Advances in Bioremediation of Toxic Heavy Metals and Radionuclides in Contaminated Soil and Aquatic Systems

Abstract

Metals are used in several products essential to humans. However, processes for extraction of the metals generate effluents containing chemical by-products many of which are toxic to living organisms and are disruptive to ecosystems. Processes used in the creation of useful products from the metals leave a legacy of pollution that may take generations to clear. Metals such as mercury, cadmium, lead, chromium, and uranium, and a range of metalloids such as arsenic and selenium, are widely known for their acute toxicity at high doses and carcinogenicity at low doses. Several technologies for treatment of land and water that have been contaminated with toxic heavy metals have been proposed. Other metallic elements, although possessing no significant chemical toxicity to organisms, occur as radioactive isotopes that impart oxidative stress on organisms leading to increased incidence of mutations and carcinomas in animal tissue. The main difficulty in the treatment of metals is that the metals cannot be degraded or mineralized as is the case with organic pollutants. Metallic elements can only be oxidized or reduced to forms that are less mobile and easier to extract from the environment. This chapter is compiled from information from projects in which metals were either oxidized or reduced to less mobile and less toxic states using pure or consortium cultures of bacteria followed by immobilization or extraction using physical or biological media. The uptake of metals for reuse was attempted using bioengineered molecular adsorbents on cell surfaces. The latter process was developed to facilitate selective uptake of different metallic species as a low energy biorefinery.