There are many different opinions on what causes autism spectrum disorders, but they can be divided into two main camps. One camp of scientists, researchers and parents believe that autism is genetic and the other camp believe that autism can be triggered or caused by environmental factors.

PCBs

One environmental factor that is thought to cause autism is a chemical which was actually banned in the USA thirty years ago, polychlorinated biphenyl, known as PCBs. PCBs manufactured from the 1920s and were commonly used in pesticides, flame retardants, caulking and electronic components, before being banned in 1979 in the US because of their health damaging properties.

Even though they are no longer used in industry, PCBs are still present in our environment, because they do not biodegrade very easily, and can still be present in our drinking water, air, soil, food that we eat (contaminated fish, produce grown in contaminated soil etc.) and products that were manufactured before the ban.

This is worrying because studies have shown that PCBs can cause cancer (particularly breast cancer) and can damage the main systems of the body – the endocrine system, nervous system, reproductive system and immune system. PCBs also accumulate in our body fat over time, meaning that they are stored rather than excreted, and can also contaminate blood and breast milk.

A 2008 news report reported that PCBs had been found in a hard wood floor finish that had been popular in the 1950s and 1960s, and researchers found that homes with the PCB-containing wood floor finish had significantly high levels of PCBs in the air and dust, and that the occupants had high levels in their blood over 40 years later!

Research into PCB Exposure

Studies have not only shown that PCBs can cause cancer and damage to the main body systems, they have also suggested that PCBs can cause developmental and behavioral problems in children. However, although the link was there, scientists were unsure of how PCBs were causing these problems, until recently.

In 2009, a study by the University of California Davis Center for Children's Environmental Health found that PCBs affect the development of brain cells and cause the brain circuits to become "overexcited", thus causing developmental problems. The Center's director, Isaac N. Pessah, PhD, co-author of the group of studies, said:

"We think we have identified the way in which a broad class of environmental contaminants influences the developing nervous system and may contribute to neuro-developmental impairments such as hyperactivity, seizure disorders, and autism."

One of the group of studies found that animals that were exposed to low doses of PCBs exhibited difficulties learning to swim a maze (a problem used to test learning in animals) and the plasticity of their dendrites was adversely affected. Pamela Lein, PhD, an associate professor of neurotoxicology at the University of California Davis School of Veterinary Medicine, said that this plasticity was crucial for memory and learning, and that problems with dendrite plasticity and growth have been linked to autism, schizophrenia and mental retardation in the past.

Another of the studies looking at the effects of

PCB exposure on animals' hippocampus area of the brain (the part that regulates emotion and memory), found that the PCB exposure caused excitability in the neurons. This type of excitability can cause autism and other neuro-developmental disorders. When scientists looked at the brain on a cellular level, they found that PCBs bind to the cell receptors and affect calcium release. Calcium is needed to maintain normal signalling between cells.

PCBs and Autism

These studies definitely back up the results of previous studies which have suggested a link between PCBs and developmental disorders, like autism. The University of California San Francisco (UCSF) had already concluded in 2007, from tests on rats, that PCBs disrupt the part of the brain that is shown to be impaired in autistic children, the auditory cortex. The auditory cortex is is needed for the proper processing of sounds and for language development, and when it is disrupted there is an abnormality in the signals that are sent by the brain to react and respond to sound. This signaling imbalance could be responsible for the language impairments and communication problems that many autistic children suffer from.

Many scientists believe that the PCBs in our environment are causing disruption to the brains of children who are predisposed to this type of sensitivity, and that's why not all children suffer from developmental disorders like autism. Research is ongoing, but PCBs do seem to be linked to autism.