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For years, parents have traded stories online, seeking answers about their child’s mysterious disability.  This month, a newly published analysis shows the strongest correlation yet between autism and prenatal exposure to pollution.  Other smaller studies previously suggested a connection, but science is cautious to confirm findings until the results can be repeated in larger-scale projects.

The new study uses pre-existing data, in the form of insurance claims for over 100 million United States residents, to show that patterns of autism match patterns of pollution-caused birth defects.

Andrey Rzhetsky, lead author of the study, explains “Malformations predict very strongly the rates of autism, and the rate of malformation per person varies significantly across the country.  Some counties have low rates and some have very high.  And rate of malformations is higher in counties with higher rates of autism.”

To break it down further, certain congenital malformations — birth defects — are widely accepted as caused by pollutant exposure.  Researchers discovered that a 1% increase in these malformations correlated with a 283% increase in Autism Spectrum Disorder (ASD) diagnoses within the same geographical area.  Keep in mind that a 1% increase in a specific malformation — in this case, problems with the male reproductive organs — makes a big difference.

Nationwide, the average for this problem is 0.2687%, meaning less than 3 out of 1000 boys are affected.  At 1%, we have 10 out of 1000, and in the county with highest incidence 2.4%, or 24 boys are affected.  Other counties reported zero.   While the CDC estimates nationwide rates for ASD at 1 in 88, in areas of elevated congenital malformations the ASD rate can more than triple.  Local gene pools and access to services may both play a role, but some researchers now believe the significant difference between county ASD rates involves exposure to environmental toxins which harm the developing fetus, known as teratogens.

Just last month, a report in Lancet Neurology named six new chemicals to the list of neurotoxins affecting fetal brain development.  Consensus is growing that teratogens are a major factor in autism — what we still don’t know is which specific chemicals to blame.  Rzhetsky believes his study simply points a direction for much more research to come.  It’s still too soon to draw firm conclusions about the role of environmental toxins versus genetics, both of which are probably important.  Though nearly one in three siblings of ASD-affected children also show developmental irregularities, can we chalk that up to shared genes, or shared contaminants?

Although a 2010 study identified ten major “autism clusters” in California urban areas, the researchers concluded the apparent disparity was explained by the higher level of education in those areas, leading to greater access to services and diagnosis.  This new study throws that conclusion into question: California’s cities are among the country’s most polluted.  What type of pollution?  Watch out for air pollution, according to one Harvard study released last summer.  Airborne teratogens known to affect fetal brain development include diesel particulates, lead, manganese, mercury, and methylene chloride.  These toxins are released by industry, vehicles, and home heating systems.

Recent Related:

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Autism’s ‘Patchwork’ begins during pregnancy

The air pollution for your area may be affected by air currents transmitting particles from factories hundreds or thousands of miles away.  Even in the protected forests of our national parks, the air can be nearly unbreathable at times.  In the big picture, children diagnosed with ASD may be unwillingly standing in for the canary in the coal mine.  The miners couldn’t see or smell the carbon monoxide, but when they saw the canary fall off her perch, they knew to run for their lives.  Dying scallops are playing a similar role for ocean acidification.

As the light begins to dawn on the causes of autism, we struggle to find ways to protect the next generation of unborn children.  For families affected by ASD today, the news may be both gratifying and frustrating.  Though we’re scratching the surface of the overwhelming “why?”, pointing fingers does little to help kids’ daily functioning and future prospects.  Research and word-of-mouth evaluate a spectrum of treatments for ASD, with dietary changes often giving notably better results than prescription drugs in parent-reported effects.  For now, caregivers often fall back on personal reports or subjective survey results, due to the lack of traditionally validated studies.

How can I protect my family from pollution?

Pollution, often invisible to the senses, can raise feelings of despair and helplessness.  To live, we need to breathe air, drink water, and eat food, each of which are subject to contaminants beyond our control.  But clearing the air starts at home.  Indoor air pollution is often worse than outdoor, and reducing use of toxic products, including cleaners, furnishings, and paint, can lighten our bodies’ load.  If possible, make choices that allow you to spend less time in traffic, especially during pregnancy.  As a pedestrian, stick to side streets, and if you’re choosing a new home, look in places away from highways and arterials.  All major roads produce dangerous levels of hazardous particles with both known and unknown health risks.  Traffic-related pollution in Paris is now so severe that the French government has instituted a partial driving ban, with temporary free public transit to discourage car use: many large cities are approaching or past that critical point.  Ultimately, it may take similar regulations or incentives to make a real difference in the air quality of US cities.

Even more troubling is the industrial pollution we breathe and eat every day.  Coal-fired power plants spew airborne mercury into clouds which can travel hundreds of miles before precipitating onto lakes, rivers, and farmland.  If air pollution is high in your region, you may consider purchasing an indoor air cleaner; water filters are increasingly recommended for most homes.

Will Rzhetsky’s new findings end the tense debate which has simmered (and raged) for years among doctors, parents, and researchers?  No.  Already, his conclusions are being dissected and interpreted among those who have their own alliances in the debate.  Though those who have argued a link between vaccines and autism have also relied on the contaminant theory, Rzhetsky’s results don’t clearly support a link with vaccines.  Vaccines are given uniformly across the US, so the distinct geographical clustering means something different is going on.

We don’t need a universal consensus around causation to take action around disturbing trends in environmental pollution, whether or not we are personally impacted by autism.  A million tiny ripples of change can add up to a wave.  We can get involved in reducing industrial coal-burning, support legislation and technology to decrease vehicle emissions, or simply begin changing our daily habits as we spread awareness of our impact on the earth.  Rzhetsky called his findings “a strong environmental signal”.  Lately, such “signals” are sounding like sirens from many corners.  Together, they may be the global alarm clocks required to wake us up.