Cannabis collects heavy metals. It “absorbs heavy metals from the soil, water and air,” says Bob Clifford, general manager at Shimadzu Scientific Instruments. These elements—arsenic, cadmium, lead, mercury and others—can trigger a range of health problems, including cancer and heart disease. Although cannabis for human consumption or smoking should be as free from heavy metal contamination as possible, that’s not always the case. When Sammy Hagar wrote “sparks fly in the middle of the night,” little did he know that this line could describe not just heavy-metal music, but the concerns of testing of cannabis for these elements.