There is no one known cause for autism, or Autism Spectrum Disorder (ASD), but researchers are studying whether environmental factors play a role in the development of ASD. Exposure to certain chemicals, for instance, may be related to the development of autism. Also associated with an increased risk of autism are some harmful substances ingested by pregnant women.
Heavy metals such as mercury are more prevalent in our environment today than they have been in the past. Individuals who have ASD or are at risk for developing it have a decreased ability to detoxify and metabolize these toxins.
Not only are heavy metals more prevalent; the incidence of autism is on the rise as well. University of California-Davis researchers have reported that the incidence of autism has risen in California from 205 in 1990 to more than 3000 in 2006. Over the past 15 years, nationwide autism diagnosis rates have also risen dramatically. This increase has led researchers to “start looking for the environmental culprits responsible for the remarkable increase in the rate of autism in California,” according to Irva Hertz-Picciotto, epidemiology professor at University of California-Davis, who led the study.
Many researchers believe there may be a connection between a pregnant woman’s exposure to chemical pollutants, metals and pesticides in particular, and the alteration of a developing baby’s brain structure that triggers autism.
Chemicals in the environment that alter how the brain grows include mercury, polychlorinated biphenyls (PCBs), bromated flame retardants, pesticides, and lead. Exposure to PCBs has decreased in recent decades, but exposure to other chemicals such as insecticides and flame retardants has risen.
One study has found that mothers of children with ASDs were twice as likely to use pesticide-containing pet flea shampoos; another study has found a link between compounds used in vinyl and cosmetics and an increase in autism. Hertz-Picciotto reports that products like antibacterial soaps can change immune systems and therefore harm to brain.
Also potentially altering the immune system could be a new infectious microbe (a virus or bacterium) to which infants and fetuses might be exposed. Autism rates in the 1970s increased due to the rubella virus.
In short, according to Hertz-Picciotto, causes of autism could be “in the microbial world and in the chemical world.”
Research regarding the link between vaccines and autism, however, has not been proven by research. The Centers for Disease Control and Prevention has conducted numerous studies on the safety of vaccines and the link between thimerosol, a preservative used in vaccines. The studies have found the there is no association between autism and vaccines.
Read more about the UC Davis study here.