Estimated gestational pesticide exposure and offspring autism

Maternal proximity during pregnancy to areas treated with various agricultural pesticides may increase the risk of offspring autism according to a new study by Janie Shelton and colleagues* based at the University of California, Davis in the United States.

Drawing on an analysis of data reporting commercial pesticide use – chemicals used to control various pests which can adversely affect crop yields and health – in the state of California, researchers were able to analyse several variables on the types of pesticides in use, where they were used and in what amount. This information was cross-linked with information derived from the CHARGE (Childhood Autism Risks from Genetics and Environment) study looking at residential addresses during pregnancy for confirmed cases of autism spectrum disorder (ASD) and developmental delay (DD) compared with asymptomatic controls. The authors concluded that

“proximity to organophosphates at some time during gestation was associated with a 60% increased risk for ASD”.

Organophosphate (OP) pesticides are a popular class of insecticide which act as nerve agents primarily affecting the enzyme acetylcholinesterase found in various insects and animals. Such inhibition of acetylcholinesterase mimics the effects of various nerve agents such as the chemical weapon sarin.

Timing of exposure during pregnancy was also found to be potentially linked to risk of offspring autism as a function of OP and other pesticide exposure. By contrast, multiple exposures to various different types of pesticides did not seem to increase the risk of autism over and above that seen for individual classes of pesticides. The authors conclude by suggesting that their results

“strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures”.

These are potentially important findings which add to various other research suggesting a link between elevated risk of offspring autism and environmental variables. Indeed, other analyses derived from the CHARGE study have implicated air pollution as another potential correlate. The next stage, as the authors suggest, is further research on how genetics and such environmental exposures may interact to “reveal vulnerable sub-populations”.

Importantly however, there are several limitations to the current study. No direct measure of pesticide exposure for individuals is provided including any results from biological testing of such pesticides and their metabolites in either mothers or children. Estimates of pesticide exposure are instead used and generalised to group proximity to such events. The reliance on commercial pesticide use data also misses out on any non-commercial uses of such compounds such as those used in homes or gardens. There is likely therefore an under-estimating of actual exposure values. Authors also provide only speculation on the possible mechanisms involving pesticide exposure and risk of offspring autism.

Pesticides represent an important class of chemicals which confer several benefits in terms of food security and the elimination of pests which can cause disease. They do however require great care and caution with their administration as a result of some well-known and sometimes very extreme side effects associated with accidental or purposeful exposure. With further research required in this area, minimising exposure to such agricultural chemicals during pregnancy would seem to be a sensible approach.

 

* Shelton JF. et al. Neurodevelopmental disorders and prenatal residential proximity to agricultural pesticides: The CHARGE study. Environ Health Perspect. 2014: June 23.

Read more about this paper here: http://questioning-answers.blogspot.com/2014/06/pesticides-and-autism-chapter-ii.html