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

MALATHION 95
3. HEALTH EFFECTS
North Carolina to evaluate the relationship between retinal degeneration and pesticide application. They
compared pesticide use in 154 applicators with the disease and 17,804 applicators with no retinal
degeneration. Organophosphate use was significantly associated with retinal degeneration only in North
Carolina, but not in Iowa or both states together, nor in various subgroups, and no dose-response was
observed. Kamel et al. (2000) suggested that because nearly all applicators (both cases and controls)
evaluated in their study used organophosphate insecticides, exposures could not be effectively evaluated.
At the same time, they pointed out that it would be premature to conclude that no risk existed. Anecdotal
information was found in a study of self-reported symptoms in 22 seamen who may have been exposed to
a single cloud of malathion that escaped from a nearby overheated tank (Markowitz et al. 1986).
Compared with a group of controls, the seamen reported significantly more problems associated with
swelling or irritation, blurring, double vision, or poor vision when contacted 12 days following the
incident. It should be noted that there was no evidence of actual exposure to the chemical; therefore, the
role of malathion, if any, cannot be determined.
Transient conjunctivitis was observed in mice following a brief whole-body submersion in a dip
preparation containing 2 or 8% malathion (Relford et al. 1989). A recent study by Boyes et al. (1999)
examined the ocular toxicity of malathion in Long-Evans rats. Malathion alone or with insect bait was
applied directly to the eyes at a level of 100 mg per eye, 5 days/week for 4 weeks. Assuming a body
weight of about 0.4 kg for a 60-day-old Long-Evans rat, the daily dose can be estimated at
500 mg/kg/day. Approximately 38 days after completion of the study, the eyes were examined by an
ophthalmologist. Application of malathion caused only slight signs of ocular irritation described as mild
redness of the periocular tissue. The ophthalmologic examination did not reveal any significant changes
in the anterior or posterior segment of the eye. Boyes et al. (1999) pointed out that while there was no
apparent damage, the possibility cannot be ruled out that acute alterations detectable shortly after dosing
could have resolved during the 38–42-day posttreatment period. They also estimated that the amount of
malathion applied would yield a dose of 2,000 µg of malathion per mm 2 , which is about 84,000 times
greater than what would be expected from an aerial application of the pesticide.
Body Weight Effects. No information was located regarding body weight effects in humans
following dermal exposure to malathion. No significant effects on body weight were reported in rats
treated topically in the eye with approximately 500 mg/kg/day of malathion for 4 weeks (Boyes et al.
1999). No significant effect on body weight was observed in rabbits treated dermally with up to
1,000 mg/kg/day malathion (94% pure) for 3 weeks (Moreno 1989).