Researchers at the University of California, Davis, MIND Institute have found that exposure to certain synthetic pesticides is linked to a higher risk of autism and developmental delays in children whose mothers were exposed to the pesticides while pregnant.
The study team found that the risk for autism increased from 60 to 200 percent, depending on the type of pesticide used, how close the mother had lived to the treated areas, and when in the pregnancy the mother was exposed.
The risk appeared highest among women who lived near farms, golf courses and other places where commercial pesticides were used during the last trimester of the woman’s pregnancy.
One class of pesticides tested, pyrethroids, was associated with autism and developmental delays when the exposure occurred before conception and in the third trimester. Another pesticide type, organophosphate, was associated with higher autism risk when the mother was exposed during the second and third trimester.
The other two kinds of pesticides the study looked into were organochlorines and carbamates.
Researchers interviewed parents in close to 1,000 families enrolled in a study called Childhood Autism Risks from Genetics and Environment; the families had children ages 2-5 who had autism, developmental delays or who were developing normally. Close to half of the children had been diagnosed with autism, 168 had another type of developmental delay, and 316 were developing as expected.
Parents were given extensive questionnaires about lifestyle and environmental exposures, and where the mothers had lived just before and during their pregnancies.
The study got commercial pesticide application data from the California Pesticide Use Report, which details what pesticides are used, the quantities, and where and when they’re applied. Researchers then mapped the family addresses relative to pesticide application sites.
The report found that the farther the pregnant mothers lived from places that were sprayed with pesticides, the lower the chances of having children with autism spectrum disorders.
Previous studies had found an association between having a child with autism and living near farm fields sprayed with pesticides. Children of farmworkers, who are exposed to ongoing low doses of pesticides before birth and during their first years of life, have a greater chance of being autistic than children who are not exposed to the pesticides.
One in 68 American children is now diagnosed with autism, according to the Centers for Disease Control and Prevention. The disorder has no cure, and no officially accepted cause; but for some years, many scientists and parents have suspected that certain chemicals and environmental pollutants are behind it.
Because autism is a disorder of the central nervous system, any chemical that has been found to harm the nervous system can be a suspected culprit. For example, many parents believe that mercury causes autism; this element is known to be very toxic to the nervous system in higher doses — and mercury-based compounds are used as preservatives in childhood vaccines.
Similarly, many commercial pesticides, including those in the MIND study, damage pests’ nervous systems — this is how the chemicals kill the insects.
Study author Dr. Irva Hertz-Picciotto explained that in an adult human brain, certain chemicals are blocked from getting from the blood into the brain’s tissue by the blood-brain barrier. This barrier consists of cells lining the inside of veins, with gaps between the cells that let some chemicals (like nutrients and hormones) pass into the brain tissue, while other chemicals are kept out.
The blood-brain barrier is not yet fully formed in babies and young children. That could result in pesticide chemicals reaching the baby’s brain nerve cells, the neurons, at a time when they are making necessary connections to each other.
The study was published online recently in the journal Environmental Health Perspectives, of the National Institutes of Health.
Dr. Hertz-Picciotto recommends to families living close to agricultural fields to leave the vicinity, or to keep young children away or close windows on days when pesticides are being sprayed. She also cautions expecting mothers to be extra-vigilant of toxic pesticides, even those that are marketed as “all-natural” for use around the home. She gave as an example pyrethroids, which are based on a chemical from the chrysanthemum flower; however, the synthesized chemicals are much more powerful (and toxic) than the natural compound in the flower.
As a more natural alternative, diatomaceous earth (brand name: Borax) can be used to eliminate pests. Organic gardeners have also had success using certain plants to naturally repel pests, without harming bees, butterflies or humans. These pest-repelling plants include: basil, citronella, catnip, lavender, chrysanthemums, marigolds, sunflowers and garlic.
By Jamell Andrews