Toxic heavy metals are often referred to as heavy metals. In the field of environmental pollution, metals or metal-like elements with obvious toxicity to organisms are regarded as heavy metals. As metal-like arsenic has obvious toxicity to organisms, arsenic will also be listed in heavy metals. Mercury, cadmium, lead and arsenic are the main toxic heavy metals, as are other metal elements such as chromium, zinc, copper, cobalt, nickel, tin and silver, which are not easily degraded by microbes.