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

MALATHION 161
3. HEALTH EFFECTS
Epidemiological and Human Dosimetry Studies. Information on the health effects of malathion
in humans is derived from case reports of accidental or intentional exposure to malathion (Choi et al.
1998; Crowley and Johns 1966; Dive et al. 1994; Faragó 1967; Jušić and Milić 1978; Monje Argiles et al.
1990; Morgade and Barquet 1982; Namba et al. 1970; Ramu et al. 1973; Tuthill 1958; Zivot et al. 1993),
epidemiological studies (Grether et al. 1987; Kahn et al. 1992; Thomas et al. 1992), studies of exposure to
multiple pesticides including malathion (Brown et al. 1990, 1993; Cantor et al. 1992; Ernest et al. 1995;
Hermanowicz and Kossman 1984; Peedicayil et al. 1991; Rupa et al. 1991b; Stålberg et al. 1978; Zahm
1997; Zahm et al. 1993), and controlled exposure studies (Golz 1959; Milby and Epstein 1964; Moeller
and Rider 1962). The most likely identifiable subpopulations exposed to malathion are pesticide
applicators, farm workers, individuals involved in the production of malathion, and individuals exposed
in homes after residential application. Well-designed epidemiological studies of exposed workers and
follow-up evaluations of cohorts from the general population who may have been exposed during aerial
application of the pesticide are needed. Specific assessment of cancer risks and examination of the effects
of malathion on the nervous system and immune systems are needed. The nervous system is a known
target of acute exposure, but little is known on possible long-term effects of acute exposure. Malathion
seems to have modulatory effects on the immune system of animals at noncholinergic dose levels.
Therefore, evaluation of the immune status of exposed humans would be important. Studies in animals
have shown that impurities in malathion formulations play an important role in the toxicity of malathion
and have inherent toxicity themselves. Identification of impurities and inert ingredients in commercial
formulations as well as potential levels of exposure seems indicated.
Biomarkers of Exposure and Effect.
Exposure. Malathion metabolites (MCA, DCA, DMPT, DMPDT) have been measured in the urine from
the general U.S. population and from workers exposed to the pesticide (Fenske 1988; Krieger and Dinoff
2000; Kutz et al. 1992; MacIntosh et al. 1999b; Warren et al. 1985). In the general population, MCA was
the most abundant and was found in only a small percentage of the samples (Kutz et al. 1992; MacIntosh
et al. 1999b). Since malathion does not seem to accumulate in the body, the presence of malathion
metabolites in the general population probably reflects continuous background exposure via the food
rather than isolated exposures to significant amounts. Additional studies of the general population
correlating malathion metabolite levels with health status as well as with dietary habits would provide
useful information for risk characterization and risk assessment.
Suggestive evidence of malathion-induced specific mutations in human T-lymphocytes exposed in vitro
was presented by Pluth et al. (1996, 1998). Further studies on this issue are needed to establish dose-