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

MALATHION 152
3. HEALTH EFFECTS
Parker and Chattin (1955) also described a case of a 10-year-old girl who had neurological manifestations
of poisoning after having extensive dermal contact with a malathion formulation in the form of flakes.
Also, laboratory studies in volunteers showed that a single exposure to 10% malathion (95% pure)
induced contact sensitization in almost half of the subjects, and that 0.1 and 0.01% concentrations of
99.3% malathion were able to evoke positive responses in previously sensitized individuals (Milby and
Epstein 1964). Information on effects of malathion after acute dermal exposure in animals was limited a
study of lethality in rats (Gaines 1960), a study of delayed-type hypersensitivity in mice (Cushman and
Street 1983), and a report on subtle immunological alterations in rats and mice following a single dermal
application of malathion (Rodgers and Xiong 1997c). Qualitative data (no dose level) on RBC and
plasma cholinesterase were also available from a study in dogs (Vestweber and Kruckenberg 1972).
Although the information available does not suggest that the toxicity of malathion is route-dependent,
further well-conducted acute dermal studies seem necessary to establish dose-response relationships for a
range of end points. This is important because considerable dermal exposure to malathion can occur for
the residential handler and during post-application events. Furthermore, under certain exposure scenarios
such as following aerial application of malathion over urban areas, dermal doses may be orders of
magnitude higher than inhalation doses (Marty et al. 1994).
Intermediate-Duration Exposure. Few intermediate-duration studies were located that described
health effects in humans specifically exposed to malathion. However, it is reasonable to assume that
many of the studies on cohorts exposed occupationally to malathion, or to pesticides in general, described
in Section 3.2, included subjects who may have been exposed for intermediate durations. Limited
information is available from a controlled inhalation study in volunteers that identified a NOAEL of
85 mg/m 3 for body weight and neurological effects (cholinesterase activity) (Golz 1959); subjects were
exposed to malathion aerosols 2 hours/day for 42 days. Limited data were also located in the studies
available regarding effects in animals exposed to malathion in the air. A 13-week study in rats reported
hyperplastic changes in the epithelium from the upper respiratory tract following intermittent exposure to
100 mg/m 3 of malathion aerosol and significant reduction in RBC cholinesterase activity at 450 mg/m 3
and higher (Beattie 1994). The LOAEL of 100 mg/m 3 was used to derive an intermediate inhalation
MRL for malathion.
A study in humans administered malathion in capsules for up to 56 days identified a NOAEL of
0.34 mg/kg/day for hematological and renal effects; this dose level also constituted a LOAEL for
neurological effects (plasma and RBC cholinesterase activity) (Moeller and Rider 1962). The NOAEL
for neurological effects was 0.23 mg/kg/day and was used as the basis for derivation of an intermediate-