Release of benzene, toluene, ethylbenzene, and xylene (BTEX) as components of the light non-aqueous phase liquids (LNAPL) contaminates soil and groundwater. Assessing the mechanisms of degradation and mineralization of BTEX in groundwater helps understand the migration of the dissolved plume, enabling the reduction of risks to humans. Here, we studied the fate of ethylbezene, m,p-xylenes and o-xylenes and the accompanying formation of methane in a Cenozoic lateritic aquifer in Brazil by compound-specific carbon stable isotope analysis (CSIA), to gain insights into the complex dynamics of release and biodegradation of BTEX in the LNAPL source zone. The enrichment of ∂¹³C in aromatic compounds dissolved in groundwater compared to the corresponding compounds in LNAPL indicate that CSIA can provide valuable information regarding biodegradation. The isotopic analysis of methane provides direct indication of oxidation mediated by aquifer oxygenation. The ∂¹³C-CO₂ values indicate methanogenesis prevailing at the border and aerobic biodegradation in the center of the LNAPL source zone. Importantly, the isotopic results allowed major improvements in the previously developed conceptual model, supporting the existence of oxic and anoxic environments within the LNAPL source zone.

轻质非水相液体（LNAPL）的成分苯，甲苯，乙苯和二甲苯（BTEX）的释放污染了土壤和地下水。评估地下水中BTEX的降解和矿化机制有助于了解溶解羽流的迁移，从而降低对人类的危害。在这里，我们通过化合物特异性碳稳定同位素分析（CSIA）研究了巴西新生代红土含水层中乙基苯，间二甲苯，对二甲苯和邻二甲苯的命运以及甲烷的伴随形成，以了解复杂的动力学LNAPL源区中BTEX的释放和生物降解过程。富集∂ ¹³与LNAPL中的相应化合物相比，溶于地下水的芳族化合物中的C表示CSIA可提供有关生物降解的有价值的信息。甲烷的同位素分析可直接指示由含水层充氧引起的氧化。所述∂ ¹³ C-CO ₂值表明甲烷在LNAPL源区域的中心处的边界和好氧生物降解盛行。重要的是，同位素结果允许对先前开发的概念模型进行重大改进，从而支持LNAPL源区内存在有氧和无氧环境。