How Can Information On Oral Bioavailability Improve Human Health Risk Assessment For Lead Contaminated Soils

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.

Until the publication of this new book there had been a lack of well-founded guidelines for evaluating concentrations of lead in soil and its relationship to human health. Thus, much confusion has existed among regulatory agencies, industries, public health officials, and the medical community about the evaluation and remedying of lead-contaminated soils. Lead in Soil: Recommended Guidelines represents the combined efforts of a multi-disciplinary international task force from the Society for Environmental Geochemistry and Health (SEGH) whose members are experts in the fields of lead pollution and toxicology. It provides an international consensus concerning environmental lead and blood lead-especially in children. The task force evaluated the evidence and made recommendations for guidelines to appraise lead concentration. It also studied the influence of soil and other sources of lead on blood lead concentrations. A model was prepared that allows the user to select appropriate target levels of blood lead while allowing for a variety of environmental situations or regulatory criteria.

Until the publication of this new book there had been a lack of well-founded guidelines for evaluating concentrations of lead in soil and its relationship to human health. Thus, much confusion has existed among regulatory agencies, industries, public health officials, and the medical community about the evaluation and remedying of lead-contaminated soils. Lead in Soil: Recommended Guidelines represents the combined efforts of a multi-disciplinary international task force from the Society for Environmental Geochemistry and Health (SEGH) whose members are experts in the fields of lead pollution and toxicology. It provides an international consensus concerning environmental lead and blood lead-especially in children. The task force evaluated the evidence and made recommendations for guidelines to appraise lead concentration. It also studied the influence of soil and other sources of lead on blood lead concentrations. A model was prepared that allows the user to select appropriate target levels of blood lead while allowing for a variety of environmental situations or regulatory criteria.

Lead (Pb) speciation in soil is key for bioavailability assessment and exposure risk to humans from Pb contaminated soils. Soil ingestion is the main exposure pathway in Pb contaminated soils and in vitro bioaccessibility assays (IVBA) can predict relative bioavailable (RBA) Pb in soil by mimicking the GI tract conditions without traditional expensive animal feeding studies. In situ soil remediation has been considered an effective ecological treatment option compared to ex-situ techniques. The use of amendments such as biosolids, biochar, compost and phosphorous (P) amendments have been effective to decrease RBA in soils and, in doing so, reducing human exposure to the contaminant. In this study, soil amendments including biosolids, compost, wood-ash, biochar, soluble phosphate (SP) and their combinations were applied to Pb contaminated soil. Soil samples were incubated for up to 6 months at constant temperature, moisture and humidity. Samples were taken at three time points 1 (t1), 4 (t2) and 6 (t3) months of incubation and analyzed for total metal content, bioaccessible Pb (%IVBA-Pb), bioaccessible arsenic (%IVBA-As), organic carbon content (Org C), pH, extractable P and other key properties to determine the best treatment to reduce bioavailability of lead while improving soil health. Phosphorous was the most effective amendment to reduce %IVBA-Pb. Whether as individual or combined amendments, SP and biosolids resulted in 25-50% reductions of %IVBA Pb. Organic C addition did not reduce %IVBA-Pb, indicating complexation was not relevant for chemical immobilization of Pb in the case of strongly acidic soils such as the ones used in this experiment. %IVBA-As was correlated with pH and not P addition nor Organic C addition. Biosolid addition produced, apart from an expected plant available P increase, a great increase in Mineralizable Nitrogen content in the soils. Considering the importance of Nitrogen as an essential nutrient in plant growth, these results indicate that this amendment would be suitable for decreasing %IVBA-Pb and overall exposure to Pb contaminated soils. This is due to ensuring plant cover in the soils and decreasing soil erosion and loss, with the subsequent Pb dust dispersion, decreasing possible ingestion rates of the soil.

The Phase II objective was to provide information on the role of bioavailability in evaluating human exposures to chemicals in soil and how this scientific information can be used to enhance risk assessment and remediation decisions at soil-sites. The BPP Working Group formed a Metals Task Force and an Organics Task Force to help focus on timely developments in basic and applied science and regulatory policies for each chemical group. Emphasis was placed on providing a greater context for understanding and using bioavailability in assessing human health risks and potential remedies, as well as identifying information needs for future decision-making. Each Task Force developed similar areas for investigation and study, which are as follows: Relative Bioavailability and Risk Determination; Methods for Assessing Bioavailability from Soils; Assessment of Current Scientific Knowledge; Future Research Needs; Regulatory Policies; Case Studies; Conclusions and Future Dire.