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

MALATHION 132
3. HEALTH EFFECTS
In recent years, concern has been raised that many pesticides and industrial chemicals are endocrineactive
compounds capable of having widespread effects on humans and wildlife (Crisp et al. 1998; Daston
et al. 1997; Safe et al. 1997). Particular attention has been paid to the possibility of these compounds
mimicking or antagonizing the action of estrogen, and more recently, their potential anti-androgenic
properties. Estrogen influences the growth, differentiation, and functioning of many target tissues,
including female and male reproductive systems, such as mammary gland, uterus, vagina, ovary, testes,
epididymis, and prostate. Thus far, there is no evidence that malathion is an endocrine disruptor in
humans at the levels found in the environment.
A study following malathion spraying in the San Francisco Bay area found an increase in some anomalies
at birth, but those that occurred most frequently than expected did not represent a biologically consistent
pattern (Grether et al. 1987). A similar study of women who were pregnant during periods of malathion
spraying to control an infestation by the Mediterranean fruit fly found no significant association between
exposure to malathion and the incidence of spontaneous abortions, but there was a weak association
between stillbirths and exposure accumulated up to 1 month before death as well as an increased
incidence of gastrointestinal anomalies (Thomas et al. 1992). Exposure misclassification may have
precluded drawing any firm conclusions in this report. An additional study of male workers exposed to
malathion and several pesticides, including organochlorine pesticides, found decreased fertility among the
workers, a higher percent of abortions and stillbirths among the wives of exposed males, and congenital
defects in their offspring (Rupa et al. 1991b). The role of malathion, if any, cannot be determined. A
case report described by Lindhout and Hageman (1987) discussed the possible association between
dermal exposure of a pregnant women to a hair lotion containing malathion and the birth of a severely
malformed child, but a causal link is difficult to establish. Decreased serum levels of ACTH, cortisol, and
prolactin were reported in patients with severe intoxication following intentional ingestion of unspecified
amounts of malathion (Güven et al. 1999). Transient alterations in thyroid hormones and TSH were also
seen. The toxicological significance of these findings is unknown.
Increased pituitary gland weight and serum prolactin levels and decreased pituitary levels of prolactin
were reported in male Wistar rats administered approximately 225 mg/kg/day of malathion for 6 days
(Simionescu et al. 1977). An intermediate-duration study found congestion in the zona reticularis of the
adrenal glands from rats treated by gavage with 10 mg/kg/day of malathion (94% pure) for 15 weeks
(Ozmen and Akay 1993). Serum cortisol and aldosterone levels were increased at 10 mg/kg/day, but not
at 100 mg/kg/day. Serum T4, T3, testosterone, and 17β-estradiol levels were not significantly affected by