Organic compounds in sludge-amended soils and their potential for uptake by crop plants

Numerous toxic organic chemicals (TOs), with a wide range of chemical properties, can occur in sewage sludges. The vast majority of sludge-borne TOs occur at low concentrations, and even lower TO concentrations are expected in sludge-amended soils. Further, most TOs are so strongly reactive in the soil-sludge matrix that their bioavailabilities to plants are expected to be low. A host of experimental techniques have been employed to measure TO plant uptake and to relate bioavailability to TO chemical and physical properties. The strengths and weaknesses of several experimental approaches are examined, and the resulting data are evaluated. Sound experimental data, especially field data and/or data from studies with endogenously sludge-borne TOs, indicate negligible contamination of crop plants with TOs in sludge-amended soils. Assessing the potential for plant uptake of sludge-borne TOs involves determining: (a) which TOs are most likely present in biosolids and what are their toxicities; (b) what quantities of TOs are likely to be added to the growth media via biosolids application; (c) what effects various dissipation/dispersion reactions have on the potential bioavailability of TOs; and (d) what are the various mechanisms for plant uptake/metabolism of TOs.