Toxicology is the science of poisons, which are sometimes referred to as toxins or toxicants. The earlier term applies to all natural poisons produced by organisms, such as the botulinum toxin produced by the bacteria Clostridium botulinum. Heavy metals are metallic chemical elements that have a relatively high density and are toxic or poisonous at low concentrations. Examples are mercury, lead, nickel, arsenic and cadmium. Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation.
Pollution and toxicology is an inter-disciplinary field of science concerned with the investigation of the destructive impacts of various substance, organic and physical entities on living life forms. Pesticides are termed as one among the major source of ecological pollution and toxicity, as these are chemically synthesized agents that have been known to persist in the environment long after their administration.