Bioavailability and Biodegradation of Polycyclic Aromatic Hydrocarbons

多环芳烃（PAH）是超级基金站点关注的十大污染物之一，是超级基金项目管辖范围外估计45，000个站点的主要污染物。美国环保署规定了16种多环芳烃，其中7种被认为是人类致癌物。多环芳烃本身是可生物降解的，但在多环芳烃污染系统的生物修复过程中，每种EPA调节的多环芳烃的一个重要部分通常不会被去除。特别令人关注的是，4-，5-和6-环化合物，其中包括所有的致癌多环芳烃，被去除的程度低于低分子量的化合物。在现场污染土壤中的多环芳烃生物降解的限制通常归因于多环芳烃的微生物的可用性的限制，但这是很少记录在特定地点的基础上，并已被证明是不真实的5-和6-环多环芳烃在一些情况下。我们的能力，阐明在任何领域污染的系统中的PAH降解的影响因素受到限制的压倒性的复杂性的系统和我们相对有限的知识，微生物的PAH代谢和PAH降解微生物的多样性。在某些情况下，旨在改善PAH的干预措施 生物降解可导致PAH通过微生物转化的有毒副产物的形成。我们建议使用两个实验平台与现场污染土壤的多环芳烃的生物利用度，生物降解，形成有毒的生物转化产物，和净风险降低之间的关系进行调查。土柱系统将用于评价就地生物补救办法，浆相生物反应器将用于研究地上生物补救办法。我们假设，不同的微生物群落将被选择在这些系统中，导致差异的能力，以消除最生物可利用的部分的多环芳烃和形成有毒副产品的倾向。我们也 假设为改善生物降解而提出的提高PAH生物利用度的方法可能形成遗传毒性产物。多环芳烃生物降解的微生物生态学知识将扩大使用一种新兴的培养独立的分子工具（稳定同位素探测），以确定微生物负责降解相关的，复杂的系统中的多环芳烃的范围。这些知识对于最终能够评估土著微生物群落降解污染环境中特定多环芳烃的潜力非常重要。由于皮肤接触是受污染土壤中多环芳烃的主要接触途径，我们还将与项目4合作，调查受污染土壤对皮肤接触终点的影响。初步实验将量化多环芳烃的生物可利用部分相关 此外，还将评估土壤生物处理对皮肤接触的影响。

Polycyclic aromatic hydrocarbons (PAHs) are among the top 10 contaminants of concern at Superfund sites and are the major contaminants at an estimated 45,000 sites outside the jurisdiction of the Superfund program. The U.S. EPA regulates 16 PAHs, 7 of which are considered to be human carcinogens. PAHs are inherently biodegradable, but a significant fraction of each of the EPA-regulated PAHs is usually not removed during bioremediation of PAH-contaminated systems. Of particular concern is that the 4-, 5- and 6- ring compounds, which include all of the carcinogenic PAHs, are removed less extensively than the lower-molecular-weight compounds. Limitations in PAH biodegradation in field-contaminated soils are typically attributed to limitations in the availability of the PAHs to microorganisms, but this is rarely documented on a site-specific basis and has proven to be untrue of the 5- and 6-ring PAHs in a number of cases. Our ability to elucidate the factors that influence PAH degradation in any field-contaminated system is constrained by the overwhelming complexity of the system and by our relatively limited knowledge of microbial PAH metabolism and the diversity of PAH-degrading microorganisms. In some cases, interventions intended to improve PAH biodegradation can lead to the formation of toxic byproducts of PAH transformation by microorganisms. We propose to investigate the relationships among PAH bioavailability, biodegradation, the formation of toxic biotransformation products, and net risk reduction using two experimental platforms with field-contaminated soil. Soil column systems will be used to evaluate in situ approaches to bioremediation, and slurry-phase bioreactors will be used to study above-ground approaches to bioremediation. We hypothesize that different microbial communities will be selected in these systems, leading to differences in the ability to remove the most bioavailable fractions of the PAHs and in the propensity to form toxic byproducts. We also hypothesize that methods proposed to enhance PAH bioavailability for improved biodegradation are likely to form genotoxic products. Knowledge of the microbial ecology of PAH biodegradation will be expanded by using an emerging cultivation-independent molecular tool (stable-isotope probing) to identify microorganisms responsible for degrading a range of PAHs in relevant, complex systems. This knowledge is important in eventually being able to assess the potential for an indigenous microbial community to degrade specific PAHs in contaminated environments. Because dermal exposure is a major route of exposure to PAHs in contaminated soil, we will also collaborate with Project 4 to investigate the effects of contaminated soil on dermal exposure endpoints. Preliminary experiments will quantify the bioavailable fractions of PAHs relevant to potential uptake by human skin, and the effects of biological treatment of the soil on dermal exposure will be evaluated.