Quantification of the microbial and chemical-oxidative degradation of NSO-heterocycles

Groundwater sampling to investigate NSO-HET microbiological degradation at a tar oil contaminated site

The NSO-HET substance group includes creosote-like pollutants and is classified similarly to PAHs as hazardous to groundwater. The aim of this research project was to develop methods to quantify microbial and chemical oxidative degradation of NSO heterocycles using flow cytometry and isotope fractionation (IF).

The quantifying of the degradation of creosote-like NSO-heterocycles (NSO-HET) is important for the assessment of natural and enhanced natural attenuation (NA/ENA) as well as for the use of in-situ chemical oxidation processes (ISCO).

In ISCO remediation, the oxidation of NSO-HET is basically promising. This has been demonstrated in the laboratory for binuclear substances (isoquinoline, benzothiophene, benzofuran) using the oxidants peroxodisulfate and Fenton's reagent, respectively. With higher-nucleation NSO-HET or with weaker oxidants, the degradation rates decreased significantly. The limitations of the ISCO method lie particularly in the incomplete oxidation of the contaminants. However, with subsequent microbial stimulation, slower oxidizable HET as well as transformation products continued to degrade microbially at a rapid rate.

With flow cytometry, a robust biomonitoring method could be developed that is very well suited for the rapid assessment of bioactivity at contaminated sites. It is suitable for orienting initial assessments of microbial degradation potential and as a complementary tool for plausibility testing in NA investigations (fig.).

The isotopic measurements showed abiotic as well as biotic 13C/12C IF during chemical oxidation and aerobic microbial degradation, respectively. In particular, the suitability of 13C/12C isotopic measurements for the evaluation of aerobic processes for binuclear NSO-HET was demonstrated.


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Salowsky, H.; Schäfer, W.; Schneider, A.-L.; Müller, A.; Dreher, C.; Tiehm, A.: Beneficial effects of dynamic groundwater flow and redox conditions on Natural Attenuation of mono-, poly-, and NSO-heterocyclic hydrocarbons. Journal of Contaminant Hydrology 243: 103883 (2021) DOI: 10.1016/j.jconhyd.2021.103883