University of Texas study draws link 
between mercury releases and autism 

SAN ANTONIO, TX (03/22/05) -- A study released by the University of Texas Health Science Center at San Antonio shows a significant increase in the rates of special education students and autism rates associated with increases in environmentally released mercury.

According to the study, on average, for each 1000 lb of environmentally released mercury there was a 43% increase in the rate of special education services and a 61% increase in the rate of autism. The association between environmentally released mercury and special education rates were fully mediated by increased autism rates. This ecological study suggests the need for further research regarding the association between environmentally released mercury and developmental disorders such as autism. These results have implications for policy planning and cost analysis. 

The study compared mercury totals reported for 2001 in the 254 Texas counties to the rate of autism and special education services in nearly 1,200 Texas school districts. The districts, which range from urban to small metro to rural, enroll 4 million Texas children. 

"The main finding is that for every 1,000 pounds of environmentally released mercury, we saw a 17 percent increase in autism rates," said lead author Raymond F. Palmer, Ph.D., associate professor in the Health Science Center's department of family and community medicine. 

Large-scale mercury exposures such as accidental spills long have been implicated with developmental disabilities, but this study is among the first to examine the relationship between potentially chronic, low-dose mercury exposure and a developmental disorder such as autism, Dr. Palmer said. 

Using statistical modeling, the researchers showed that increases in the rate of special education services were associated with higher mercury release levels. However, "it is the increase in autism that explains this relationship" in Texas, Dr. Palmer said. 

The authors cautioned that the study is an ecological investigation based on county level and school district data. This type of study does not lend itself to interpretation at the level of the individual. This is only a first step in identifying areas for further investigation. The study also does not assess changes in mercury levels over time as a predictor of rates of change in developmental disorders. While the current study precludes causal interpretation, the team is working on a second report that will investigate the longitudinal association between mercury and autism rates. 

The study authors note that the new research "has implications for toxic substance regulation and prevention policies. The effects of differing state policies regarding toxic release of mercury on the incidence of developmental disorders should be investigated." 

The study is published in the peer-reviewed journal Health & Place.