Hydrochemical Conditions for Aerobic/Anaerobic Biodegradation of Chlorinated Ethenes—A Multi-Site Assessment

• Main Authors: Jan Němeček, Kristýna Marková, Roman Špánek, Vojtěch Antoš, Petr Kozubek, Ondřej Lhotský, Miroslav Černík
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: Water
• Subjects: chlorinated solvents; biological reductive dechlorination; aerobic oxidation; qpcr; ethenotrophs; methanotrophs
• Online Access: https://www.mdpi.com/2073-4441/12/2/322

A stall of <i>cis</i>-1,2-DCE and vinyl chloride (VC) is frequently observed during bioremediation of groundwater chloroethenes via reductive dechlorination. These chloroethenes may be oxidised by aerobic methanotrophs or ethenotrophs co-metabolically and/or metabolically. We assessed the potential for such oxidation at 12 sites (49 groundwater samples) using hydrochemical and molecular biological tools. Both ethenotroph (<i>etnC</i> and <i>etnE</i>) and methanotroph (<i>mmoX</i> and <i>pmoA</i>) functional genes were identified in 90% of samples, while reductive dehalogenase functional genes (<i>vcrA</i> and <i>bvcA</i>) were identified in 82%. All functional genes were simultaneously detected in 78% of samples, in actively biostimulated sites in 88% of samples. Correlation analysis revealed that <i>cis</i>-1,2-DCE concentration was positively correlated with <i>vcrA</i>, <i>etnC</i> and <i>etnE</i>, while VC concentration was correlated with <i>etnC</i>, <i>etnE</i>, <i>vcrA</i> and <i>bvcA</i>. However, feature selection based on random forest classification indicated a significant relationship for the <i>vcrA</i> in relation to <i>cis</i>-1,2-DCE, and <i>vcrA</i>, <i>bvcA</i> and <i>etnE</i> for VC and no prove of relationship between <i>cis</i>-1,2-DCE or VC and the methanotroph functional genes. Analysis of hydrochemical parameters indicated that aerobic oxidation of chloroethenes by ethenotrophs may take place under a range of redox conditions of aquifers and coincide with high ethene and VC concentrations.