Xylene substances recently received REACH testing decisions requiring extended one-generation reproductive toxicity studies (EOGRTS) with additional developmental neurotoxicity (DNT) cohorts for each of the three isomers. As a legacy chemical with extensive existing animal and human data, xylene offers a strong case for asking whether this further animal testing is truly needed, in line with ECHA’s commitment to the 3Rs.
This weight of evidence review re-evaluated the published literature, including the studies ECHA cited, using current scientific standards. It also included new unpublished guideline studies provided by the Lower Olefins and Aromatics REACH Consortium. Xylene is a well-recognised narcotic: its effects on the central nervous system are transient and fully reversible, working through a non-specific effect on nerve cell membranes. Xylene is rapidly metabolised and excreted within 24 hours, and limited amounts reach the fetus. Nine new guideline studies showed no treatment-related nervous system effects up to 1000 mg/kg bw/day. The historical DNT studies had significant methodological weaknesses, including poor study design, no positive controls and confounding by ethylbenzene.
Across all lines of evidence, no convincing data indicate that xylene causes developmental neurotoxicity. The review concludes that there is no trigger for an additional DNT cohort in an EOGRT study of xylene. Because of how the EOGRTS DNT cohort is designed, it also could not tell transient narcotic effects apart from true developmental effects, so it would produce unreliable data.
Authors
L. G. Higgins, F. Faulhammer, M. Rooseboom, N. Aygun Kocabas, J. H. Arts, A. Cordova, E. Freeman, M. Nahar, E. Richmond, S. Schneider, K. Morris-Schaffer
Society of Toxicology (SOT) Annual Meeting 2025, Neurotoxicity: Developmental II, Board J501, Abstract ID 4664.