WASHINGTON, May 5 (UPI) -- A new study has found a possible link between higher mercury emissions and higher rates of autism.
The study, accepted for publication in the peer-reviewed journal Health and Place, looked for an association in Texas between rates of autism, special education services and levels of mercury released into the environment.
"There was a significant increase," according to the study. "On average, for each 1,000 pounds of environmentally released mercury, there was a 43 percent increase in the rate of special education services and a 61 percent increase in the rate of autism."
The Bush administration is announcing a new proposal to control mercury emissions that has already stirred controversy.
The study's lead author, Raymond F. Palmer, an associate professor at the University of Texas Health Science Center in San Antonio, cautioned the findings are limited, but added they should prompt more research. The following is a transcript of an interview United Press International conducted with last March:
Q. Will you describe the study in layman's terms?
A. I think it's the first study to look at total legal amounts of released mercury from different sources of industry, and it's a relationship between that and developmental disorders and special education rates at the general population level.
Q. Also, autism has really not been looked at as part of this picture of mercury in the environment.
A. Right, it's the first one to look at autism in relationship with it. Now this is only an associational study, and there are some limits to this study, but it's a good starting point to look at this issue -- a first jumping-off point where you could say there's an association here.
There's a hypothesis that mercury is associated with autism. This just supports that general hypothesis, but it in no way confirms it -- the findings that higher emissions of mercury are related to higher rates of autism.
Q. When you say there's a hypothesis, are you referring to thimerosal (the ethyl mercury preservative that was used in childhood vaccines through the 1990s)?
A. Right. And that's mercury. That's just another form of mercury.
Q. Now what critics would say is that there is no evidence that ethyl mercury in vaccines can do that kind of damage. Whereas environmental mercury is a different kind entirely and has known toxic effects on humans.
A. That gap is starting to close because there are some studies starting to show that ethyl (mercury in thimerosal) is as toxic.
I think what the critics would say is this (study) is an ecological association, it's cross-sectional, meaning it's at a point in time. And then being ecological, you cannot infer anything at the individual level. So anybody who really wants to rip into this can.
But if you have a hunch about a relationship as serious as this and you go investigating it and (find an association) at this level, it gives you confidence to move on to the next level.
Q. What would the next level be?
A. You'd want maybe to look at the association over time. We have some data on that, too, and that's our next step. We're working on that paper right now -- levels of mercury related with a change in autism over time, not just the prevalence rate at one specific point.
Q. I understand you've also looked for an association between mercury emissions and autism at the national level?
A. That's an unpublished manuscript. But the data that I have at the states level, the 50 states, is consistent with the same idea. States that are reporting the highest levels of mercury emissions also have the highest rates of developmental disorders including autism. I'm still trying to get that one published.
Q. New mercury-emissions standards are being announced by the Bush administration. Some people say they don't go far enough. Does your study have implications for this issue?
A. I would say that it does suggest that further study has to be done. Nobody really knows the long-term effects of low-dose mercury exposure. I would think this is a serious enough issue that we would want politicians to look at it, given that the substance is such a toxic element.
Q. I understand that in doing your study you came across a possible correlation between autism rates and an old mercury mine?
A. We were also mapping this relationship in counties of Texas, and we identified the counties with the highest levels of autism and the highest mercury rates.
One county that stood out, Brewster County, didn't have very much mercury reported to the TRI (Toxic Release Inventory Program of the Environmental Protection Agency). But it did have high autism rates.
So we were wondering about that and found that they had historically been one of the top mercury mines in the nation.
Q. How could an old mercury mine have any effect on autism rates?
A. (Perhaps because) it just stays in the environment forever. We don't know.
The other thing about the study, the criticism, is that we're just inferring exposure because of the release (of mercury emissions). So again it's hard to say that there's individual-level exposure. We're talking about potential for exposure.
I think it's an important study to lend support to further investigation. Why not? Why not investigate it more? What do we have to lose?
Q. Does that apply to the mercury in vaccines as well? The Institute of Medicine has rejected that idea and said research money should be spent in more promising areas.
A. I think if you look at everything in (terms of) total toxic load, thimerosal could just be another source. If you have it in your environment, and you're also getting it in, say, you're mother's diet, and fish, and also through your immunization schedule, that's just one source. And the environmentally released mercury is also just one source.
Q. Could other heavy metals be playing a role here?
A. There are some studies showing that other pollutants could potentiate the action of mercury. Like aluminum, like PCBs, pesticides. The point is, we're at this stage of investigation where nobody really knows.
This article is the fifth of seven in a series UPI published earlier this year.
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