Chicago ? Lead is the No. 1 environmental health hazard for children, but a new study indicates that more than 30 million American adults may be at risk of premature death because of past exposure to the metal.

The study, reported in the current issue of the Archives of Internal Medicine, found that people who had elevated blood levels of lead early in life have a 46 percent increased rate of mortality from all causes later on, indicating that children may carry a legacy of lead toxicity as they grow older.

Children are especially vulnerable to lead’s effects, and it has long been known that lead can cause mental retardation in those exposed to relatively modest levels. But once children reached adulthood it was thought they would be more resistant to the damage.

Experts say the findings not only underscore the importance of enforcing laws regulating the removal of lead paint from older houses, where children can ingest lead in dust and paint chips, but also suggest that federal standards for the amount of lead adult workers can have in their blood may be set dangerously high.

Lead’s danger to children led to the gradual elimination of leaded gasoline and lead paint, the two major sources of lead in the environment. Lead was banned from residential paint in 1978, and leaded gasoline was phased out by 1986. Blood lead levels have since plummeted dramatically.

But for people in their late 30s and older who were exposed to much higher levels of lead before the bans, the heavy metal now poses a serious threat to their lives, said Ellen Silbergeld of Johns Hopkins University, who headed the study.

Her findings show people who had elevated blood lead levels — although still below those currently considered safe in industry — had a significantly higher rate of death, especially from heart disease, than people who had much lower blood levels.