"We see that lead comes out at the top of the list in terms of developmental toxicants and known or suspected carcinogens," said commission spokesman Evan Lloyd.

Lead can accumulate in the human body, harming the reproductive system and causing nervous system damage in fetuses and small children, which can lead to problems with their physical and mental development. It can also cause cancer.

Lead released into the environment totaled 43.4 million kilograms in 2002, accounting for 24 percent of the total release of 77 developmental toxins in the study of data submitted to the US and Canadian governments by 24,192 facilities in 2002.

Steps taken to reduce emissions of lead, such as eliminating leaded gasoline, have drastically cut its concentrations in the environment, the report said.

In the United States, lead concentrations in the air fell by 94 percent from 1983 to 2002, but the overall problem of lead emissions has not gone away, the commission said.

"It's contained -- in a majority of these instances in terms of volume -- in a relatively few, very large metal smelters and manufacturing facilities," Lloyd said.

Canadian industrial facilities representing 5 percent of those reporting emissions of lead and its compounds accounted for 42 percent of lead releases into the air in 2002, according the the report.

The top emitter of lead on site was a base metal smelter owned by Hudson Bay Mining and Smelting in Manitoba, a company spun off last year by Anglo American Plc.

The others in the top three were Noranda Inc.'s Horne smelter in Quebec and Inco Ltd.'s Copper Cliff complex in Ontario.

"Currently in Canada, there are no limits on lead air emissions from smelters, whereas in the United States ... there are various standards applied across the board," Lloyd said.

In a statement Tuesday, Canadian Environment Minister Stephane Dion said the government is aware of the problem and last year proposed measures that would reduce lead emissions from smelters by some 30 percent by 2008.

($US1=$1.26 Canadian)