Biodegradation of high molecular weight PAHs in contaminated soil

多环芳烃（PAH）是美国许多地区土壤和地下水中的主要污染物。许多多环芳烃是已知或疑似致癌物，但也有许多已知可被原生土壤和污染土壤中的细菌和真菌生物降解。生物过程已被用于修复多环芳烃污染的场所，但去除高分子量的致癌物质往往是不完整的。由于这些化合物难溶于水，它们在污染系统中对一些多环芳烃的生物降解受到生物利用度以外因素的限制。这个项目的目的是发展各种方法，通过这些方法，可以确定并最终克服限制多环芳烃降解的因素，而多环芳烃似乎无法进行生物降解。这些因素可以包括缺乏大量能够降解这些化合物的微生物；所有生物对该化合物的固有降解率非常低，而其他多环芳烃的存在可能会加剧这种降解率；随着时间的推移，微生物失去了生长基质，从而失去了降解多环芳烃的活性；随着时间的推移，微生物失去了生长基质，从而失去了降解多环芳烃的活性；不完全代谢产物的积累可能抑制一种或多种多环芳烃的降解。可实现的致癌多环芳烃的去除可以决定活性生物修复在给定部位是否是一种可接受的技术。此外，在新兴的基于风险的场地管理方法下，预计多环芳烃污染将留在许多场地。为了了解这些地点自然衰减的极限和潜在的长期风险，有必要提高我们对多环芳烃降解速率和影响这些速率的因素的认识。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速率以及混合物中其他多环芳烃对这些速率的影响。然后，实际污染的土壤从一个工业场地将被处理将在一个实验规模的生物反应器中处理，以研究一种或多种明显顽固性多环芳烃的降解。控制这些化合物降解的因素将通过：(i)量化处理土壤中能够降解这些化合物的生物将通过：(i)量化处理土壤中能够降解顽固性多环芳烃的生物来阐明；（ii）评估添加容易降解的、已知会刺激多环芳烃降解的天然化合物的影响；（iii）检查生物反应器内的液相是否因代谢物积聚而对多环芳烃降解细菌有抑制作用；（iv）检查生物利用度在这些化合物的明显顽固性中的作用。随着对目标化合物有限降解的主要原因的了解，我们将探索直接在生物反应器中刺激生物降解的方法，或者在从生物反应器中取出的处理过的土壤中。

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.