Malathion - what is it?

and genetic health studies 

The following is quoted directly from the "Introduction" in the article "Increased Frequency of Specific Genomic Deletions Resulting from Malathion Exposure." The article was written by researchers at the Genetics Laboratory, University of Vermont. 
Dr.. Janice Pluth, Janie Nicklas, Patrick O'Neill, Richard Albertini, Ph.(802) 656-8856 

"Malathion, 0,0-dimethyl-S-(1,2-dicarbethoxyethyl) dithiophosphate, an organophosphorus pesticide, is widely used for both domestic and commercial agricultural purposes. It is considered to be one of the safest organophosphate insecticides, and has been used in large pest eradication programs in Florida, Texas, and California. Technical-grade malathion (the grade usually used for agricultural purposes) is usually 90-95% pure and may contain up to 11 impurities formed during its production and/or storage. Some of these impurities have been found to be significantly more toxic than malathion or to potentiate the toxicity of malathion.  

Malathion has been widely studied in a variety of systems, but there is still some controversy over malathion's mutagenic and/or genotoxic potential for humans. No mutagenic effect has been shown in the majority of studies using bacteria and yeast . However, two gene mutation studies using a mammalian system, the mouse lymphoma thymidine kinase assay, and the active metabolite, malaoxon, did give positive results (1,2). Researchers Degraeve and Moutschen found no increase in chromosome aberrations in studies using the mouse bone marrow cells, spermatogonia, and primary spermatocytes after either oral or injection, whereas a large number of studies using human cells have shown a significant increase in chromosome aberrations and/or sister chromatid exchanges with exposure to malathion (3-7). There has also been some evidence of malathion having a teratogenic effect (the ability to cause birth defects): the offspring of rats fed with 240 mg/kg/day (milligrams per kilogram of body weight per day) malathion exhibited growth retardation and elevated mortality, although no negative effects were observed in the parents (8). 

Many in vivo (live) studies in which individuals were exposed to malathion and/or other pesticides have shown a genotoxic effect (genotoxic means the ability to damage the genes on the DNA molecule - our genes control every aspect of our living self - approximately 200 genes have been located which control immune system function and 200 genes control liver function). 

Yoder found a 5-fold increase in chromatid breaks in farmers during the summer season, when pesticide usage was highest (9). Van Baa studied individuals who had been exposed only to acute doses of malathion (acute means a single large dose) and found a significant increase in the percentage of stable and unstable chromosome aberrations both immediately after exposure and 1 month later. Lipowitz showed that exposure to environmental pesticides (one of which was malathion) resulted in a 10-20 fold increased incidence of a particular cytogenetic aberration in a population of agricultural workers. Although this aberration itself is not oncogenic (cancer causing), these researchers felt that the elevated frequency of this aberration may relate to an overall increase in gene instability, perhaps increasing the risk of cancer."

This article was reported in the journal:
Cancer Research, 65:2393-2399, May 15, 1996

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