MISSOULA, Mont. (AP) A federal prosecutor told jurors Monday that W.R. Grace & Co. knew for years that its products posed serious health hazards to residents of Libby, Mont., but the company hid the risks from workers and government regulators.

In opening statements at a major environmental crime trial, Assistant U.S. Attorney Kris McLean said the company and its executives conspired for years to keep those hazards a secret.

"The company and individual executives chose profits at the expense of people's health and chose avoiding liability over disclosing health hazards to the government," McLean told a U.S. District Court jury in Missoula. "They endangered the health of hundreds, if not thousands."

Lawyers for W.R. Grace were to present their opening statements later Monday. In court documents, the company has contended it did not conspire to conceal the health hazards.

Grace and five of its former executives are on trial on charges that from 1976 to 1990 they knowingly exposed workers to asbestos from the vermiculite mine the company once operated near Libby, in northwestern Montana. The company and some executives also are charged with hampering the federal investigation of contamination.

Lawyers for residents of the Libby area say asbestos exposure has killed more than 200 people and sickened some 2,000, and the toll is rising because the diseases can take years to appear.

McLean contended the company did its own research and learned decades ago that even low levels of asbestos in the vermiculite became dangerous when disturbed. Even so, Grace donated dangerous mine waste to Libby schools for use in building tracks for runners, he said.

McLean said Libby suffers 40 to 80 times the national average in its rate of death from asbestosis, and the lung-cancer mortality is 30 percent higher than health officials would expect the town to experience. Libby is a town of about 2,600 people in a forested valley of the Cabinet Mountains, about 100 miles northwest of Missoula.

Kevin Cassidy, a lawyer for the Justice Department in Washington, D.C., focused his opening statements on the individual executives, some of whom were in the courtroom. He said many were long aware of the dangers, but took active steps to conceal them from workers and regulators. Even when the mine was closed and the land was being sold, they did not disclose the dangers to the buyers, who included small-business people, Cassidy said.

"As a result of that concealment, people in Libby, Mont., including unsuspecting families, were put in danger," Cassidy said.

The trial is expected to last several months.

In addition to Grace, a chemical company based in Columbia, Md., the defendants include former executives Henry A. Eschenbach, Jack W. Wolter, William J. McCaig, Robert J. Bettacchi and Robert C. Walsh.

A federal indictment unsealed in February 2005 charged Grace and its former executives with violating the federal Clean Air Act and obstructing a U.S. Environmental Protection Agency investigation into the asbestos contamination.

The case stems from the vermiculite mining on Zonolite Mountain near Libby, mining that began around 1920 and continued until 1990. Vermiculite could be processed into products used for plumbing insulation, fireproofing and gardening. Zonolite brand insulation is in some 35 million homes in the United States.

The problem is that the vermiculite from the Libby mine was contaminated with naturally occurring asbestos mineral fibers, which can be inhaled and can cause mesothelioma, asbestosis and lung cancer.

Particles of the ore got into homes on the clothes of miners. Ore also was taken to processing plants in Libby, where a smokestack released up to 24,000 pounds of dust a day. Asbestos-contaminated mine tailings were used to build running tracks at local junior high and high schools, and lined an elementary school skating rink.

After news reports of health problems, the EPA in 1999 sent an emergency team to Libby to collect information about asbestos contamination. The town was declared a Superfund cleanup site in 2002

The five retired executives, who are free on recognizance, face up to 15 years in prison and fines totaling millions of dollars if they are convicted. A verdict against Grace could lead to millions in fines against the company.

Copyright 2009 The Associated Press.