Organophosphate pesticides were once commonly used in roach control and other applications but organiphosphates were originally developed as nerve-gas agents for chemical warfare. The human body converts organophosphate pesticides into altered forms called metabolites, and  organophosphates are toxic to the nervous system, known to cause memory and vision problems.

Organophosphates are also vital biochemicals that include DNA and RNA. However, there are safer ways to get rid of household pests and the EPA bans organophosphate pesticides for home use, but when studies showed health effects, somewhat sketchy papers began to link organophosphates to things like ADHD and if a child does not do well in school, though organophosphates were in common use decades ago. Organophosphates became widely employed both in natural and synthetic applications because organic groups can be linked together easily.

A new review reaffirms that low-level exposure to organophosphates (OPs) produces lasting decrements in neurological and cognitive function and that memory and information processing speed are affected to a greater degree than other cognitive functions such as language.  The toxic effects of high-level poisoning are well established but the possibility that long-term low-level exposure to organophosphates in doses below acute toxicity can cause ill health is controversial.

A systematic review did a quantitative evaluation of the data assimilated from 14 studies and more than 1,600 participants. The researchers then used meta-analysis to obtain an overview of the literature about the question they asked in their systematic review.

"Meta-analysis combines the results of several studies and moves the discussion away from individual pieces of research, towards an overview of a body of literature," saids Dr. Sarah Mackenzie Ross, psychologist at University College London and lead author of the paper.  A systematic review involves examining the literature to ask an answerable question and a 
 meta-analysis is the statistical approach to combining the data from a systematic review.

"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, also a psychologist at University College London and  co-author of the study. 

They say this is the first time anyone has analyzed the literature concerning the neurotoxicity of organophosphate pesticides using meta-analysis, though that is hard to believe. The EPA banned organophosphate pesticides for home use 11 years ago. 

Pesticides prevent millions of people from starvation and disease, but all pesticides, be they synthetic or natural,  can be harmful to humans. Organophosphate pesticides as a class remain the most widely used insecticides in the world. 

"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 of 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.

 Published in Critical Reviews in Toxicology.