ECHA ARN documents: chemical grouping without a toxicological rationale

Grouping of esters of 4-hydroxybenzoic acid for hazard assessment

Hazardous properties of a large number of esters of 4-hydroxybenzoic acid (parabens) have been proposed by ECHA to be assessed as a group. We recommend to restrict the grouping approach to short chain esters, i.e. methyl, ethyl, propyl and butyl paraben which are very similar in chemical structures, physicochemical properties, toxicokinetics, and hazardous properties. While these parabens show a weak estrogenicity in some in vitro or in vivo screening assays, they do not induce estrogen-receptor-mediated adverse effects in intact animals. Therefore, there is no support regarding classification and labeling of endocrine disruption or reproductive toxicity of these parabens.

Grouping approaches based on structure alone are insufficient to conclude about toxicological properties-the example of monoamine-based chelates

Aminocarboxylic acid (monoamine-based) chelating agents such as GLDA, MGDA, NTA, and EDG are widely used in a variety of products and processes. In the European Union, based on the Green Deal and the Chemicals Strategy for Sustainability (CSS), there is an increasing tendency to speed up chemical hazard evaluation and to regulate chemicals by grouping substances based on molecular structure similarity. Recently, it was proposed to group polycarboxylic acid monoamines, hydroxy derivatives and their salts with monovalent cations, and to consider all group members as potential carcinogens based on the official CLP classification of one group member, viz. NTA, which is classified as suspected carcinogen Cat. 2. In this review, we show that a grouping approach for harmonized classification and labeling based on molecular structure alone, disregarding existing animal test data as well as current scientific and regulatory knowledge, would result in incorrect classification. Using such a simplistic, although considered pragmatic approach, classification of all group members upfront would not improve protection of human health. Instead, it could not only lead to unnecessary additional vertebrate animal testing but also to onerous and disproportionate restrictions being placed on the use of these valuable substances; some of these even being considered as green chemicals.

Refine and Strengthen SAR-Based Read-Across by Considering Bioactivation and Modes of Action

Structure-activity relationship (SAR)-based read-across is an important and effective method to establish the safety of a data-poor target chemical (structure of interest (SOI)) using hazard data from structurally similar source chemicals (analogues). Many methods use quantitative similarity scores to evaluate the structural similarity for searching and selecting analogues as well as for evaluating analogue suitability. However, studies suggest that read-across based purely on structural similarity cannot accurately predict the toxicity of an SOI. As mechanistic data become available, we gain a greater understanding of the mode of action (MOA), the relationship between structures and metabolism/bioactivation pathways, and the existence of "activity cliffs" in chemical chain length, which can improve the analogue rating process. For this purpose, the current work identifies a series of classes of chemicals where a small change at a key position can result in a significant change in metabolism and bioactivation pathways and may eventually result in significant changes in chemical toxicity that have a big impact on the suitability of analogues for read-across. Additionally, a series of SAR-based read-across case studies are presented, which cover a variety of chemical classes that commonly link to different toxic endpoints. The case study results indicate that SAR-based read-across can be refined and strengthened by considering MOAs or proposed reactive metabolite formation pathways, which can improve the overall accuracy, consistency, transparency, and confidence in evaluating analogue suitability.