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

MALATHION 153
3. HEALTH EFFECTS
duration oral MRL. Studies in animals provided information on lethality (NCI 1978, 1979a), systemic
effects (Desi et al. 1976; Foster 1968; Krause et al. 1976; Lox and Davis 1983; Ozmen and Akay 1993),
immunological effects (Banerjee et al. 1998; Desi et al. 1978; Rodgers and Xiong 1997c), neurological
effects (Desi et al. 1976, 1978; Fischer 1988; Husain et al. 1987; Lamb 1994b), and reproductive and
developmental effects (Balasubramanian et al. 1987a, 1987b; Kalow and Marton 1961; Krause et al.
1976; Lechner and Abdel-Rahman 1984; Ozmen and Akay 1993; Schroeder 1990). Of special interest is
a 60-day study by Lox and Davis (1983), which reported hepatocyte degeneration in rats at the very low
dose of approximately 0.15 mg/kg/day of malathion (99% pure) in drinking water (1 ppm in water). This
is one of the few studies in which malathion was administered in the drinking water. Since no liver
histopathology was described in any other intermediate-duration oral study with much higher malathion
doses either in the food or by gavage, the findings of Lox and Davis (1983) should be interpreted with
caution until such results can be replicated. Also of interest is the finding of increased peritoneal
macrophage function in mice treated for 90 days with 0.1–10 mg/kg/day by gavage (Rodgers and Xiong
1997c). However, as Rodgers and Ellefson (1992) pointed out, the physiological significance of the
magnitude of this effect is unknown. An additional 28-day immunological study in mice reported that
doses as low as 0.018 mg/kg/day of commercial-grade malathion increased the primary immune response
to immunization with SRBC (Johnson et al. 2002). Dermal data in animals were limited to information
on lethality (Dikshith et al. 1987), systemic effects (Boyes et al. 1999; Moreno 1989), and neurological
effects (Boyes et al. 1999; Dikshith et al. 1987; Moreno 1989). Results regarding systemic effects after
dermal exposure were insufficient to construct dose-response relationships, but additional studies may not
be necessary since malathion is rapidly degraded in the environment and long-term dermal exposure is
not expected to occur for the general population or for people living near waste sites.
Chronic-Duration Exposure and Cancer. Limited information was found regarding health effects
in humans after chronic-duration exposure to malathion. Information on effects of chronic exposure is
derived mostly from studies of workers in which both the inhalation and dermal routes of exposure play
significant roles. It should also be noted that although occupational exposure is generally assumed to be
chronic, for some types of occupations (i.e., pesticide applicators), exposures are usually seasonal,
involving only a few weeks or months per year. A study of workers exposed to organophosphates (not
only malathion) for up to 29 years found a higher frequency of respiratory tract infections among the
workers than in controls (Hermanowicz and Kossman 1984). The authors also observed marked
impairments of neutrophil chemotaxis and significantly decreased neutrophil adhesion among the
workers. A study at a pesticide manufacturer (primarily malathion) found an inverse relationship between
hemoglobin concentration and duration of employment (Singaravelu et al. 1998). Studies of workers