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

MALATHION 111
3. HEALTH EFFECTS
liver, kidney, lungs, heart, brain, spleen, and muscles. The highest concentration of malathion was found
in the kidneys (294–614 µg/g), whereas the muscles had the least (8–40 µg/g).
Plasma 14 C level was measured in rats over 48 hours following gavage of a dose of 10 mg/kg of ethyl
14 14
C-malathion or in combination with 10 mg/kg carbaryl (Lechner and Abdel-Rahman 1986). The C
levels of malathion alone and in combination with carbaryl reached a peak in plasma of 12.5 and
19.9 µg/mL 1 hour after dosing, and the absorption half-times were 1.82 and 1.91 hours, respectively.
The α-phase half-lives of elimination were 18.5 and 14.5 hours and those for the β-phase were 7.16 and
10.6 hours, for malathion alone and in combination with carbaryl, respectively.
In an autoradiographic study, a single gavage dose of 3 mg/kg of methoxy 14 C-malathion in corn oil was
administered to male Sprague-Dawley rats (Saleh et al. 1997). Rats were frozen in dry ice/hexane after
4 hours and sectioned for whole-body autoradiography. About 75% of the radioactivity electronically
recorded in sagittal sections was in the stomach and 18% was in the small intestine; 7% was excreted in
saliva. The authors concluded that a very small percentage of the dose was absorbed. This unusual
finding could be partly related to the relatively large amount of the vehicle used (1 mL of corn oil to small
nonfasted rats, weighing 80–120 g), and needs confirmatory work.
Garcia-Repetto et al. (1995) analyzed the distribution of a single dose of malathion administered by
gavage to male albino rats at the rate of 467 mg/kg by using olive oil as a vehicle (20 mg/mL). Rats were
sacrificed under ether anesthesia and tissues were obtained. Malathion was extracted from tissues and
quantified by gas chromatography. Data were reported for days 4, 8, 12, 16, 20, and 30. Malathion was
detected in blood only on day 4 (3.58 µg/g). Malathion in adipose tissue was highest on day 4 (2.63 µg/g)
and declined through day 12. Muscle showed 4.24 µg/g on day 4 and decreasing levels through day 16.
In the liver, malathion increased to day 16 (1.13 µg/g) and declined to day 20. The brain level reached
the peak on day 16 (0.88 µg/g). No malathion was detected on day 30.
Transfer of malathion and/or metabolites to the fetus across the placenta was demonstrated in a study in
rabbits (Machin and McBride 1989b). Gavage doses of 126 mg malathion/kg/day administered to the
pregnant animals on gestation days 28 through 30 resulted in decreases between 54 and 79% in fetal
plasma cholinesterase activity and between 60 and 66% in fetal brain cholinesterase 1 hour after the last
dose.