Enabling dual hazard assessment for single-chain polychlorinated n-alkane mixtures at environmentally relevant levels: a proof of concept

Chlorinated paraffins (CPs) are widely used industrial substances composed of complex mixtures of polychlorinated n-alkanes (PCAs). Regulatory classification typically groups CPs into short-, medium-, and long-chain categories, yet this grouping does not reflect the composition of current commercial products and complicates hazard assessment and regulation. Here, we present the first dual-endpoint aquatic hazard assessment of one of the most dominant single-chain PCA mixtures (C 14 , 55% Cl) present in commercial mixtures, tested at environmentally realistic concentrations using passive dosing. Using this approach, biodegradation and aquatic toxicity can simultaneously be assessed in lake and municipal wastewater effluent systems. Over time, microorganisms decreased the concentrations of the PCA-C 14 in the water phase, with chlorine-content-dependent degradation and fitted half-lives of approximately two days. In contrast, no decline was observed in abiotic controls or in the solid phase. Concomitant increases in total organic carbon and chemical oxygen demand further support the presence of microbial transformation. This proof-of-concept study demonstrates that simultaneous degradation and toxicity testing of single-chain PCA mixtures is feasible under environmentally realistic conditions and offers a foundation for further refinement of persistence and hazard evaluation for PCAs.