Organophosphate pesticides cause lasting damage to brain and nervous system

Long-term low-level exposure to organophosphate pesticides produces lasting damage to neurological and cognitive functions, according to researchers at University College London (UCL). This research pulls data from 14 studies over the past 20 years, including more than 1,600 participants, in order to provide a quantitative analysis of the current literature on these dangerous chemicals. Lead author of the study, Sarah Mackenzie Ross, Ph.D., notes, “This is the first time anyone has analyzed the literature concerning the neurotoxicity of organophosphate pesticides, using the statistical technique of meta-analysis.”

UCL’s systematic review, published in the journal Critical Reviews in Toxicology, comes to an unsettling conclusion about the hazards of constant low-level occupational exposure to organophosphates. The study notes, “The majority of well designed studies found a significant association between low-level exposure to [organophosphates] and impaired neurobehavioral function which is consistent, small to moderate in magnitude and concerned primarily with cognitive functions such as psychomotor speed, executive function, visuospatial ability, working and visual memory.” In other words, low-level exposure had significant detrimental effect on working memory and information processing.

The researchers are hopeful that the results of their analysis will be used to inform governments preforming reviews on the neurotoxicity of low level exposure to organophosphates. Co-author of the study, Professor Christopher McManus, M.D., Ph.D., explains, “This is considered to be the method of choice in situations where research findings may be used to inform public policy.” Although the study was directed at apprising the UK government, Beyond Pesticides would like to see this research affect registration reviews performed by the U.S. Environmental Protection Agency (EPA).

Organophosphates, derived from World War II nerve agents, are a common class of chemicals used as pesticides. Several are already banned or highly restricted in several European countries and in the U.S., where most are still widely used. In addition to being potent neurotoxins, organophosphates pesticides are extremely harmful to the nervous system, as they are cholinesterase inhibitors and bind irreversibly to the active site of an enzyme essential for normal nerve impulse transmission. Despite numerous organophosphate poisonings of farmworkers, homeowners, and children, EPA has allowed the continued registration of many of these products. In some cases, such as those of chlorpyrifos and diazinon, household uses of the products have been cancelled because of the extreme health risks to children, but agricultural, golf course, and “public health” (mosquito control) uses remain on the market. Furthermore, the cancellation of household uses does not restrict the use of remaining stocks, meaning homeowners who purchased diazinon, for example, before the 2004 phase-out, may still use this product. Malathion, another common organophosphate, is still permitted for residential use as an insecticide and nematicide, even though all organophosphates have the same mode of action in damaging the nervous system. According to EPA, approximately one million pounds of malathion are applied annually for residential uses. After a protracted battle with farm worker and environmental groups, EPA acted to phase out all uses of the dangerous organophoshate azinphos-methyl (AZM), however the agency has allowed growers to use their remaining stocks through September 30, 2013.