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

MALATHION 118
3.4.4.1 Inhalation Exposure
3. HEALTH EFFECTS
No information was located regarding elimination of malathion following inhalation exposure. However,
in the studies of occupational exposures discussed in Section 3.4.4.3 below, workers were most likely
exposed by both the inhalation and dermal routes, but the contribution of each route is difficult to
establish.
3.4.4.2 Oral Exposure
In a study by Krieger and Dinoff (2000), malathion metabolites were analyzed in the urine of a volunteer
who ingested single doses of 7.7 or 15.6 mg of malathion in gelatin capsules. Monocarboxylic acids were
more abundant than dicarboxylic acid, and dimethyl phosphorothioic acid was the main alkylphosphate
metabolite; more than 95% was recovered in urine. In an earlier study of a subject who ingested a high
amount of malathion (200 mL of 50% malathion), analysis of the second 24-hour urine sample also
showed monocarboxylic acids as the major metabolites followed by dimethyl phosphorothioic acid
(Bradway and Shafik 1977). An estimated half-life of 6.2 hours for the fast phase of elimination was
reported for a 43-year-old woman who ingested malathion (Vasilic et al. 1999).
In animals, elimination of ingested malathion occurs rapidly mainly via the kidney. For instance, male
Holtzman rats eliminated 91.7% of radioactivity of a dose of 25 mg of 14 C-ethyl malathion within
24 hours (83.4% in urine, 5.51% in feces, and 2.77% as CO2); 7.75% remained in the gastrointestinal
contents (Bourke et al. 1968). Urinary excretion at 8 hours was 44.1% of the administered dose.
Similarly, in a study of pesticide combination on toxicokinetics, 10 mg/kg 14 C-ethyl malathion given to
fasted female Sprague-Dawley rats by gavage in 0.25 mL corn oil was excreted rapidly in the urine, 68%
in 8 hours and 93% in 24 hours (Lechner and Abdel-Rahman 1986). A thin layer chromatography (TLC)
analysis of chloroform extracts from acidified 24-hour urine provided a urinary metabolite profile:
malathion 0.01%, malaoxon 1.44%, malathion monoacid 0.42%, and malathion diacid 0.06% of the dose.
Carbaryl coadministered at 10 mg/kg altered the profile and raised malaoxon to 7.5% and malathion
dicarboxylic acid to 1.48%. No additional confirmation of identity of malaoxon was reported.
In a study in male Sprague-Dawley rats, about 90% of 14 C-methoxy malathion (280 mg/kg by gavage)
was excreted into urine within 24 hours of ingestion (Abou Zeid et al. 1993). In another study in male