About 6 out of every 100,000 employed adults had lead poisoning in 2009, down from 14 per 100,000 in 1994.
"It's definitely good news. It dropped by over 50 percent," said one of the study's authors, Dr. Geoff Calvert of the Centers for Disease Control and Prevention.
Lead poisoning in adults is almost always due to at-work exposures. CDC officials say the decline may be tied to a reduction in the number of manufacturing jobs that involve lead, lead paint or lead dust.
One example: Employment in the lead and zinc ore mining industry dropped from more than 2,200 in 2001 to 1,666 in 2009, according to U.S. Bureau of Labor Statistics data.
Improved conditions in factories or at construction sites where lead is found may be another explanation, said Calvert, who leads a CDC team that monitors workplace illnesses.
Lead is a metal that can harm the brain, kidneys and other organs. For years it was used in gasoline and paint. Children are especially susceptible, and there is a much lower threshold in blood lead levels for a child to be diagnosed with lead poisoning.
The new report is based on adults who had been to the doctor and were found to have lead amounts in their blood that are high enough to cause at least some symptoms, such as irritability and concentration problems.
CDC researchers looked at 1994, the first year for which data was available, and 2009, the most recent year. Not all states reported data, but the results are believed to be nationally representative, Calvert said.
Although the national average in 2009 was 6 cases of lead poisoning per 100,000 adults, the rate was at or above 20 per 100,000 in Pennsylvania, Missouri and Kansas.
The types of industry in those states are believed to be an explanation. For example, Missouri is a traditional home of lead mining. Kansas produces lead-using storage batteries, like the kinds used in automobiles.
The research is being published this week in a CDC publication, Morbidity and Mortality Weekly Report.
The CDC report: http://www.cdc.gov/mmwr