Modernizing persistence–bioaccumulation–toxicity (PBT) assessment with high throughput animal-free methods

Abstract

The assessment of persistence (P), bioaccumulation (B), and toxicity (T) of a chemical is a crucial first step at ensuring chemical safety and is a cornerstone of the European Union’s chemicals regulation REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals). Existing methods for PBT assessment are overly complex and cumbersome, have produced incorrect conclusions, and rely heavily on animal-intensive testing. We explore how new-approach methodologies (NAMs) can overcome the limitations of current PBT assessment. We propose two innovative hazard indicators, termed cumulative toxicity equivalents (CTE) and persistent toxicity equivalents (PTE). Together they are intended to replace existing PBT indicators and can also accommodate the emerging concept of PMT (where M stands for mobility). The proposed “toxicity equivalents” can be measured with high throughput in vitro bioassays. CTE refers to the toxic effects measured directly in any given sample, including single chemicals, substitution products, or mixtures. PTE is the equivalent measure of cumulative toxicity equivalents measured after simulated environmental degradation of the sample. With an appropriate panel of animal-free or alternative in vitro bioassays, CTE and PTE comprise key environmental and human health hazard indicators. CTE and PTE do not require analytical identification of transformation products and mixture components but instead prompt two key questions: is the chemical or mixture toxic, and is this toxicity persistent or can it be attenuated by environmental degradation? Taken together, the proposed hazard indicators CTE and PTE have the potential to integrate P, B/M and T assessment into one high-throughput experimental workflow that sidesteps the need for analytical measurements and will support the Chemicals Strategy for Sustainability of the European Union.

Sustainable synthesis: natural processes shaping the nanocircular economy

“…Bioaccumulation, on the other hand, refers to the tendency of certain substances to build up in the tissues of living organisms over time. 132 Recommendations take into account the potential for bioaccumulation, particularly in aquatic organisms, and establish limits to prevent adverse effects. Notably, ecotoxicity strategies consider the potential for long-term environmental damage caused by the use or release of certain materials which includes the assessment of their potential for contamination of soil, water bodies, or air.…”

Should Transformation Products Change the Way We Manage Chemicals?

“…This high degree of parallelization allowed for highthroughput persistence testing but rendered it nearly impossible to assess mineralization and link detected TPs to their precursors within one experiment. Escher et al 74 proposed an experimental coupling of biotransformation experiments and high-throughput in vitro bioassays for P and t testing, which forgoes chemical analysis in favor of a "persistent toxicity" assessment. The advantage of this method is that it essentially treats parent compounds and TPs equally, since both persistent and toxic parent compounds or toxic TPs may cause this "persistent toxicity".…”

“…Escher et al. 74 proposed an experimental coupling of biotransformation experiments and high-throughput in vitro bioassays for P and t testing, which forgoes chemical analysis in favor of a “persistent toxicity” assessment. The advantage of this method is that it essentially treats parent compounds and TPs equally, since both persistent and toxic parent compounds or toxic TPs may cause this “persistent toxicity”.…”

New approach methods to assess developmental and adult neurotoxicity for regulatory use: a PARC work package 5 project

“…Currently, in vitro data may be used in Weight of Evidence assessment for classification and labelling (e.g., for developmental toxicity), or to trigger further DNT tests at REACH Annex IX and X, or to support grouping and read across from similar substances. High-throughput in vitro assays have also great potential as screening tools to prioritize chemicals and specific modes of action (MoA) for further testing ( Escher et al, 2023 ). While such high throughput screening (HTS) tools have not yet been implemented for DNT and ANT in large scale regulatory practice, the introduction of more sophisticated in vitro tests and the validation of all HTS assays for DNT and ANT appear vital to improve their regulatory usefulness.…”