Biodegradation of high molecular weight PAHs in contaminated soil

多环芳烃(PAH)是美国许多地点土壤和地下水中的主要污染物。许多PAH是已知或疑似致癌物质，但许多也已知可被本土和受污染土壤中的细菌和真菌生物降解。生物过程已被用来修复多环芳烃污染的场所，但高分子量致癌物质的去除往往是不完整的。由于这些化合物在水中很难溶解，它们在污染系统中对某些多环芳烃的生物降解受到生物利用度以外的其他因素的限制。这个项目的目的是开发一种方法，通过这种方法可以识别并最终克服限制多环芳烃降解的因素(S)，这些因素似乎对生物降解具有抵抗力。这些因素可能包括：缺乏大量能够降解这些化合物的微生物；所有生物对化合物的降解率天生很低，其他多环芳烃的存在可能会加剧这种降解率；微生物的生长底物随着时间的推移失去生长底物，从而失去多环芳烃降解活性；微生物的生长底物随着时间的推移失去，从而失去多环芳烃降解活性；不完全代谢的产物积累，可能会抑制一种或多种多环芳烃的降解。致癌多环芳烃的可实现去除可能决定主动生物修复技术在特定地点是否为可接受的技术。此外，在新出现的以风险为基础的场地管理方法下，预计许多场地将保留多环芳烃污染。为了了解这些地点的自然衰减的限度和潜在的长期风险，必须提高我们对多环芳烃降解率和影响这些降解率的因素的了解。这项拟议的研究将量化从各种污染土壤中分离出来的细菌对高分子量多环芳烃的降解率，以及混合物中其他多环芳烃对这些降解率的影响。然后，来自工业现场的实际污染土壤将被处理，将在实验室规模的生物反应器中处理，以研究一种或多种明显顽固的多环芳烃的降解。控制这些化合物降解的因素(S)将通过以下方式阐明：(I)量化处理土壤中能够降解这些化合物的微生物将通过：(I)量化处理土壤中能够降解顽固性多环芳烃的微生物；(Ii)评估添加已知可刺激多环芳烃降解的易降解自然生成化合物的影响；(Iii)检测生物反应器中的液相是否因代谢物积累而抑制多环芳烃降解菌；以及(Iv)检测生物有效性在这些化合物的明显顽固性中的作用。了解了导致目标化合物(S)有限降解的最主要因素(S)后，我们将探索直接在生物反应器中刺激生物降解的方法，并将处理过的土壤从生物反应器中移除。

Polycyclic aromatic hydrocarbons (PAH) are major contaminants in soil and groundwater at a number of sites across the U.S. Many of the PAH are known or suspected carcinogens, yet many are also known to be biodegradable by bacteria and fungi indigenous to native and contaminated soils. Biological processes have been used to remediate PAH-contaminated sites, but removal of the high-molecular weight, carcinogenic species is often incomplete. Since these compounds are poorly soluble in water, their biodegradation of some of the PAH in contaminated systems is limited by factors other than bioavailability. The purpose of this project is to develop approaches by which the factor(s) that limit the degradation of PAH which appear to resist biodegradation can be identified and, eventually, overcome. Such factors can include the absence of significant numbers of microbes able to degrade these compounds; inherently very low rates of degradation of the compound by all organisms, which may be exacerbated by the presence of other PAH; loss of growth substrates for the microorganisms over time and consequent loss of PAH-degrading activity; loss of growth substrates for the microorganisms over time and consequent loss of PAH-degrading activity; and accumulation of products of incomplete metabolism that may inhibit the degradation of one or more PAH. Achievable removals of the carcinogenic PAH may determine whether active bioremediation is an acceptable technology at a given site. In addition, under emerging risk-based approaches to site management such of the PAH contamination is expected to be left in place at many sites. To understand the limits of natural attenuation and potential long-term risks at such sites, it is essential to improve our knowledge of the rates of PAH degradation and the factors that influence these rates. The proposed research will quantify rates of degradation of high-molecular weight PAH by bacteria isolated from a variety of contaminated soils and the effect of other PAH in mixtures on these rates. Then, actual contaminated soils from an industrial site will be treated will be treated in a bench-scale bioreactor to study the degradation of one or more apparently recalcitrant PAH. The factor(s) that govern the degradation of these compounds will be elucidated by: (i) quantifying the organisms in the treated soil that are capable of degrading of these compounds will be elucidated by: (i) quantifying the organisms in the treated soil that are capable of degrading the recalcitrant PAH; (ii) evaluating the effects of adding readily- degraded, naturally occurring compounds known to stimulate PAH degradation; (iii) examining whether the liquid phase in the bioreactor is inhibitory to PAH-degrading bacteria as a result of metabolite accumulation; and (iv) examining the role of bioavailability in the apparent recalcitrance of these compounds. With knowledge of the factor(s) most responsible for limited degradation of the target compound(s), we will then explore methods of stimulating biodegradation either directly in the bioreactor in treated soil removed from the bioreactor.