A report released this month by California's Office of Environmental Health Hazard Assessment indicates Gallium Arsenide has now been listed as a carcinogen. Given the increasing usage of gallium arsenide, the main constituent in LEDs, and their recent championing as more efficient light sources in recent news stories and Slashdot, there may be significant environmental concerns as related to their disposal. Morover, workers in industries using the substance may be at risk of cancer as well.
The radioactive decay products of Californium include Liberelium and a heavy isotope of Governmentium called Bigovernmentium, which when combined are known to be toxic.