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

项目总结（见说明）： 由于多氯二苯并二恶英和多氯二苯并呋喃的水溶性极低，它们广泛而牢固地附着在土壤和沉积物颗粒上。吸附的二恶英/Fs之间的主要组成部分geosorbents，即炭状含碳材料，无定形有机物，粘土，和这些geosorbents之间的分数分布被假设为改变与总的二恶英/F负载。由于多氯二苯并对二恶英和多氯二苯并呋喃也具有很强的抗分解性，因此吸附作用是其环境归宿和影响的主要决定因素。重要的是，土壤/沉积物颗粒的吸附作用可能会以未知的方式改变多氯二苯并对二恶英和多氯二苯并呋喃的生物利用率和毒性，预计生物利用率将因地吸附剂而异。主要目标是：（1）促进对这些主要的土壤/沉积物地质吸附剂吸附多氯二苯并对二恶英和多氯二苯并呋喃的基本认识，特别是在碳质材料（2）使用生理提取液确定吸附到每种关键地质吸附剂类型上的PCDD/Fs的不同生物可获得性/生物有效性，和哺乳动物模型，（3）检验以下假设：多氯二苯并对二恶英和多氯二苯并呋喃与各成分地质吸附剂的吸附/解吸反应的机理知识可以外推，以预测受污染的整个土壤/沉积物的特定地点的生物可及性和生物可利用性，以及（4）评估粘土促进多氯二苯并对二恶英和多氯二苯并呋喃以及相应的前二恶英/呋喃从前体氯酚形成的情况，并阐明了这些反应的潜在机理基础。对土壤/沉积物中多氯二苯并对二恶英/多氯二苯并呋喃生物利用度的估计很少，而且不一致，因此，大多数关于接触环境中多氯二苯并对二恶英/多氯二苯并呋喃的风险评估模型都作出100%生物利用度的一般性假设，而不管土壤/沉积物的特性如何。拟议研究的结果将为以下两方面提供基础：（1）更机械地了解土壤/沉积物成分与土壤/沉积物中给定的多氯二苯并对二恶英/多氯二苯并呋喃总含量对人类和生态造成的风险之间的关系;（2）了解粘土促进多氯二苯并对二恶英/多氯二苯并呋喃形成的普遍性，这是一个持续的原位过程，导致了威胁人类健康的意外多氯二苯并对二恶英/多氯二苯并呋喃积累。此外，如果某些炭，例如作为生物燃料/碳螯合技术的有意副产品生产的炭，能够有效地作为土壤/沉积物改良剂，减少多氯二苯并对二恶英/多氯二苯并呋喃的生物利用度，将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.