The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes. In this paper, we address the challenges and limitations facing current test methods and the scientific advances that are helping to both understand and provide solutions to them. Some of these advancements include the following: (1) robust methods that provide a deeper understanding of microbial composition, diversity, and abundance to ensure consistency and/or interpret variability between tests; (2) benchmarking tools and reference substances that aid in persistence evaluations through comparison against substances with well-quantified degradation profiles; (3) analytical methods that allow quantification for parent and metabolites at environmentally relevant concentrations, and inform on test substance bioavailability, biochemical pathways, rates of primary versus overall degradation, and rates of metabolite formation and decay; (4) modeling tools that predict the likelihood of microbial biotransformation, as well as biochemical pathways; and (5) modeling approaches that allow for derivation of more generally applicable biotransformation rate constants, by accounting for physical and/or chemical processes and test system design when evaluating test data. We also identify that, while such advancements could improve the certainty and accuracy of persistence assessments, the mechanisms and processes by which they are translated into regulatory practice and development of new OECD test guidelines need improving and accelerating. Where uncertainty remains, holistic weight of evidence approaches may be required to accurately assess the persistence of chemicals. Integr Environ Assess Manag 2022;1-34.
Current biodegradation screening
tests are not specifically designed
for persistence assessment of chemicals, often show high inter- and
intra-test variability, and often give false negative biodegradation
results. Based on previous studies and recommendations, an international
ring test involving 13 laboratories validated a new test method for
marine biodegradation with a focus on improving the reliability of
screening to determine the environmental degradation potential of
chemicals. The new method incorporated increased bacterial cell concentrations
to better represent the microbial diversity; a chemical is likely
to be exposed in the sampled environments and ran beyond 60 days,
which is the half-life threshold for chemical persistence in the marine
environment. The new test provided a more reliable and less variable
characterization of the biodegradation behavior of five reference
chemicals (sodium benzoate, triethanolamine, 4-nitrophenol, anionic
polyacrylamide, and pentachlorophenol), with respect to REACH and
OSPAR persistence thresholds, than the current OECD 306 test. The
proposed new method provides a cost-effective screening test for non-persistence
that could streamline chemical regulation and reduce the cost and
animal welfare implications of further higher tier testing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.