Bioavailability and Biodegradation of Polycyclic Aromatic Hydrocarbons

多环芳烃(PAHs)是超级基金站点最受关注的10种污染物之一，也是超级基金计划管辖范围外约45,000个站点的主要污染物。美国环保局监管16种多环芳烃，其中7种被认为是人类致癌物质。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，EPA调节的每个多环芳烃中的很大一部分通常不会被去除。尤其令人担忧的是，包括所有致癌多环芳烃在内的4-环、5-环和6环化合物比低分子量化合物去除的范围要小。农田污染土壤中多环芳烃生物降解的局限性通常归因于微生物对多环芳烃可用性的限制，但这一点很少在特定地点的基础上记录下来，而且在许多情况下被证明不适用于5环和6环多环芳烃。我们在任何受田间污染的系统中阐明影响多环芳烃降解的因素的能力受到系统的压倒性复杂性以及我们对微生物多环芳烃代谢和降解多环芳烃微生物多样性的相对有限的知识的限制。在某些情况下，旨在改善PAH的干预措施 生物降解会导致微生物转化多环芳烃产生有毒副产物。我们建议使用两个田间污染土壤的实验平台来研究多环芳烃的生物有效性、生物降解性、有毒生物转化产物的形成和净风险降低之间的关系。土柱系统将用于就地评估生物修复的方法，而泥浆相生物反应器将用于研究地上生物修复的方法。我们假设，在这些系统中将选择不同的微生物群落，导致去除多环芳烃中生物可利用程度最高的部分的能力和形成有毒副产品的倾向的差异。我们也 假设为改善生物降解性而提出的提高多环芳烃生物利用度的方法很可能形成遗传毒性产品。将通过使用一种新兴的不依赖栽培的分子工具(稳定同位素探测)来确定在相关复杂系统中负责降解一系列多环芳烃的微生物，从而扩大对多环芳烃生物降解的微生物生态学的了解。这一知识对于最终能够评估本土微生物群落在受污染环境中降解特定多环芳烃的潜力非常重要。由于皮肤暴露是接触受污染土壤中多环芳烃的主要途径，我们还将与项目4合作，调查受污染土壤对皮肤暴露终点的影响。初步实验将量化相关的多环芳烃的生物可利用部分 此外，还将评估土壤生物处理对皮肤暴露的影响。

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.