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

MALATHION 34
3. HEALTH EFFECTS
Studies in which workers were exposed to a combination of pesticides (not limited to organophosphates)
that included malathion showed either a decrease of 26% in RBC cholinesterase in 85 workers exposed
from 0.1 to 29 years compared with the same number of unexposed individuals (Hermanowicz and
Kossman 1984) or no significant difference among 11 pesticide applicators when comparing exposure
periods with periods during the year of no exposure (StDlberg et al. 1978). Among four studies that
measured changes in plasma cholinesterase, levels were 8–53% lower in groups of pesticide applicators
when compared with controls (Ernest et al. 1995; Hermanowicz and Kossman 1984; Peedicayil et al.
1991) or with periods of no exposure (StDlberg et al. 1978). Numbers of exposed individuals evaluated in
these four studies ranged from 11 to 85 pesticide workers.
Some studies also examined the possible association between changes in cholinesterase levels and the
presence or absence of clinical signs of cholinergic stimulation. For example, Peedicayil et al. (1991)
found that plasma cholinesterase activity in workers who exhibited cholinergic symptoms and signs was
17% lower than in workers without symptoms and signs. Similar findings were reported by Ernest et al.
(1995). No cholinergic signs were seen in the StDlberg et al. (1978) study in which the activities of RBC
and plasma cholinesterase varied less than 10% between pre- and postexposure.
Neurophysiological Effects. A significantly higher percentage of peripheral neuropathies (evaluated by
electromyograph [EMG] recordings) were observed among pesticide workers than in controls in a study
by Ernest et al. (1995). Those who had clinical features of peripheral neuropathy had been exposed to
organophosphates from 4 to 10 years. A similar finding was reported by Peedicayil et al. (1991),
although the specific method to assess peripheral neuropathy was not indicated. Only a slight reduction
(3%) in sensory nerve conduction velocity was seen among a group of 11 workers exposed to
organophosphates for periods ranging from 1 to 24 years (StDlberg et al. 1978); however, there were no
significant alterations in motor nerve conduction velocity or any indication of altered synaptic
transmission. No evidence of neuromuscular insufficiency was reported by Jušić et al. (1980) among a
group of 14 workers exposed to a pesticide formulation containing 57% malathion 4–5 hours/day, 4–
6 months during the year.
The study by Kahn et al. (1992) described above (Respiratory Effects) on residents from an urban area
where aerial spraying with malathion was conducted did not find a significant increase in visits to hospital
emergency departments for the category, anxiety, following the spraying. In fact, after the spraying, there
was a decrease in anxiety-related symptoms. The study also found no increase in self-reported symptoms
that would indicate effects consistent with organophosphate poisoning.