Metals in the environment

Metal pollution is a widespread problem; in fact, in industrially developed countries it is normal to find elevated levels of metal ions in the environment. In addition, it has been estimated that approximately 37% of sites in the U.S. contaminated with organic pollutants, such as pesticides, are additionally polluted with metals (Kovalick, 1991). Despite this, biological treatment or bioremediation of contaminated sites has largely focused on the removal of organic compounds, and only recently has attention turned to the treatment of metal-contaminated wastes (Brierley, 1990; Summers, 1992). Due to their toxic nature, the presence of metals in organic-contaminated sites often complicates and limits the bioremediation process. Such metals include the highly toxic cations of mercury and lead, but many other metals are also of concern, including arsenic, beryllium, boron, cadmium, chromium, copper, nickel, manganese, selenium, silver, tin and zinc.

Metals are ubiquitous in nature and even those metals generally considered as pollutants are found in trace concentrations in the environment (see Table 10.1). For the most part, metal pollution problems arise when human activity either disrupts normal biogeochemical cycles or concentrates metals (see Table 10.2). Examples of such activities include mining and ore refinement, nuclear processing, and industrial manufacture of a variety of products including batteries, metal alloys, electrical components, paints, preservatives, and insecticides (Gadd, 1986; Hughes & Poole, 1989; Suzuki, Fukagawa & Takama, 1992). Metals in these products or metal wastes from manufacturing processes can exist as individual metals or more often as metal mixtures.