Autism and the Environment

A Link Between Toxins and Autism?

Although there is still much research to be done, current studies suggest a link between environmental exposure to certain toxins (e.g., heavy metals, such as mercury and lead; household plastics; and chemicals, such as pesticides) and the soaring rates of autism in our population. These toxins are more prevalent today than in the past. Those with ASD, or at risk for ASD, may be especially vulnerable to them. For example, many children at risk of developing autism may have a metabolic impairment that reduces their ability to metabolize and detoxify, so that they have trouble ridding their bodies of heavy metals and other toxins. Build up of these toxins in the body can lead to brain and nervous system damage and developmental delays, and can chronically affect brain function and reduce health and well-being throughout life.

Toxins and other environmental factors can contribute to autism at various points in an individual’s development. Toxins don’t have to kill people or cells in their bodies to cause harm. They can change how the brain and body develop, and how they function.

Toxic exposures before birth can affect the development of the brain and nervous system, as well as other systems of the body. After birth, they can affect later stages of development. Exposures at any point can affect the health of the cells in our body, which can lead to loss of health and development of disease.

If toxins alter the health or function of cells in our brains, the cells may not be able to work so well in helping us to use our brains. Our brains may get more “irritable.” This can cause changes and problems in the way we think, learn, process sensory information, sleep and handle stress.

Toxins are a lifelong problem, not just a developmental problem. Many people with autism are very sensitive and reactive to exposures throughout life. They can have ups and downs that can be traced not just to stress but also to chemicals and allergens. 

Research dollars have only recently started to support the systematic evaluation of environmental toxins as possible risk factors for ASD. No “single cause” has emerged. One reason is that many potential contributors to autism can have similar effects. Many different kinds of chemicals can impact similar vulnerable parts of our systems. Also, many different genes can target the same or related pathways.

 Because many seemingly environmental and genetic risks converge, no single cause of autism may ever jump out at us from the data. Instead, we need to take seriously the potential harm that can be caused by various combinations of factors, even if there is no single one responsible.

The Need for Chemical Policy Change

Many public health and environmental groups are citing the danger of combined chemicals in requests for federal chemical policy reform. To address this need, refinements to the Toxic Substances Control Act (TSCA - http://www.epa.gov/oecaagct/lsca.html) and the newer Kid Safe Chemical Act are now being drafted for consideration in Congress.

To understand the need for chemical policy change, one must understand how chemicals are now tested. Currently, 60,000 manufacturing chemicals are “grandfathered” and exempt from any testing, while others are tested one at a time, with a “safe” level of human exposure established. The “safe” level is the level of human exposure allowed before that exposure becomes toxic. Chemicals are not tested in combination. They are not restricted if they disrupt our bodies’ signals, like hormones or neurotransmitters, at a level lower than the “safe” level. It is these combined and lower level exposures that are suspect and require investigation.

The complexity extends to neurotoxicology testing. At present, there is no requirement to test chemicals for their impact on the extremely sensitive developing nervous system. Of the approximately 3,000 chemicals produced in the largest volumes, only 20-30 have been tested using the EPA’s developmental neurotoxicology protocol. Because of this, we do not have any information regarding the effects on the developing human body and brain from exposure to most chemicals, particularly those in low doses or in combinations.

Other Possible Environmental Causes

The need is apparent for government, scientific, medical and autism communities to probe further into all possible environmental causes of ASD in a fair and thorough way. Findings may help us approach treatment and prevention more effectively. For example, many studies implicate mercury in autism or in problems that are found in autism. Two studies have shown increased autism with increased airborne mercury (from air pollution). Mercury injures the immune system, causes brain inflammation and affects brain development. Several studies have shown that children with autism have elevated porphyrins, which are a sign of excessive mercury exposure. But other chemicals can also have some of these effects, so even though mercury is clearly harmful, it may be hard to prove that it is a central cause of autism.

Some have focused on chemicals in childhood vaccines as suspected agents in the onset of autism. Serious investigation needs to be done on the impact of vaccines and the chemicals in them, in conjunction with other environmental exposures. The research we need includes, but is not limited to, investigating whether thimerosal- containing vaccines (TCVs), the measles-mumps-rubella (MMR) inoculation and/or a combination of the two play any causal or contributory relationship to autism or susceptibility to autism in the population at large or in vulnerable subgroups. It is important for studies to look for ways that these or other exposures may cause or aggravate harm in combination with other factors even if they are not the sole cause. The more we learn about how people can be different from each other in terms of their vulnerabilities, the more we need to consider how some people can be injured by exposures that might be easily tolerated by others.

In the absence of a cure, improving the physical lives of people with autism now relies on largely bolstering weak pathways with nutrition, rest and stress relief, while removing specific irritants in the body or environment that aggravate symptoms. We need to identify pathways and their solutions in a manner that both addresses the heterogeneity of autism and identifies common workable solutions. Science, participatory research and regulatory reform have much to contribute to this effort in the coming years.

For more information, see Autism and the Environment 101: http://www.autism-society.org/site/PageServer?pagename=research_envirohealth_101.

For more information on participatory research, see Treatment Guided Research Initiative: http://www.autism-society.org/site/PageServer?pagename=research_TGRI.

1.  Claudio, L, Kwa, W.C., Russell, A.L., & Wallinga, D. (2000). Testing methods for developmental neurotoxicity of environmental chemicals. Toxicol Appl Pharmacol, 164(1):1-14.