Examination of the endocrine-disrupting properties of “active chlorine generated from seawater by electrolysis” in response to the European Biocidal Products Regulation: current knowledge and methodological challenges

Background

Currently, active chlorine is considered the most effective treatment for preventing biofouling of structures in contact with seawater. This compound falls under the scope of the EU Biocidal Products Regulation, which includes since 2018 a requirement to assess all active ingredients for their potential endocrine-disrupting properties on humans and non-target organisms. Therefore, this study examines the endocrine-disrupting (ED) potential of active chlorine based on the European Chemicals Agency and European Food Safety Authority guidance (ED TGD). It includes two approaches: (i) a systematic literature review using appropriate search terms and (ii) an in silico assessment, both supported by expert judgement. Finally, the feasibility and relevance of in vitro tests were examined by considering the stability of chlorine and the applicability domain of the recommended in vitro assays.

Results

No significant adversity or endocrine activity based on EATS (estrogen, androgen, thyroid, and steroidogenesis)-modalities were evidenced based on the literature data. However, these modalities remain understudied and further datasets are needed for a comprehensive assessment. The in silico approach revealed a low probability of binding between active chlorine and a set of 14 human nuclear receptors, for both agonist and antagonist effects. This is not surprising given the great structural difference between active chlorine and natural ligands. The in vitro investigation of the ED potential of active chlorine raises several operational limits, including: (i) its instability (t_1/2 < 48 h) which is incompatible with a reasonable time window between collection and ex situ analysis; (ii) its rapid and complete reaction with several essential nutrients in cell culture media; (iii) its documented cytotoxicity on various cell lines; and (iv) its exclusion from the scope of certain OECD guidelines.

Conclusions

Overall, neither the in silico evaluation nor the systematic literature review performed indicates a significant adversity based on EATS-mediated parameters or EATS-related endocrine activities. This study highlights the challenges of performing a comprehensive ED assessment for a data-poor chemical and questions the relevance of transposing generic methodologies to the case of unstable and inorganic molecules.