Microbial Transformation of Organic Chemicals in Soil Through Cometabolism and Bioavailability Assessment of the Parent Chemical and Transformation Products

Abstract

Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.The main objective in this study was to integrate the bioavailability assessment in an approach that followed the OECD 307 mineralization and biodegradation guideline, where polar metabolites of a model non-ionic compound (pyrene) were produced by cometabolism. The integration of bioavailability assessments in contaminated soils is necessary for risks assessments and remediation approaches. In these measurements, the persistence of organic compounds in the soils plays a very important role. The incomplete biodegradation of these compounds through cometabolism, leading to transformation products, could even increase the risks, that is also important. Therefore, integrating cometabolic transformations in bioavailability determinations will lead to more realistic risk assessment of the bioremediation processes. A standardized method (ISO 16751:2020), based on Tenax extraction at 20 hours was used to measure bioavailability. This is a chemical method, preferably used with hydrophobic chemicals (Kow > 3), in which the potential bioavailable fraction is the amount of contaminant present in the matrix that can be released from the solid phase to the aqueous phase in a well-mixed water soil mixture and in presence of a receiving phase (Tenax). For this reason, the physico-chemical properties of the compounds in the system, is a very important factor that can affect the results of bioavailability and it is the objective of this study. The first step was an experiment in which the microbial transformation of 14C-pyrene by cometabolism assured the presence of transformation products in the system. In this way, the soil bacterium Pseudomonas putida G7 was used, and a passive dosing device (silicone O-rings) in a soil slurry experiment to control the release of the parent compound to the aqueous phase. The results of this experiment indicated that water soluble metabolites were produced and some possible metabolites were analyzed too (Fernández-López, et al., 2020). Then, we performed a bioavailability assessment to evaluate the effectiveness of this Tenax-based ISO method, and possible ways of optimization, in presence of the metabolites of pyrene, which are more hydrophilic compounds and therefore tended to remain in the aqueous phase and to sorb back to the soil. The results could be applied in future experiments with other compounds, such as pharmaceuticals, which are usually transformed partially as a result of their biological processing in soil.N