Definition, Objectives, and Evaluation of Natural Attenuation

Abstract

Natural attenuation offers large benefits to owners and managers of contaminated sites, but often raises strong objections from those who live and work near a site and are asked to assume most of the long-term risks. Part of the controversy comes about because published definitions of natural attenuation do not identify a realistic end-point objective, and they also are ambiguous about the naturally occurring processes that can achieve the objective. According to guidance from the U.S. National Research Council (NRC 2000), destruction and strong immobilization are the naturally occurring processes that achieve a realistic objective: containing the contaminant relatively nears its source, thereby minimizing exposure risks. The strategy for obtaining solid evidence that the objective is being achieved requires measurements that establish a cause-and-effect relationship between contaminant loss and a destruction or strong-immobilization reaction. The cause-and-effect relationship is best documented with reaction footprints, which typically are concentration changes in reactants or products of the destruction or immobilization reaction. MTBE presents a contemporary example in which footprint evidence for biodegradation is especially crucial, since aerobic biodegradation of MTBE requires special conditions not present at all sites: a high availability of dissolved oxygen and bacteria expressing particular oxygenase enzymes.

Characterization and remediation of soils contaminated with uranium

“…The monitoring of the process involves the study of the rate and extent of irreversible adsorption of uranium, the fraction of uranium in aquifers associated with the phenomenon, and the degree of irreversible adsorption of uranium required to reduce the amount of uranium under the safety levels [179,180]. Microorganisms appear to be excellent indicators of soil health because they respond to changes in the soil ecosystem quickly [181].…”

Potential use of Erica andevalensis and Erica australis in phytoremediation of sulphide mine environments: São Domingos, Portugal

“…Therefore, the phytostabilisation technique, by using specific tolerant plants with or without the application of soil amendments, could be a promising strategy for this abandoned mining area. The objective of phytostabilisation, a non-expensive and non-disruptive technique to the landscape, is not to remove contaminant elements from a site but rather to stabilise them and reduce the risk to human health and the environment (Wong, 2003;Rittmann, 2004;Adriano et al, 2004;Clemente et al, 2006), hence the importance of appropriate vegetation. The acidic soils of São Domingos (pH ≤ 4.5), highly contaminated by trace elements, began to be colonized by some plants species that seem to be adapted to such extreme environmental conditions.…”

“…The benefits of phytoremediation are quite obvious as it is non-expensive and non-disruptive to the landscape and to those living near the contaminated site (Rittmann, 2004;Adriano et al, 2004).…”

Interaction Effects of Plants and Indigenous Micro-organisms on Degradation of N-Alkanes in Crude Oil Contaminated Agricultural Soil

“…According to the Environmental Protection Agency in the United States [4] NA or intrinsic bioremediation processes include a variety of physical, chemical, and biological processes that act to reduce the mass, toxicity, mobility, volume, or concentration of contaminants. These processes include aerobic and anaerobic biodegradation, dispersion, dilution, sorption, volatilization, radioactive decay, and chemical or biological stabilization, transformation, or destruction of contaminants [5].…”