KOMU's Ashley Reynolds delved deep into what some parents think is the only reason their children have autism. The root of the debate stems from something invisible to the eye, but for some its possible effects are devastating to see.

You cant see it, but it's in there. One of the most toxic elements on earth is in vaccines. Thimerosal is a mercury-containing organic compound used in some vaccines as a preservative. Eli Lilly started selling thimerosal in the 1930s and the pharmaceutical company will reportedly profit from this compound until 2010.

According to Dr. Haley there were no cases of autism before 1941. He also says thimerosal was invented in 1928, put into biologicals in 1932, and increased exposure to organic material.

"This is a modern man disease and when people say, 'Oh we had it before," yeah there was mercury around before a lot of the snake oils. Mercury isn't rare, but we didn't have the level of autism as we had after we introduced thimerosal as a biological material," he explained.

A generation of children born in the 1990s is at the heart of the current debate. From the early 80s to today, the number of vaccines given to American children has more than tripled, tripling mercury intake at the same time. The amount of mercury an American child like Adam from Kansas received in the 90s from vaccines is around 237 micrograms. Just like any child, Adam didn't receive all those vaccines at once, but he did get multiple shots at each appointment amounting to about 50 micrograms per visit.

We all encounter mercury in our environment and our bodies work to get rid of, or excrete, it. The larger you are, the easier it is to excrete mercury. In fact, EPA standards say a person large enough to be able to excrete the 50 micrograms from a single office visit would have to weigh 1100 pounds. The reason size matters is a naturally occurring compound in our bodies called gluthione. Generally, larger people have more of it. But researchers who study possible biochemical causes for autism say children with the disorder have far less glutathione than normal, even for their small size. According to them, this explains the correlation between increased vaccines and increase autism rates.

In the 1970s when children received a third of the vaccines they do now, doctors diagnosed one out of 10,000 kids with autism. Today that number is around one in 150.

For those who don't see the link to vaccines, they say the spike in autism cases comes from better diagnoses and the fact that the autism spectrum has grown to include aspergers and other disorders marked by communication problems and repetitive behaviors.

"It's probably better diagnosing. I think what has also happened is we are diagnosing many, many children with autism now that weren't diagnosed in the past, because we used a much more rigid diagnostic criteria. Fifteen years ago to get an autism diagnosis, you really had to have what we call autistic disorder-severe classical autistic disorder. Now we are using instruments that have a lot more wiggle room," he said.

The CDC says it removed thimerosal from the manufacture of vaccines in 1999, but the compound was still in vaccines sold in 2003, meaning drug companies continued to sell thimerosal in vaccines until they were out of stock.

"They didn't take it out for any other reason to be nice, give me a break. You would say you would cause the vaccine manufacturers much more expense to make to appease a few parents...for something that you didn't believe in? No, they are liars. People have got to understand that they just lie to you. They are covering their rear end. It is what we call damage control," explained Dr. Haley.

"As a pediatrician I think one of the most important things we can do right after providing clean drinking water is childhood vaccines. I think the data, looking at the data, dispassionately says vaccines is not where the problem is," argued Dr. Miles.

We traveled to Springfield, Illinois to interview Dr. David Ayoub, a physician and autism researcher. He says just because vaccines don't officially contain thimerosal, trace amounts of mercury still remain. He says that trace amount is no less a problem.

"In 2004, the amount of mercury that the population has gotten has increased steadily and is still increasing. Today by the time a child turns 4, he will receive 53 percent of the peak amount of mercury he got before 1999. A 50 percent reduction is hardly an elimination. We are still getting plenty of mercury in vaccines," he explained.

Most flu vaccines, for instance, still contain 25 mcg of mercury. According to the EPA, that much mercury can only be safely processed by someone weighing 550 pounds. Babies in pregnant women receive 12.5 mcg, the EPA says that baby would have to weigh 275 pounds to process the mercury safely.

Dr. Frank Engley is a retired chairman and professor of Microbiology at the University of Missouri. He served on various committees and panels and has consulted for the CDC, NASA, the FDA, and EPA. He did some of the first research on the toxicity of thimerosal.

"We found thimerosal is toxic down to a level that is almost unbelievable. Down to 1.10, maybe 100 nanograms...a millionth of a gram and that is about as toxic as you can get," he said.

"So you can dilute it a lot and still have enough to suppress the immune system, especially if you got 2-3 vax at one time. So it is an immune system depressor. Which makes it stupid to put in vaccines," argued Dr. Haley.

Earlier in this story, we heard from Dr. Judith Miles of MU's Thompson Center. She disagrees with Dr. Haley about the dangers of thimerosal.

In our next installment we talk more with Dr. Miles about her take on the compound. Be sure to watch Wednesday at 10 for Part Two.