Some pesticides can disrupt the development of the brain and nervous system at extremely low doses. A study published in October 2006 provides key new insights into how and why (Slotkin et al., 2006).
The organophosphate (OP) class of insecticides includes some of the most dangerous pesticides still in widespread use. This family of chemistry has been the dominant focus of the Environmental Protection Agency (EPA) in the implementation of the “Food Quality Protection Act,” major legislation passed in 1996.
Whether and how OPs can disrupt the development of the brain and nervous system has been one of the hottest areas in developmental biology. Major strides have been made in understanding how certain pesticides that impact the endocrine system can block, or over stimulate certain key developmental stages. The just-published study shows that OP insecticides disrupt brain development through a variety of impacts on the serotonin system. (Serotonin is a hormone-like neurotransmitter).
The study reaches two key conclusions with important implications on pesticide risks. First, different OP insecticides impact the functioning of the serotonergic system in different ways, and hence can trigger developmental abnormalities in the brain and nervous systems through different mechanisms. The EPA continues to regulate all OP insecticides as if they impair health through the same mechanism, an assumption that is not supported in the case of developmental neurotoxicity.
Second, Slotkin et al. (2006) found that some OPs impair neurological development at doses four to five-times lower than the doses causing detectable levels of acetyl cholinesterase inhibition. The EPA cumulative risk assessment of the OPs concluded that OP uses and residues in food meet the FQPA’s strict new safety standard. The problem is, however, that the EPA focused on cholinesterase inhibition as the common mechanism of OP toxicity, not developmental neurotoxicity. Recent science shows that developmental problems can be triggered by OP exposures far lower than what EPA has deemed “safe.”
For many years the scientific community has been more concerned about the developmental neurotoxicity of OPs, in contrast to the typically transient inhibition of cholinesterase in the blood or brain. This study points clearly to the need for EPA to revisit and update the OP risk assessment, this time based on developmental neurotoxicity. Almost certainly, new regulatory restrictions on OP use will be necessary to prevent developmental risks from OP residues on fruit and vegetable crops.
Sources: “Organophosphate Insecticides Target the Serotonergic System in Developing Rat Brain Regions: Disparate Effects of Diazinon and Parathion at Doses Spanning the Threshold for Cholinesterase Inhibition.”
Authors: Theodore A. Slotkin, Charlotte A. Tate, Ian T. Ryde, Edward D. Levin, and Frederic J. Seidler
Environmental Health Perspectives, October 2006, Vol. 114, No. 10: pages 1542-1546. Accessible below, or free of charge at
“Successes and Lost Opportunities to Reduce Children’s Exposure to Pesticides Since the Mid-1990s.”
Authors: Charles M. Benbrook, Alan Greene, Chensheng Lu, and Philip Landrigan
Organic Center “Critical Issue Report” 2006.1. 41 pages.
Accessible free of charge at