MUSKEGON, Mich. — For more than 75 years, shipping companies that haul iron ore, coal, salt and limestone have dumped their "cargo sweepings" -- residual materials and wash water left on freighters after they are unloaded -- into the Great Lakes to avoid contaminating future loads.

Despite federal laws and an international treaty that prohibit the practice, U.S. and Canadian freighters empty about 2 million pounds of cargo sweepings into the lakes each year, according to federal data.

Ships unload anywhere from a few pounds to a few thousand pounds of leftover cargo materials, but because the dumping usually takes place several miles offshore, few people outside the shipping industry know about it.

Regulators have turned a blind eye toward cargo sweeping because shipping industry officials and some scientists claim it is environmentally harmless and contend there are no viable disposal alternatives.

The Coast Guard is about to begin what is believed to be the first scientific study to determine whether the practice is harming the Great Lakes, The Muskegon Chronicle reported Tuesday.

The study could determine whether government agencies restrict the practice or ban it outright. At this time, the Coast Guard wants to permit cargo sweeping.

The shipping industry is opposed to any restrictions.

"Banning cargo sweeping would be catastrophic to the shipping industry. It would shut down power production, steel production and all kinds of construction activities in the region," said James Weakley, president of the Lake Carriers Association, a Cleveland-based trade group.

He said cargo sweepings don't contain hazardous substances.

"It's the equivalent of sweeping out my garage," Weakley said.

But Mark Coscarelli, a Lansing environmental consultant, questioned why government agencies that strive to keep pollutants out of surface waters would allow freighters to dump iron ore, coal, salt and cement dust into the world's largest source of fresh surface water.

"We have to ask ourselves if this is good public policy," said Coscarelli, who worked in Michigan's Office of the Great Lakes for more than a decade.

The federal Clean Water Act prohibits dumping waste into lakes Erie, Huron, Michigan, Ontario and Superior. So does an international shipping treaty, called MARPOL Annex V, that Congress adopted in 1990.

U.S. officials who approved MARPOL V, which banned trash dumping at sea, apparently were unaware that the treaty effectively outlawed cargo sweeping in the lakes.

Instead of banning the practice, the Coast Guard in 1993 adopted an interim exemption policy that allows it to continue virtually unregulated. The Coast Guard now wants to make that interim policy a permanent rule.

U.S. and Canadian freighters dumped 432,242 pounds of cargo sweepings in Lake Michigan in 2001, according to federal data. The biggest load that year, 680,300 pounds, was dumped in Lake Huron.

The cargo sweepings discarded in Lake Michigan in 2001 included 187,530 pounds of iron ore, 80,132 pounds of coal and 138,548 pounds of stone.

Coast Guard officials have said there is no scientific proof that the dumping hurts the Great Lakes' water quality or fish habitat.

Source: Associated Press