Bioavailability (the availability to biota) of organic contaminants is a critical issue for DOD installation restoration programs. Reduced availability of contaminants to biodegrading microbial populations frequently is a rate limiting problem in site cleanup of soils, groundwater, and freshwater and marine sediments. Contaminants may interact with soil and sediment particles to create complex residues which are protected from attack by microbial enzymes. Chemical solubility and sorption to surfaces of clay or colloidal organic matter may also alter the availability of contaminants to microorganisms. Mass transfer limitations (e.g., pore diffusion) may limit the rate of biodegradation and hence bioavailability. Slow leaching of contaminants from soils has been a problem in site which have been remediated. Furthermore, physical characteristics of the soil or sediment system may limit transport of bacteria with biodegradation capabilities to the contaminant sites within the porous media.

Bioavailability refers to the extent to which humans and ecological receptors are exposed to contaminants in soil or sediment. The concept of bioavailability has recently piqued the interest of the hazardous waste industry as an important consideration in deciding how much waste to clean up. The rationale is that if contaminants in soil and sediment are not bioavailable, then more contaminant mass can be left in place without creating additional risk. A new NRC report notes that the potential for the consideration of bioavailability to influence decision-making is greatest where certain chemical, environmental, and regulatory factors align. The current use of bioavailability in risk assessment and hazardous waste cleanup regulations is demystified, and acceptable tools and models for bioavailability assessment are discussed and ranked according to seven criteria. Finally, the intimate link between bioavailability and bioremediation is explored. The report concludes with suggestions for moving bioavailability forward in the regulatory arena for both soil and sediment cleanup.

The presence of trace organic chemicals (TOrCs) in municipal biosolids in the U.S. has received considerable attention by the public and scientific community over the last several years. Of particular concern is whether the presence of TOrCs in biosolids results in significant risks to public health and the environment upon land application of the biosolids. While the U.S. Environmental Protection Agency has evaluated the risks associated with dioxins present in biosolids-amended soils, to date, no other TOrCs, particularly those of emerging concern, have been subjected to complete risk assessments with respect to the land application of municipal biosolids. This study identified the scientific data gaps that should be filled if appropriate risk assessments are to be conducted. The focus of this effort was to compile data from published peer-reviewed literature that addresses the occurrence, mobility, persistence, bioaccumulation, toxicity, and microbial impacts of biosolids-borne TOrCs in soils. In addition, an evaluation of the current modeling approaches employed to evaluate the risks of biosolids-borne TOrCs was conducted.