Prediction of the Formation of Biogenic Nonextractable Residues during Degradation of Environmental Chemicals from Biomass Yields

Abstract

Degradation tests with radio or stable isotope labeled compounds enable the detection of the formation of nonextractable residues (NER). In PBT and vPvB assessment, remobilisable NER are considered as a potential risk while biogenic NER from incorporation of labeled carbon into microbial biomass are treated as degradation products. Relationships between yield, released CO (as indicator of microbial activity and mineralization) and microbial growth can be used to estimate the formation of biogenic NER. We provide a new approach for calculation of potential substrate transformation to microbial biomass (theoretical yield) based on Gibbs free energy and microbially available electrons. We compare estimated theoretical yields of biotechnological substrates and of chemicals of environmental concern with experimentally determined yields for validation of the presented approach. A five-compartment dynamic model is applied to simulate experiments of C-labeled 2,4-D and ibuprofen turnover. The results show that bioNER increases with time, and that most bioNER originates from microbial proteins. Simulations with precalculated input data demonstrate that precalculation of yields reduces the number of fit parameters considerably, increases confidence in fitted kinetic data, and reduces the uncertainty of the simulation results.

Microbial Controls on the Biogeochemical Dynamics in the Subsurface

“…As shown by VanBriesen (2002) and for a variety of organic carbon compounds and metabolic pathways (aerobic degradation, denitrification and methanogenesis), energy dissipation approaches are consistent with empirically based methods and predict quite similar yields with laboratory-determined values of Y. A slightly less complex theoretical approach has also recently been developed (the so-called Microbial Turnover to Biomass (MTB) method of Trapp et al (2018)) and applied to the quantification of pesticide degradation and formation of biogenic non-extractable residues (Brock et al 2017). Overall, the major drawback of these theoretical calculations is that they provide only maximum Y values, and do not consider energy changes due to variations in chemical composition of the system (Thullner et al 2007).…”

Certainties and uncertainties in accessing toxicity of non-extractable residues (NER) in soil

“…Only 1.9, 2.9 and 4%, respectively, of added cypermethrin was mineralized. In line with this low mineralization, incorporation of radiolabelled 14 C in biomass should be low [29] and NER in this experiment is considered more likely to be entrapped parent compound or a breakdown product.…”

“…If type III NER are present in the matrix, they will stay either in the solid matrix after silylation and as such contribute to the type II NER or they become dissolved and add to type I NER. Therefore, computer models have been developed, to estimate biogenic NER based on the measured mineralization of the chemical (MTB method, [29]). Apart from the approach according to Kästner et al [22], other concepts were developed (e.g.…”

Can a chemical be both readily biodegradable AND very persistent (vP)? Weight-of-evidence determination demonstrates that phenanthrene is not persistent in the environment

“…Type I NER). Chemicals that are rapidly mineralised are prone to the formation of biomass (Type III NER) [153,161]. Phenanthrene, as a chemical that undergoes rapid mineralisation, is therefore likely to form appreciable amounts of Type III NER.…”