Metallic and semimetallic elements that are generally highly toxic to plants and animals and that tend to accumulate in food chains are referred to collectively as heavy metals. Heavy metals include lead, mercury, cadmium, chromium, and arsenic. Additional optional information: Many metallic and semimetallic elements analyzed in environmental samples are often referred to collectively as heavy metals. For example, EPA regulation 40 CFR 258.4 refers to the following monitoring parameters as heavy metals: antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, nickel, selenium, silver, thallium, vanadium, and zinc. Note: The term heavy metals is deeply embedded in environmental usage and will doubtless continue to be used. However, some of the elements commonly called heavy metals are not heavy (e.g., beryllium) or are not true metals (e.g., arsenic). Therefore, heavy metals should be avoided whenever more precise wording can be substituted.