Mercury exposure in the United States increases with age, then starts tapering off when people turn 50, the Centers for Disease Control and Prevention found in a study released today.

The CDC study is the first to measure mercury exposure in a wider U.S. population, following research that focused on young children and women in their childbearing years. People are often exposed to mercury through contaminated seafood, and a recent U.S. EPA survey found that almost half of U.S. freshwater fish carry mercury in excess of federal safe levels for human consumption.

The CDC data are part of a project assessing chemicals in people's bodies. The agency has added 75 contaminants to its database, bringing the total to 212 chemicals.

The survey analyzed blood, serum and urine samples from 2,500 people as a part of the CDC's National Health and Nutrition Examination Survey, which is released every two years.

The goal of the research is to determine which chemicals end up in people's bodies and at what concentrations. It is meant to help prioritize scientific work and for policymaking. Scientists chose which chemicals to look for based on expected widespread exposure and known toxicity.

Among the report's findings:

• Perchlorate was detected for the first time in all participants. Perchlorate is a naturally occurring salt that is also a component of rocket fuel and fireworks. High levels of perchlorate are known to affect thyroid function, while the health effects of low-level exposure are being debated.

• Bisphenol A, or BPA, was found in more than 90 percent of the participants' urine. BPA is an industrial chemical that mimics estrogen and has been shown to cause developmental problems and precancerous growth in animals.

• Lead exposure has been decreasing since the 1970s, validating public health efforts to reduce childhood exposure, the report says. Between 1999 and 2004, 1.4 percent of young children had elevated blood lead levels, the smallest percentage of any of the prior survey periods. But the health of high-risk children -- those living around lead-based paint or lead dust -- remains a concern.

• Acrylamide -- formed when foods containing carbohydrates are cooked at high temperatures -- was detected for the first time and is common in the U.S. population.

Biomonitoring detects a chemical's presence only and cannot evaluate whether its detection signals adverse effects or disease, the report cautions. Many environmental public health advocates say the findings play a critical first step in prioritizing the thousands of chemicals currently in the market today, many of which have little safety data publicly available.

"Biomonitoring studies such as the ones conducted by the CDC provide direct evidence that people are being exposed to harmful chemicals without their knowledge, much less their consent," said Davis Baltz, a senior associate with Commonweal, a nonprofit. "This is critical information for decision-makers, who can then craft policy instruments that will reduce or prevent exposures and also have a way to track whether those instruments are working."

Sen. Frank Lautenberg (D-N.J.), said in a statement that CDC's findings highlight the need to reform the Toxic Substances Control Act (TSCA), the law governing all industrial chemicals on the marketplace.

"Far too little is known about the hundreds of chemicals that end up in our bodies, and EPA has far too little authority to deal with the chemicals that science has already proven dangerous," Lautenberg said.

Lautenberg said he plans to introduce legislation to reform TSCA early next year that would require that EPA determine whether chemicals meet new safety standards based on scientific risk assessment and that chemical companies provide enough data to make that determination. Lautenberg also wants EPA to prioritize taking action on chemicals that present the greatest health risk.

Click here to read the study.