Project 6: Geochemical Controls on the Sorption, Bioavailability, Formation

项目总结(见说明)： 多氯二苯并二恶英和呋喃(PCDD/Fs)由于其极低的水溶解度，与土壤和沉积物颗粒有强烈和广泛的结合。吸附的PCDD/F主要分布在主要组分--类炭质材料、无定形有机物和粘土之间，并假设这些吸附剂之间的比例分布随着PCDD/F总负荷的变化而变化。由于多氯二苯并二恶英也高度抵抗分解，因此吸附是其环境命运和影响的主要决定因素。重要的是，对土壤/沉积物颗粒的吸附可能以未知的方式改变二恶英/二恶英的生物利用度和毒性，生物利用度预计是地理吸着剂特有的。主要目标是：(1)促进对这些由土壤/沉积物组成的主要地质吸附剂对PCDD/F吸附的基本了解，特别是在与环境相关的极低浓度(Pptppb)下，假设碳质物质(例如焦炭)控制土壤-水分布，(2)使用基于生理的提取液和哺乳动物模型来确定PCDD/F吸附到每种关键地质吸附剂类型上的不同生物可及性/生物可利用性，(3)检验这样的假设，即可以推断PCDD/F与单个组分地理吸附材料的吸附/解吸反应的机理知识，以预测受污染土壤/沉积物的特定地点的生物可获得性和生物有效性以及(4)评价粘土促进的二恶英和相应的前二恶英/呋喃的形成，并阐明这些反应的潜在机理。对土壤/沉积物中PCDD/F生物有效性的估计很少，而且不一致，因此，大多数暴露于环境中的PCDD/F的风险评估模型都假设100%的生物有效性，而不考虑土壤/沉积物的特性。拟议的研究结果将为(1)更机械地理解土壤/沉积物组成与土壤/沉积物中给定的PCDD/F总负荷所带来的人类和生态风险之间的关系提供基础，以及(2)理解粘土促进的PCDD/F形成的普遍性，因为这是一个持续的原位过程，导致意外的PCDD/F累积，威胁人类健康。此外，如果某些焦炭，例如作为生物燃料/固存技术故意产生的副产品产生的焦炭，被证明是有效的土壤/沉积物改良剂，以减少多氯二苯并二恶英/二恶英的生物可利用性，将会产生巨大的经济和环境效益。

PROJECT SUMMARY (See instructions): Due to their exceptionally low water solubilities polychlorinated dibenzodioxins and furans (PCDD/Fs) are strongly and extensively bound to soil and sediment particles. Sorbed PCDD/Fs are distributed among the primary component geosorbents, namely char-like carbonaceous materials, amorphous organic matter, and clays, and the fractional distribution among these geosorbents is hypothesized to change with the total PCDD/F load. Since PCDD/Fs are also highly resistant to decomposition, sorption is a primary determinant of their environmental fates and impacts. Importantly, sorption to soil/sediment particles may modify the bioavailabilities and toxicities of PCDD/Fs in unknown ways, and bioavailability is expected to be geosorbent-specific. The major goals are: (1) to advance fundamental understanding of PCDD/F sorption by these dominant geosorbents comprising soils/sediments, especially at very low environmentally relevant (pptppb) concentrations where carbonaceous materials (e.g. chars) are hypothesized to control soil-water distribution, (2) to determine the differential bioaccessibilities/bioavailabilities of PCDD/Fs sorbed to each key geosorbent type using physiologically based extraction fluid, and mammalian models, (3) to test the hypothesis that mechanistic knowledge of sorption/desorption reactions for PCDD/Fs with individual component geosorbents can be extrapolated to predict site-specific bioaccessibilites and bioavailabilities for contaminated whole soils/sediments, and (4) to evaluate the clay-facilitated formation of PCDD/Fs, and corresponding predioxins/furans, from precursor chlorophenols, and elucidate the underlying mechanistic basis for these reactions. Estimates of PCDD/F bioavailability in soils/sediments are few and inconsistent, hence most risk assessment models for exposure to environmental PCDD/Fs make generic assumptions of 100% bioavailability, irrespective of soil/sediment characteristics. The results of the proposed research will provide the basis for (1) a more mechanistic understanding of the relationship between soil/sediment composition and the human and ecological risks posed by a given total PCDD/F load in soil/sediment, and (2) understanding the prevalence of clay-facilitated PCDD/F formation as an on-going in-situ process leading to unexpected PCDD/F accumulations that threaten human health. Further, it would be of great economic and environmental benefit if certain chars, such as those produced as intentional by-products of biofuels/Csequestration technologies, were shown to be effective as soil/sediment amendments to diminish bioavailability of PCDD/Fs.