Heavy Metals


Home Environmental Microbiology Thiobacillus Sludge ISO 14000 Miscellaneus Glossary Links About the author Guestbook - View - Sign Exit website		Although widely used the term "Heavy metals" does not have a certain definition, varying according to science branches. When asking a toxicologist about it we probably will obtain an aswer emphasising the chemical elements that are toxic to mammals (Zootoxicity). For an agronomist the emphasis will probably be given to chemical elements that are toxic to the plants (fitotoxicity). A chemist could emphasise chemical elements whose density is greater than 6g cm-3. The common idea of these areas mentioned about Heavy metals is that heavy metals are metals or metaloids associated with polution and toxicity. More recently many studies showed that some of these "toxic" elements play an important role in many metabolic pathways of animals and plants (Co, Cu Mn, Se e Zn), but only if absorbed in minimal concentrations (ppm - parts per million, or ppb - parts per billion). Above these limits they are toxic. A diet complemented with chromium, for example has an important role in preventing the developing of diabetes.

Maximum concentration of heavy metals permitted in sludges (mg/kg) for agricultural use (WEBBER, 1983)