Comparison of Small Molecule Biotransformation Half-Lives between Activated Sludge and Soil: Opportunities for Read-Across?

Abstract

Compartment-specific degradation half-lives are essential pieces of information in the regulatory risk assessment of synthetic chemicals. However, their measurement according to regulatory testing guidelines is laborious and costly. Despite the obvious ecological and economic benefits of knowing environmental degradability as early as possible, its consideration in the early phases of rational chemical design is therefore challenging. Here, we explore the possibility to use half-lives determined in highly time-and work-efficient biotransformation experiments with activated sludge and mixtures of chemicals to predict soil half-lives from regulatory simulation studies. We experimentally determined half-lives for 52 structurally diverse agrochemical active ingredients in batch reactors with three concentrations of the same activated sludge. We then developed bi-and multivariate models for predicting half-lives in soil by regressing the experimentally determined half-lives in activated sludge against average soil half-lives of the same chemicals extracted from regulatory data. The models differed in how we accounted for sorption-related bioavailability differences in soil and activated sludge. The best performing models exhibited good coefficients-of-determination (R 2 of around 0.8), low average errors (< factor of 3 in half-life predictions) and were robust in cross-validation. From a practical perspective, these results suggest that it may indeed be possible to read across from half-lives determined in highly efficient biotransformation experiments in activated sludge to soil half-lives, which are obtained from much more work-and resource-intense regulatory studies, and that these predictions are clearly superior to predictions based on the output of the publicly available BIOWIN QSBR model. From a theoretical perspective, these results suggest that soil and activated sludge microbial communities, although certainly different in terms of taxonomic composition, may be functionally similar with respect to the enzymatic transformation of environmentally relevant concentrations of a diverse range of chemical compounds.

Impact of long-term irrigation with municipal reclaimed wastewater on the uptake and degradation of organic contaminants in lettuce and leek

“…Valsartan biodegradation in activated sludge was reported to be very fast (< 0.5 d, Helbling et al, 2010). Even though this value was reported in activated sludge experiments, similar behavior may be expected in soil irrigated with organic rich WW because it seems to be possible to read across from half-lives determined in highly efficient biotransformation experiments such as activated sludge to soil half-lives due to similarity in enzymatic transformations of organic contaminants (Fenner et al, 2020).…”

Understanding the Dependence of Micropollutant Biotransformation Rates on Short-Term Temperature Shifts

“…It is well known that microbial communities of WWTP and other biological systems vary spatially. Therefore it is uncertain how our current results would have differed if we sampled at another location or time, though mechanisms of microbial transformation and associated rate constants for selected chemicals have been shown to be similar across different environmental compartments 25,69 .…”

“…Activated sludge was chosen as a model system for the experimental studies, due to its intrinsic microbial complexity and the facility to manipulate and maintain homogeneous process conditions in laboratory studies. Furthermore, biotransformation laboratory assays with activated sludge can provide valuable information on the kinetics of mixtures of chemicals not only for full-scale WWTPs, but also for alternative biological systems, such as soil 25 . A series of laboratory-based assays were carried out to closely monitor both micropollutant biotransformation, and compositional and activity changes in the microbial community under short-term temperature manipulations, over a 4-40°C range.…”

Chemical Innovation for Sustainable Agriculture by Investing in Soil Health

“…Therefore, new alternative predictive approaches able to provide swiftly and in a high-throughput manner indications about degradation are highly valuable. [28,29] A few recent investigations harvested some encouraging results, the published approach hinged on the fast evaluation of the degradation kinetics of a wide range of compounds on activated sludge systems and used this to predict soil half-lives from studies with a regulatory setting. Satisfactory predictions across a wide range of agrochemicals were observed and were superior to other approaches relying on other available predictive models.…”