Are pesticides related to the development of autism?

 

 

Recently there has been some news coverage on the possible connection of pesticides with the development of autism spectrum disorders (ASD). While I am thrilled that the connection between environment and mental health is getting covered, I prefer to read the actual research to determine what is being found, and how the data was collected.

The literature on pesticides and ASD is very limited, however what is available is very interesting.

In 2007 Roberts and colleagues published their findings looking at a potential connection between ASD and exposure to pesticides. They were specifically interested in pesticides which were troubling to the area population, as well as those thought to have a negative effect on health. In total they ended up looking at 54 pesticides.

The study took place in central California (Roberts et al, 2007). In may ways a study linking autism and pesticide usage could only be done in California. California is home to the California Department of Pesticide Regulation which regulates the use and sales of pesticides (CDPR, 2013). It also has the Regional Center, a division of the Department of Developmental Services, which provides services to individuals diagnosed, or at risk of, developmental disabilities (CDDS, 2014). Using information from these two departments Roberts and colleagues (2007) were able to link pesticide usage and instances of ASD and then compare pesticide usage with a control group matched on race/ethnicity, maternal education, and residing in the same geographic area (defined by the regional center boundaries; Roberts et al, 2007).

The study was specifically interested in crucial neural development, specifically the first trimester of pregnancy when the brain is developing (Roberts et al, 2007). To analyze the data researchers then broke the time periods up into two month increments starting at 300 days before conception and ending at 300 days after conception, spanning the entire period of a typical gestational period.

The pesticides containing Organochlorine, such as dicofol and endosulfan, was significantly related to the occurrence of ASD within the area of slightly more than one mile (Roberts et al, 2007). It is only after this radius that the effect of organochlorine in relation to the development of ASD becomes non-significant. They found that biggest area of effect was slightly less than a month after conception, following the neural tube closure, the area that will later develop into the brain (Roberts et al, 2007). Children of mothers who were exposed to organochlorine within this span of 26-81 days were 7.6 times more likely to later be diagnosed with an ASD diagnosis (Shelton, Hertz-Picciotto, & Pessah, 2012).

Using the same data and reanalyzing it using a statistical technique which did not require data to be analyzed using specific time periods, Roberts and English (2012) replicated the findings in the previous study and found an additional area of concern after birth when children were between the ages of 3 to 9 months old (Roberts & English, 2012).

Evidence is continually mounting that suggests a relationship between pesticide use and the diagnosis of ASD. Shelton and colleagues (2014) recently released a study looking at pesticide exposure to mothers in an ongoing Childhood Autism Risks from Genes and Environment (CHARGE) study, which is also based in California. Instead of using population based samples, the researchers interacted with over 1,600 participants via surveys (Shelton et al, 2014). While the majority of participants were also recruited through the Regional Centers, some participants were recruited through additional outreach, which hopefully increases representation of individuals on the spectrum who are higher functioning and may not qualify for Regional Center services.

Shelton and colleagues (2014) found that children later diagnosed with ASD were 60% more likely to have been exposed to organophosphate pesticides and 150% more likely to have been exposed to carbamate pesticides. Like Roberts et al (2007) they determined exposure based upon where the participants lived (Shelton et al, 2014).

The time period in which participants were exposed to various pesticides may impact development. For example exposure to organophosphate had a greater impact in the second and third trimester of pregnancy, while pyrethroids had a greater impact during pre-conception and the third trimester (Shelton et al, 2014).

The research concerning the linkage of ASD and pesticides is still pretty limited. However, what is available has all shown an impact if the exposure occurs during prenatal or early development. There is still no research looking at exposure to pesticides in diet in not only the early development, but also through the life span.

If you already have a child diagnosed with ASD, then this research will not help you out much. Although, it may help explain the rise in ASD rates, I think it really just opens up more questions.

Practically, if you are moving you may want to look at any potential exposure to pesticides. It is also evidence in support of more organic farming.  

 

 

Reference

California Department of Developmental Services. (2014). Who is eligible for services? Retrieved June 25, 2014 from http://www.dds.ca.gov/General/Eligibility.cfm

California Department of Pesticide Regulation. (2013). Retrieved June 25, 2014 from http://www.cdpr.ca.gov/

Roberts, E. M., English, P. B., Grether, J. K., Windham, G. C., Somberg, L., & Wolff, C. (2007). Maternal residence near agricultural pesticide applications and autism spectrum disorders among children in the California central valley. Environ Health Perspec, 115, 1482-1489.

Shelton, J. F., Geraghty, E. M., Tancredi, D. J., Delwiche, L. D., Schmidt, R. J., Ritz, B., Hansen, R. L., & Hertz-Picciotto, I. (2014). Neurodevelopmental disorders and prenatal residential proximity to agricultural pesticides: The CHARGE study. Environ Health Perspect; http://dx.doi.org/10.1289/ehp.1307044

Shelton, J. F., Hertz-Picciotto, I., & Pessah, I. N. (2012). Tipping the balance of autism risk: Potential mechanisms linking pesticides and autism. Environ Health Perspect; http://dx.doi.org/10.1289/ehp.1104553