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

MALATHION 65
3. HEALTH EFFECTS
effects were observed in mice from the low-dose group administered approximately 1,490 mg
malathion/kg/day. Another long-term study (18 months) in mice reported an increased incidence of
nonneoplastic nasal lesions in female B6C3F1 mice treated with 96.4% pure malathion in the diet at
167 mg/kg/day and in males and females at approximately 1,500 mg/kg/day (Slauter 1994). These
lesions were characterized as exudate, suppurative, increased glandular secretion, olfactory atrophy, and
olfactory respiratory metaplasia. No such lesions were seen in animals treated with about 20 mg/kg/day
of malathion or less.
Cardiovascular Effects. Cardiovascular effects were observed in almost all reported cases of
malathion poisoning (Crowley and Johns 1966; Dive et al. 1994; Healy 1959; Jušić and Milić 1978;
Monje Argiles et al. 1990; Namba et al. 1970; Rivett and Potgieter 1987; Zivot et al. 1993). In general,
signs and symptoms on admission included bradycardia and low blood pressure as expected from vagal
stimulation. Several cases also observed atrio-ventricular conduction disturbances within a few days after
ingestion of the pesticide (Crawley and Johns 1966; Dive et al. 1994; Monje Argiles et al. 1990). Doses
estimated in these cases ranged from 214 to 2,117 mg/kg. In contrast, Choi et al. (1998) reported a
normal electrocardiogram and chest x-ray performed in the emergency room in a woman who ingested
approximately 1,071 mg/kg malathion.
Tachycardia was reported in many Wistar rats treated with about 593 mg/kg/day of malathion
(unspecified purity) in the diet for 7 days, but not in those treated with ≤411 mg/kg/day malathion (Ojha
et al. 1992). Tachycardia may be the result of cholinergic stimulation of parasympathetic and
sympathetic autonomic ganglia. Administration of gavage doses of 390 mg malathion/kg/day
(unspecified purity) for 1–2 weeks to rats caused focal hemorrhage in the heart (Piramanayagam and
Manohar 2002). A single gavage dose of 1,950 mg/kg of malathion (95% pure), the only dose level
tested, caused congestion and hemorrhage in the hearts of male Wistar rats 2 days after dosing, females
were not tested (Piramanayagam et al. 1996). Although the authors did not specifically mention the heart,
they stated that by day 12 after dosing, almost all organs examined appeared normal.
No adverse cardiovascular effects were reported in long-term dietary studies in rats (up to 622 mg
malathion/kg/day) (NCI 1978, 1979a) and mice (up to 2,980 mg malathion/kg/day) (NCI 1978; Slauter
1994).
Gastrointestinal Effects. Abdominal cramping, diarrhea, nausea, and vomiting were common signs
and symptoms observed following ingestion malathion in some of the reports available (Amos and Hall