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Persistent, Bioaccumulative and Toxic (PBT) and very Persistent and very Bioaccumulative (vPvB) are regulatory hazard categories that have been set to manage the possible risks to humans and the environment from these chemicals. In industrial chemicals regulations, their aquatic Bioaccumulation potential is usually assessed first with a screening based on the octanol/water partition coefficient (K ow). However, current log K ow cut-off values triggering classification, categorisation and/or further fish bioconcentration testing are not harmonised worldwide, and they have never been assessed for their regulatory relevance. In this study, the experimentally determined log K ow and fish bioconcentration factors (BCF) of 532 chemicals were compared. While the analysis underlined the robustness of using log K ow as a screening tool (5/532 were false negatives; log Kow: non-bioaccumulative, but BCF: bioaccumulative), it also demonstrated the conservatism of the cut-offs used worldwide. Indeed, many chemicals were deemed potentially Bioaccumulative based on log K ow when a fish bioaccumulation test showed no concern (false positives), therefore, leading to unnecessary use of vertebrate animals. Our analysis shows that the log Kow cut-off could be increased to 4.5 in all regions for all purposes without leading to a reduced protection of humans and the environment. [Display omitted] • Log Kow bioaccumulation underestimated only 5/532 chemical (false negatives). • In this analysis, all false negatives contained multi-cyclic groups and/or halogens. • Cut-offs <4 for in vivo testing are overconservative (false positives). • Cut-offs for potentially B/vB are conservative and could be increased to 4.5 • Structural rules could maybe be applied where hydrophobicity is not the driver. [ABSTRACT FROM AUTHOR]