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

MALATHION 119
3. HEALTH EFFECTS
Sprague-Dawley rats in which the animals were gavaged with malathion at 0.00001–0.1 (69 mg) the LD50
dose, metabolites in urine comprised predominantly (up to 90%) dicarboxylic acid, followed by
monocarboxylic acid; alkyl phosphates were minor components (Bradway and Shafik 1977).
3.4.4.3 Dermal Exposure
A study of dermal absorption of 14 C-malathion (label position unspecified) in humans provides estimates
of kinetic parameters of malathion elimination via the urine. Fitting urinary data to a model yielded
elimination rate constants for humans, ranging from 0.094 to 0.129/hour (elimination half-time of
0.74-5.4 hours) for pure malathion and 0.079–0.130/hour (elimination half-time of 8.7–5-3 hours) for
10% aqueous malathion (Dary et al. 1994).
Studies of occupationally exposed subjects have identified and quantified several malathion metabolites
in the urine. In these cases, exposure is assumed to have been by both the inhalation and dermal routes,
but the contribution of each specific route is unknown.
In a study of date farm workers continually exposed to malathion in dusting and harvesting operations,
mid-season Monday morning prework urine samples contained low or unmeasurable levels of malathion
acids, indicating rapid metabolism and elimination (Krieger and Dinoff 2000). Estimated daily clearance
of malathion metabolites provided a measure of daily dose. Depending on the task of the crew, the
clearance ranged from 1 to 92 mg malathion equivalent/day. For loaders/applicators, the dose estimates
were 0.4–1 mg malathion equivalent/kg/day. The profile for major urinary metabolites was:
O,O-dimethylphosphorotioate (48–53%), malathion monocarboxylic acids (23–27%), and malathion
dicarboxylic acid (13–16%). These levels of "subchronic" exposure did not result in depression of either
plasma or RBC cholinesterases. Dermal doses (281 or 51 mg) of malathion self-administered on forearms
produced metabolite profiles similar to that obtained from oral dosing (Krieger and Dinoff 2000).
A study of workers and residents exposed to malathion during a spraying operation in Haiti showed
urinary malathion monocarboxylic acid at various times after the operation ranging from 0.9 to 6.8 mg/L
after the spraying week and from 0.047 to 0.13 mg/L after the weekend (Warren et al. 1985). Residents
having negligible levels of monocarboxylic acids when they returned home showed an increase to 0.084–
1.4 mg/L over the weekend. In a group of residents who were tested 1 week after the operation,
malathion monocarboxylic acids ranged from negligible to 0.31 mg/L, suggesting that malathion and/or
metabolites may be more persistent in the environment than it had been previously thought. A study of