期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 55, 期 11, 页码 7386-7397出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.0c08566
关键词
bioavailability; 2,6-dichlorobenzamide; reactive-transport model; flow-through system; GC-IRMS; CSIA
资金
- ERC [616861]
- European Research Council (ERC) [616861] Funding Source: European Research Council (ERC)
Research shows that isotope fractionation decreases significantly when organic pollutant concentrations fall below a certain level, indicating that membrane transfer is slow relative to enzyme turnover. By using a reactive transport model, it is possible to identify mass transfer limitations in biodegradation, especially at low concentrations.
Organic contaminant degradation by suspended bacteria in chemostats has shown that isotope fractionation decreases dramatically when pollutant concentrations fall below the (half-saturation) Monod constant. This masked isotope fractionation implies that membrane transfer is slow relative to the enzyme turnover at mu g L-1 substrate levels. Analogous evidence of mass transfer as a bottleneck for biodegradation in aquifer settings, where microbes are attached to the sediment, is lacking. A quasi-two-dimensional flow-through sediment microcosm/tank system enabled us to study the aerobic degradation of 2,6-dichlorobenzamide (BAM), while collecting sufficient samples at the outlet for compound-specific isotope analysis. By feeding an anoxic BAM solution through the center inlet port and dissolved oxygen (DO) above and below, strong transverse concentration cross-gradients of BAM and DO yielded zones of low (mu g L-1) steady-state concentrations. We were able to simulate the profiles of concentrations and isotope ratios of the contaminant plume using a reactive transport model that accounted for a mass-transfer limitation into bacterial cells, where apparent isotope enrichment factors *e decreased strongly below concentrations around 600 mu g/L BAM. For the biodegradation of organic micropollutants, mass transfer into the cell emerges as a bottleneck, specifically at low (mu g L-1) concentrations. Neglecting this effect when interpreting isotope ratios at field sites may lead to a significant underestimation of biodegradation.
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