the "lead" weights made and sold these days are not made from lead they are a nickel alloy and safe. Lead will break down in water, rapidly, and cause lead poisioning to all aquatic life.
wow so glad you said that.. we've had a bit of bogwood in the tank for about four months now, and it had a lead weight in it to stop it from floating up we've removed it now, no signs of decomposition.. so i think all is good