Substances of unknown or variable composition, complex reaction products, or biological materials (UVCBs) pose unique risk assessment challenges to regulators and to product registrants. These substances can contain many constituents, sometimes partially unknown and/or variable, depending on fluctuations in their source material and/or manufacturing process. International regulatory agencies have highlighted the difficulties in characterizing UVCBs and assessing their toxicity and environmental fate. Several industrial sectors have attempted to address these issues by developing frameworks and characterization methods. Based on the output of a 2016 workshop, this critical review examines current practices for UVCB risk assessment and reveals a need for a multipronged and transparent approach integrating whole-substance and constituent-based information. In silico tools or empirical measurements can provide information on discrete and/or blocks of UVCB constituents with similar hazard properties. Read-across and/or wholesubstance toxicity and fate testing using adapted emerging methods can provide whole-substance information. Continued collaboration of stakeholders representing government, industry, and academia will facilitate the development of practical testing strategies and guidelines for addressing regulatory requirements for UVCBs.
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.
The Challenge:Evolutionary toxicology focuses on the drivers, mechanisms, and outcomes of pollution-driven genetic differentiation among populations. The focal questions address the types of chemical contamination acting as selective pressures; the genetics, epigenetics, and demography of impacted populations; as well as fitness costs and cross-resistances that may follow rapid adaptation. In this field, researchers incorporate tools from environmental chemistry, conservation genetics, population biology, and toxicology to understand the health and stability of impacted populations.Recent studies in evolutionary toxicology have illustrated diverse cases of population-wide adaptation to contamination (killifish, Hyalella, mosquitofish). Adaptation, by definition, is achieved through the localized loss of some individuals and genotypes and, thus, provides singular evidence of losses in biodiversity. Chemical regulations are generally supported by assessments that predict, largely through laboratory studies, the risks associated with chemical exposures. Evolutionary toxicology complements this approach by providing direct evidence of population and community impacts. Recent interest by the Society of Environmental Toxicology and Chemistry working group EVOGENERATE (Evolutionary and Multigenerational Effects of Chemicals) has launched discussions about the utility of evolutionary toxicology studies to inform chemical regulation. To further this discussion, one representative from each of 3 sectors, academia, government, and industry, was asked to provide opinions on the following questions:1) The considerable number of adaptive events reported in recent years suggests that current risk-assessment methods may not be exhaustive. What is risk assessment missing by not incorporating evolutionary toxicology endpoints to inform the regulation of toxic compounds? 2) Changes in the US Toxic Substances Control Act call for attention in 2 major aspects of predictive toxicology: organizational frameworks (e.g., adverse outcomes pathway) and fast screening methods (e.g., Omics, Tox21). Can evolutionary toxicology contribute to these advancements? 3) What needs to be done to make an evolutionary approach more accessible and useful to chemical regulation?
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