Health agencies should increase awareness about exposure to asbestos in Montana vermiculite processed years ago at locations around the country, a federal agency said Wednesday in a report about the study of 28 sites that received the vermiculite.

Increased awareness is important for people who had significant exposure to asbestos, for health care providers and for public health and environmental professionals, the Agency for Toxic Substances and Disease Registry said.

Health agencies should continue providing education materials to people who were exposed, ATSDR said. In addition, information about asbestos-containing vermiculite should be included in occupational and environmental literature, and people exposed should be encouraged to discuss their situation with health care providers.

The Libby mine that supplied vermiculite to the 28 sites and many others opened in the 1920s and closed in 1990. Since the closure as a W.R. Grace & Co. operation, asbestos has been blamed for disease and dozens of deaths in Libby. ATSDR reported in 2002 that Libby mortality rates from lung-scarring asbestosis were 40 to 80 times higher than expected, and that lung cancer deaths surpassed expectations by 20 percent to 30 percent. Most asbestosis cases involved former employees of the mine and processing facilities, or members of the employees' households.

Asbestos exposure is linked to noncancerous respiratory disease and to lung cancer, but ATSDR said exposure does not always bring health problems.

Study of the sites focused on potential pathways of exposure to asbestos through Libby vermiculite, which was used in insulation and gardening. At 27 of the sites, an exfoliation process used heat to expand the vermiculite into accordion-like nuggets. The heat released asbestos fibers into the air, where they could be inhaled.

''We are not at all suggesting that there needs to be immediate action at these sites,'' said Barbara Anderson, an environmental health scientist at ATSDR in Atlanta.

The other site on the list of 28 used vermiculite to manufacture of gypsum board.

Further investigation at sites where exfoliation did not occur appears unwarranted, ATSDR said.

Workers at the exfoliation sites, their families and people living close by may have been exposed to asbestos, ATSDR said in the report identifying groups of people most at risk of exposure.

As ATSDR studied the 28 sites between 2002 and 2007, it released site-specific reports, information compiled in the report posted Wednesday on the Internet. Investigators have identified 78 other sites that ''may deserve a look,'' Anderson said.

''While the number of people who were exposed to this asbestos is relatively low, ATSDR and our public health department partners are concerned about the health effects of this substance on the people who worked and lived around these facilities when they actively processed vermiculite from the Libby mine,'' William Cibulas of ATSDR said in a statement.

''The information we have developed and shared will help these people better understand the potential risks for exposure and what to do if they feel they have been exposed,'' said Cibulas, director of ATSDR's Division of Health Assessment and Consultation. He said most people living or working around the sites today are not exposed to Libby asbestos.

The U.S. Environmental Protection Agency requested evaluation of Libby-related vermiculite sites, and ATSDR selected the 28 from an EPA list. Before the Libby mine closed, it supplied vermiculite to several hundred places in the United States.

Residual asbestos probably remains in indoor dust at former exfoliation sites and in exterior soil, said ATSDR, which recommends re-evaluation of data for those places, many still in use for commercial and industrial operations.

The 28 sites are in Easthampton, Mass.; Edgewater, N.J.; Hamilton Township, N.J.; Weedsport, N.Y.; Beltsville, Md.; Ellwood City, Pa.; New Castle, Pa.; Tampa, Fla.; Wilder, Ky.; West Chicago, Ill.; Dearborn, Mich.; Minneapolis; Marysville, Ohio; New Orleans; Dallas; St. Louis; Omaha, Neb.; Denver; Minot, N.D.; Glendale, Ariz.; Phoenix; Glendale, Calif.; Newark, Calif.; Santa Ana, Calif.; Honolulu; Portland, Ore. (two sites); Spokane, Wash.

On the Net:

Toxic Substances and Disease Registry: www.atsdr.cdc.gov/asbestos/sites/national--map