What are the toxic effects for humans of malathion?

Question

What are the toxic effects for humans of malathion?

Answer 1

Malathion itself is not toxic; however, absorption or ingestion into the human body readily results in its metabolism to malaoxon, which is toxic in high amounts. Chronic exposure to low levels of malathion have been hypothesized to impair memory, but this is disputed. There is currently no reliable information on adverse health effects of chronic exposure to malathion.[8] Acute exposure to extremely high levels of malathion will cause body-wide symptoms whose intensity will be dependent on the severity of exposure. Possible symptoms include skin and eye irritation, cramps, nausea, diarrhea, excessive sweating, seizures and even death. Most symptoms tend to resolve within several weeks. Malathion present in untreated water is converted to malaoxon during the chlorination phase of water treatment, so malathion should not be used in waters that may be used as a source for drinking water, or any upstream waters.

In 1976, numerous malaria workers in Pakistan were poisoned by isomalathion, a contaminant that may be present in some preparations of malathion. [9] It is capable of inhibiting carboxyesterase enzymes in those exposed to it. It was discovered that poor work practices had resulted in excessive direct skin contact with isomalathion contained in the malathion solutions. Implementation of good work practices, and the cessation of use of malathion contaminated with isomalathion led to the cessation of poisoning cases.

[edit] Carcinogenicity

Malathion is classified by US EPA as having “suggestive evidence of carcinogenicity but not sufficient to assess human carcinogenic potential.”[10] This rating implies that insufficient evidence is available to either rule out malathion as a carcinogen, or to state that it is a carcinogen. No studies on carcinogenicity have been performed in humans; however, studies in rats and mice have yeilded conflicting results. Liver tumours were found to be induced in rats, but only at excessive doses. On the other hand, malaoxon, a structurally related chemical, was found not induce tumour formation in rats. A review of the classification of malathion as 'suggestive' was carried out in 2000, by the FIFRA Scientific Advisory Panel. The conclusion of this panel was that there was still insufficient evidence to either declare malathion as non-carcinogenic, or to declare it a carcinogen.