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

MALATHION 98
3. HEALTH EFFECTS
dermal toxicity of a malathion formulation commonly used to treat house pets. A dog was sprayed over
the entire body with a solution containing 0.5% malathion 3 times in a week and was observed for up to
41 days following the treatment; plasma and RBC cholinesterase were also determined. No clinical signs
of toxicity were observed during the study, but both plasma and RBC cholinesterase activities were
inhibited by application of malathion. A maximum inhibition of 36% of the plasma cholinesterase
activity and 34% of the RBC activity occurred the day of the second treatment, but by day 19, enzyme
activities had recovered to pretreatment values. No doses could be estimated from these two studies.
Repeated dermal doses of 200 mg/kg/day of malathion (98% pure) in acetone, which were lethal to
guinea pigs, inhibited brain and RBC cholinesterase activity by 45–52% after 30 days of treatment, but
did not induce gross or microscopical alterations in the brain (Dikshith et al. 1987). The animals that died
showed frank signs of cholinergic stimulation before dying. A 65%, inhibition of cerebrum
cholinesterase activity was reported in male New Zealand rabbits applied malathion (94% pure) on the
skin for 6 hours/day, 5 days/week for 3 weeks (Moreno 1989). Doses of 300 mg/kg/day decreased RBC
cholinesterase activity by 26% in females, whereas the lowest dose level tested, 50 mg/kg/day, caused no
significant inhibition of plasma, RBC, cerebrum, or cerebellum cholinesterase activities (Moreno 1989).
No signs of toxicity were observed in this study.
In the Boyes et al. (1999) study that was briefly described under Ocular Effects, the authors also
examined the effects of malathion on visual evoked potentials (VEP) in Long-Evans rats by implanting
the animals with cranial electrodes for recording of VEP. The amount of malathion applied to the eye
resulted in approximate doses of 500 mg/kg/day for 4 weeks. Treatment with malathion had no
significant effect on the amplitude or phase, or the first harmonic of the VEPs. During the study, there
were no signs of cholinergic activation. Examination of the retina and optic nerve 42 days after
termination of the study revealed no treatment-related alterations.
The highest NOAEL values and all reliable LOAEL values for neurological effects in each species and
duration category are recorded in Table 3-3.
3.2.3.5 Reproductive Effects
No studies were located regarding reproductive effects in humans following dermal exposure to
malathion. A study in male guinea pigs reported a decrease in absolute testes weight following
application of 400 mg/kg/day of malathion (98% pure) in acetone to the skin for 30 days; however, doses