In 2006, my research caused me to write the following paper. Since then, autism rates went up and government has started looking for sources of airborne mercury.
AUTISM AND MERCURY
AUTISM AND MERCURY
A large body of research has concluded autism is a type of genetic damage that is caused by mercury exposure. 
Autism research looked first to inoculations preserved with Thimerosal as the cause of autism. Thimerosal, which does contain mercury, has been used since the 1930's to preserve inoculations.
[Some] Researchers are now certain Thimerosal preserved inoculations do not breakdown in the body, are definitely not the cause of autism, and the increase or decrease in usage does not relate at all to the incidence of autism rates around the world.  This means the mercury that is hurting kids must be coming from somewhere else.
Incomplete research suggests that somewhere between 15 and 100 human genes are mercury contamination markers related to autism spectrum disorder.  There are thousands of human genes. Damage to just one gene can cause a major birth defect.
Besides autism, many types of neurological problems are caused by mercury. The long list includes: depression, anxiety, attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD).  Many of us could be damaged by mercury exposure and not even know it.
One in twelve women of child bearing age has mercury poisoning.  Mercury is a human neurotoxin with developing fetuses and small children being at greatest risk. Mercury is transferred to babies by way of breast milk.  " … a number of parents of younger autistic children, in whom mercury is more likely to be detectable, have reported higher than expected levels of mercury in hair, blood, and urine samples." 
Hair color, height, race and to some degree personality are controlled by the genetic material of our ancestors. Parents with damaged genes and children who are exposed to mercury during pregnancy are the likely cause of autism.  But, no one knows for sure or no one is telling.
When both parents have genes for a birth defect, their child is more likely to be born with the defect. This means that parents, both with damaged genes, would be more likely to produce a child with birth defects that could include autism. Most of a baby's genetic material comes from the mother.  So, women need to be especially careful to not be exposed to mercury prior to conception and during pregnancy. The same research related to footnote 12 also concluded women should have babies earlier in life rather than later and that most of the cases of autism have nothing to do with the genetic material of the parents but with a mutation that occurs somehow between the sperm and the egg. This conclusion is not currently supported by the bulk of autism researchers.
The largest number of autism cases are in California, Oregon and Minnesota.  Most of the mercury vapor that comes to the West Coast is from Asian countries. The nearly constant on shore air flow coming from overseas encounters a sudden elevation change when it hits the West Coast. This change in elevation causes mercury to condense with water and fall to the ground as rain.  The mercury from China and other Asian countries is a major source of mercury contamination in California rain water. 
Mercury can also accumulate in its dry state on food crops and farm animals. 
It is not a new idea or concept that mercury from industrial sources causes autism, although it was almost unheard of when I started researching this paper in 2005.  The total levels of mercury today far exceed what we as a species have traditionally been used to.  Volcanoes and oceans produce about a third of the mercury in the air, meaning mankind has tripled the amount of airborne mercury by industrialization. 
The Environmental Protection Agency concludes 45% of all vaporized mercury from coal fired power plants falls to the earth within an area of about 30 miles from the power plant.  The remaining 55% goes up into the atmosphere to float around the earth. " … virtually all of the mercury deposited west of Minnesota and the Mississippi River [comes] from outside the United States."  Even the Arctic Circle has been contaminated with dangerous levels of mercury in nearly all forms of life. 
China produces about 1 billion pounds of vaporized mercury per year, mostly from coal fired power plants. Asian countries as a whole contribute about half of the industrial mercury belched into the atmosphere.  The United States allegedly produces only 257,600 pounds of airborne mercury per year. 
In America, about 88% of the mercury released into the planet's atmosphere comes from burning coal. About 10% of our homespun mercury vapor is from crude oil and the things made out of it.  Only 2% comes from other sources for mercury like cement manufacturing, burning of medical, municipal and hazardous waste, pulp and paper milling, and mining.
S. Mark Wilhelm, Ph.D., a government researcher, told me about half of all the crude oil mercury ends up in asphalt. (see footnote 25) Logic dictates asphalt would continue to evaporate mercury forever, more so on hot days.
Perhaps the combination of the large amount of highways and streets in Southern California and the sometimes severe heat here cause a larger amount of mercury in the local air than other regions.
According to Dr. Wilhelm, elemental or "ethyl" mercury is generally considered to be safe because most of it goes harmlessly into the high atmosphere to gradually break down over a year or so.  "Some" of this mercury does eventually oxidize and comes down to us as rain.
Through a process of combining with bacteria, the mercury in our rain becomes organic methylmercury. Fish eat the methylmercury containing bacteria, the big fish eat the little fish and then we then eat the big fish. Methylmercury vapor is also released by plants growing on contaminated soil. 
Methylmercury that ends up in fish has caused major concerns about the fishing of California, Oregon, Minnesota and Florida. The State of California has issued warnings that pregnant women should not eat fish very often or at all. Forty-seven other states have also issued similar warnings against eating local fish because of mercury contamination. 
It is not just fish that can be contaminated. People can be contaminated by everything they eat and by chemical exposure to their skin and lungs. The process of being exposed and contaminated by mercury over time is called "bioaccumulation".  After the passage of time, the mercury eventually gets to a toxic level in anyone continually exposed to it.
Standards for airborne contaminants are set by our government.  However, air quality standards, have not been established for many hazardous air pollutants. Hazardous air pollutants are chemicals known to cause or suspected to cause immediate or long-term serious health effects such as cancer, reproductive effects or birth defects, or adverse environmental effects. Mercury has no national standards set for its regulation other than plans to clean up domestic coal fired power plants. United States industry still sells and builds hazardous coal fired power plants in other countries.
The South Coast Air Quality Management District (SCAQMD) is the local agency that tests for airborne contaminants in Southern California. SCAQMD does not do any testing for vaporized mercury in the air. They do require businesses to comply with vaporized mercury standards in their production of products.
There are other sources for mercury contamination. California and many other states experienced a gold mining boom 150 years ago. A necessary part of gold ore purification is mercury. 220,000,000 pounds of elemental mercury was mined from California sources with little or no regulation.  The total amount of mercury lost to the California environment between the 1860's through the early 1900's as a result of mining is estimated at about 12 percent of the amount mined or 26,000,000 pounds.
Because much of the mercury ore from mining was dumped on the ground or into lakes, some of the elemental mercury has percolated down into the water table, the source of drinking water. This same mercury continues to evaporate into the air as time goes by.
The drinking water of over 8 million Californians has been contaminated with mercury. Of those 8 million California citizens, 329,169 have been contaminated with mercury over the health based limits of California. (see footnote 32)
Santa Fe Springs is a city in Orange County and Corona is a city just North of Orange County. These two cities represent two of the five most mercury polluted drinking water communities in California.  A reasonable inference is that if the communities surrounding Orange County have unusually high levels of mercury in their water, then the whole water table in the Orange County area is contaminated.
It costs 3.5 million dollars to provide for the average autistic person over their lifetime.  Autism cannot be cured, it's genetic.
© 2006 Mark Reman Hamilton, Esq.
Law Office of Mark R. Hamilton
2942 E. Chapman Ave., 322
Orange, California 92869