Cyclohexane and some of its derivatives have been a major concern because of their significant adverse human health effects and widespread occurrence in the environment. The 2014 West Virginia chemical spill has raised public attention to (4-methylcyclohexyl)methanol (4-MCHM), one cyclohexane derivative, which is widely used in coal processing but largely ignored. In particular, the environmental fate of its primary components, cis- and trans-4-MCHM, remains largely unexplored. This study aimed to investigate the degradation kinetics and mineralization of cis- and trans-4-MCHM by sediment microorganisms under aerobic and anaerobic conditions. We found the removal of cis- and trans-4-MCHM was mainly attributed to biodegradation with little contribution from sorption. A nearly complete aerobic degradation of 4-MCHM occurred within 14days, whereas the anaerobic degradation was reluctant with residual percentages of 62.6% of cis-4-MCHM and 85.0% of trans-4-MCHM after 16-day incubation. The cis-4-MCHM was degraded faster than the trans under both aerobic and anaerobic conditions, indicating an isomer-specific degradation could occur during the 4-MCHM degradation. Nitrate addition enhanced 4-MCHM mineralization by about 50% under both aerobic and anaerobic conditions. Both cis- and trans-4-MCHM fit well with the first-order kinetic model with respective degradation rates of 0.46-0.52 and 0.19-0.31day-1 under aerobic condition. Respective degradation rates of 0.041-0.095 and 0.013-0.052day-1 occurred under anaerobic condition. One bacterial strain capable of effectively degrading 4-MCHM isomers was isolated from river sediments and identified as Bacillus pumilus at the species level based on 16S rRNA gene sequence and 97% identity. Our findings will provide critical information for improving the prediction of the environmental fate of 4-MCHM and other cyclohexane derivatives with similar structure as well as enhancing the development of feasible treatment technologies to mitigate these compounds.
Bibliographical noteThis work was supported by Dr. Zhang's startup funds provided by Virginia Tech College of Engineering. L. Y. gratefully acknowledges support from China Scholarship Council. This research was performed in conjunction with 4-MCHM research projects supported by the National Science Foundation , CBET Award # 1424234 . We thank Dr. Hualan Liu, David Collins, and Kaisen Lin for their help with the isolation and identification of 4-MCHM-degrading bacteria. We also thank Amanda Sain for assistance with analytical methods and GC-headspace measurements.
- 4-MCHM isomers
- 4-MCHM-degrading bacteria
- Crude (4-methylcyclohexyl)methanol
- Degradation kinetics
- West Virginia chemical spill