Moving persistence assessments into the 21st century: A role for weight‐of‐evidence and overall persistence

Abstract

Assessing the persistence of chemicals in the environment is a key element in existing regulatory frameworks to protect human health and ecosystems. Persistence in the environment depends on many fate processes, including abiotic and biotic transformations and physical partitioning, which depend on substances' physicochemical properties and environmental conditions. A main challenge in persistence assessment is that existing frameworks rely on simplistic and reductionist evaluation schemes that may lead substances to be falsely assessed as persistent or the other way around—to be falsely assessed as nonpersistent. Those evaluation schemes typically assess persistence against degradation half‐lives determined in single‐compartment simulation tests or against degradation levels measured in stringent screening tests. Most of the available test methods, however, do not apply to all types of substances, especially substances that are poorly soluble, complex in composition, highly sorptive, or volatile. In addition, the currently applied half‐life criteria are derived mainly from a few legacy persistent organic pollutants, which do not represent the large diversity of substances entering the environment. Persistence assessment would undoubtedly benefit from the development of more flexible and holistic evaluation schemes including new concepts and methods. A weight‐of‐evidence (WoE) approach incorporating multiple influencing factors is needed to account for chemical fate and transformation in the whole environment so as to assess overall persistence. The present paper's aim is to begin to develop an integrated assessment framework that combines multimedia approaches to organize and interpret data using a clear WoE approach to allow for a more consistent, transparent, and thorough assessment of persistence. Integr Environ Assess Manag 2022;18:868–887. © 2021 ExxonMobil Biomedical Sciences, Inc. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Machine Learning-Based Models with High Accuracy and Broad Applicability Domains for Screening PMT/vPvM Substances

“…Our system was constructed with conventional, ensemble, and deep learning algorithms on the basis of a large dataset, showing excellent interpretability, broad ADs, good generalization capability, and high accuracy, especially in the prediction of false-negative substances. We expected that the screening system is not only limited to the current algorithms and database but it also can better serve with the adoption of the integrated assessment framework of persistence, 52 uniform toxicity data that can be retrieved from various exposure scenarios, and more chemicals with more enriched data, including ionic organic compounds, properties with balanced numbers of substances, 3D chemical structure images using Graph Neural Networks, as well as realtime modeling features for updating chemical information. Our research contributes to the management of PMT/vPvM substances over the complete life cycle, particularly in China, with its size of chemical industry larger than the EU and U.S. combined.…”

Assessing the Persistence and Mobility of Organic Substances to Protect Freshwater Resources

“…Not allowing for weight-of-evidence conclusions would expand the number of "Potential P/vP" and "insufficient data" conclusions while decreasing the number of "Not P" and P/vP conclusions. If one were to introduce an alternative persistency threshold instead of media specific half-lives, like the emission scenario dependent multimedia parameter P ov , 155 this would either severely restrict the number of substances considered P/vP if intense data requirements are needed, or would have an unknown impact if low data quality modeling threshold values are introduced as weight-of-evidence. If the readily/inherent biodegradability tests were used as the threshold for P, the Potential PMT/vPvM substances would become PM, PMT, or vPvM.…”

Scientific concepts and methods for moving persistence assessments into the 21st century

“…McLachlan and colleagues further extended this idea, suggesting that all laboratory tests could include a reference benchmark chemical substance against which the relative biodegradation (extent or rate) of test chemical substances could be measured (McLachlan et al, 2017), a concept that they termed benchmarking (Table 3). They further demonstrated how the concept could be used to separate degradation half‐lives from dissipation processes in the field (a lake system; see Redman et al, 2021) and outlined its use more generally in chemical hazard and risk assessments, in particular, in calibrating and translating laboratory to field data. More recently, the same group demonstrated that comparable half‐life determinations between field‐derived and OECD TG 309 simulation tests were obtained if the tests were not spiked with a given test substance, but where biodegradation of substances in the natural waters was followed by targeted (Li & McLachlan, 2019) or nontargeted chemical analyses (Li & McLachlan, 2020).…”