Inmates and employees at 10 federal prisons were exposed to toxic metals and other hazardous substances while processing electronic waste for recycling, a four-year investigation by the Justice Department’s inspector general found.

A report issued last week by the Office of the Inspector General said unspecified amounts of that waste were shipped overseas, possibly to undeveloped countries. Reports have multiplied in recent years that electronic waste is being dumped in developing nations, where it can harm local populations by leaching into groundwater or attracting scavengers who are exposed to toxic elements.

Despite the finding of exposure, however, the inspector general, Glenn A. Fine, said he could link no health problems to the recycling work in the prisons, although he did not rule out that a link could be established in the future.

That did little to assure critics of such prison-based programs.

“We have said all along that prisoners should not be managing toxic waste, and the federal government should never allow the export of such wastes to developing countries,” said Jim Puckett, executive director of the Basel Action Network, a group that advocates for rigorous standards for recycling electronic waste.