Heavy metals are metallic elements that are present in both natural
and contaminated environments. In natural environments, they occur at low
concentrations. However at high concentrations as is the case in contaminated
environments, they result in public health impacts. The elements that are of
concern include lead, mercury, cadmium, arsenic, chromium, zinc, nickel and
copper. Heavy metals may be released into the environment from metal smelting
and refining industries, scrap metal, plastic and rubber industries, various consumer
products and from burning of waste containing these elements. On release to
the air, the elements travel for large distances and are deposited onto the soil,
vegetation and water depending on their density. Once deposited, these metals
are not degraded and persist in the environment for many years poisoning humans
through inhalation, ingestion and skin absorbtion. Acute exposure leads to nausea,
anorexia, vomiting, gastrointestinal abnormalities and dermatitis.