Reprinted from (Beyond Pesticides, December 10, 2012) and Neurobehavioral problems following low-level exposure to organophosphate pesticides: a systematic and meta-analytic review.Ross SM, McManus IC, Harrison V, Mason O. Research Department of Clinical, Educational and Health Psychology, University College London , Gower Street, London WC1E 6BT , UK. UCL’s systematic review, published in the journal Critical Reviews in Toxicology
Scientists have found that low-level exposure to organophosphates (OPs) produces lasting decrements in neurological and cognitive function. Memory and information processing speed are affected to a greater degree than other cognitive functions such as language.
The systematic review of the literature was carried out by researchers at UCL and the Open University. It is the first to attempt a quantitative evaluation of the data assimilated from 14 studies and more than 1,600 participants. The researchers used meta-analysis to obtain an overview of the literature and their findings are published in the journal Critical Reviews in Toxicology.
Long-term low-level exposure to organophosphate pesticides produces lasting damage to neurological and cognitive functions, according to the 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.”
“This is considered to be the method of choice in situations where research findings may be used to inform public policy,” explains Professor Chris McManus (UCL Clinical, Educational & Health Psychology), co-author of the study.
Dr Mackenzie Ross continues: “This is the first time anyone has analysed the literature concerning the neurotoxicity of organophosphate pesticides, using the statistical technique of meta-analysis.
“The analysis reveals that the majority of well-designed studies undertaken over the last 20 years find a significant association between low-level exposure to organophosphates and impaired cognitive function.”
Pesticides prevent millions of people from starving to death and from contracting disease, but they are also harmful to humans under certain circumstances. Derived from World War II nerve gas agents, organophosphate pesticides are the most widely used insecticides in the world. They are used extensively in agriculture, by the military and also for domestic purposes.
According to the World Health Organisation (WHO) organophosphate pesticides are one of the most hazardous pesticides to vertebrate animals, responsible for many cases of poisoning worldwide.
The toxic effects of high level poisoning are well established but the possibility that long-term low-level exposure to OPs in doses below that causing acute toxicity causes ill health is controversial.
“In the UK a number of occupational groups have expressed concern that their health has been affected by exposure to organophosphates,” explains Dr Virginia Harrison (Open University), co-author of the study. This includes sheep farmers, who between 1988 and 1991 were required to dip sheep yearly in pesticide formulations containing OPs. Between 1985 and 1998 more than 600 reports of ill health following exposure to sheep dip were received by a government adverse reaction surveillance scheme.
Other groups affected include:(1) Gulf War Veterans, who were exposed to pesticides on a daily basis during their tour of duty to protect them from pests such as sand flies, mosquitoes and fleas which carry infectious diseases (2) airline pilots and cabin crew, who can be exposed to organophosphates in engine oil.
The researchers hope their findings will be of interest to Government advisory committees and departments who are currently reviewing the neurotoxicity of low level exposure to OPs; as well as farmers, Gulf War veterans and aviation workers who believe their health has been affected by exposure to OPs.
Full bibliographic information‘Neurobehavioral problems following low-level exposure to organophosphate pesticides: a systematic and meta-analytic review’ by Mackenzie Ross et al is published online in the Critical Reviews in Toxicology. UCL’s systematic review, published in the journal Critical Reviews in Toxicology
The researchers are hopeful that the results of their analysis will be used to inform governments performing 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.
Through our Pesticide Induced Diseases Database (PIDD) Beyond Pesticides keeps track of the most recent studies related to pesticide exposure. For more information on the cognitive harms pesticides can cause, see our PIDD page on Learning/Developmental Disorders.
Source: Alpha Galileo Foundation [News Release]
All unattributed positions and opinions in this piece are those of Beyond Pesticides.