxicant, there is still
uncertainty regarding whether effects could occur at doses not causing maternal toxicity, largely because
of limitations of experimental design or reporting in some studies. Therefore, a well-designed study is
warranted. In addition, a developmental neurotoxicity study in rats in which pups are tested at various
ages after being exposed in utero and/or via maternal milk would fill a data gap. The oral route should be
preferred to complement the existing information and because there is no evidence that the toxicity of
malathion is route-specific.
Immunotoxicity. There is some information suggesting that exposure to malathion may affect the
immune system in humans. Albright et al. (1983) described a case of possible immune complex
nephropathy in a man who developed transient renal insufficiency with massive proteinuria after spraying
intensively with malathion. Impairment of neutrophil chemotaxis was observed among a group of
workers exposed to organophosphate pesticides, including malathion, for 0.1–29 years (Hermanowicz and
Kossman 1984). Malathion was shown to be a contact sensitizer in a laboratory study with volunteers
(Milby and Epstein 1964). A case of immediate IgE reaction to malathion and another of irritant reaction
to malathion and to the bait was described among subjects who developed dermatitis following aerial