"It's destruction of our environment," Milner said.

Navy spokeswoman Karen Sellers said the uranium was fully encased inside the ammunition to protect military personnel who handled and stored it.

She added that the Navy was switching to tungsten rounds but did not provide further details.

Sellers said she could not say if depleted uranium shells were used farther north off Canada's coast during exercises in conjunction with Canadian forces.

A Canadian military spokesman said Canada's Navy had stopped using the shells.

The U.S. military used depleted uranium weapons in the 1991 Gulf War and again during fighting in Kosovo and Bosnia.

Navy officials "have told me that DU is 40 percent less radioactive than naturally occurring uranium found in sea water," Sellers told Reuters by telephone.

"The DU rounds dissolve so slowly that they would not contribute to naturally occurring (radiation) levels ... and do not pose a significant risk."

But Milner and other critics call depleted uranium highly toxic. Last year Britain's Royal Society of scientists said hundreds of soldiers in the Gulf and the Balkans could have inhaled enough toxic dust to cause health problems.

Douglas Rokke, a former U.S. Army health physicist assigned to monitor the effects of depleted uranium battlefield use, accused the Pentagon of not providing adequate medical treatment and testing for soldiers exposed to the substance, or for himself.

"These individual rounds are solid chunks of uranium. You can't hold them in your hand. It's too dangerous," he said by telephone.