Once released into the environment, petroleum is exposed to biological and physical weathering processes which can lead to the formation and accumulation of highly recalcitrant polar compounds. These polar compounds are often challenging to analyse and can be present as an “unresolved complex mixture” (UCM) in total petroleum hydrocarbon (TPH) analyses and can be mistaken for natural organic matter. Existing research on UCMs comprised of polar compounds is limited, with a majority of the compounds remaining unidentified and their long-term persistence unknown. Here, we investigated the potential biodegradation of these recalcitrant polar compounds isolated from weathered diesel contaminant, and the changes in the microbial community composition associated with the biodegradation process. Microcosms were used to study the biodegradability of the polar compounds under various aerobic and anaerobic conditions and the results compared against the biodegradation of fresh diesel. Under all conditions tested, the majority of the polar UCM contaminant remained recalcitrant to biodegradation. The degradation was limited to the TPH portion of the polar UCM, which represented a minor fraction of the total polar UCM concentration. Changes in microbial community composition were observed under different redox conditions and in the presence of different contaminants. This work furthers the understanding of the biodegradation and long-term recalcitrance of polar compounds formed through weathering at contaminated legacy sites.

中文翻译：

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由风化柴油形成的极性化合物的生物降解性。

石油一旦释放到环境中，便会暴露于生物和物理风化过程中，这可能导致高难降解极性化合物的形成和积累。这些极性化合物通常难以分析，在总石油烃（TPH）分析中可能以“未解析的复杂混合物”（UCM）的形式存在，并且可能被误认为是天然有机物。现有的关于由极性化合物组成的UCM的研究是有限的，大多数化合物尚未确定，其长期持久性未知。在这里，我们调查了从风化的柴油污染物中分离出来的这些顽固极性化合物的潜在生物降解，以及与生物降解过程相关的微生物群落组成的变化。微观世界被用来研究极性化合物在各种好氧和厌氧条件下的生物降解能力，并将结果与​​新鲜柴油的生物降解进行了比较。在所有测试条件下，大多数极性UCM污染物仍然难以降解。降解仅限于极性UCM的TPH部分，占总极性UCM浓度的一小部分。在不同的氧化还原条件下和存在不同污染物的情况下，观察到微生物群落组成的变化。这项工作使人们进一步了解了受污染的遗留场所因风化而形成的极性化合物的生物降解和长期不耐受性。