Microbial catabolism-based grouping enables read-across of non-persistency for all constituents of hexyl glucoside and 2-ethylhexyl glucoside

Alkyl polyglucosides are nonionic surfactants consisting of a hydrophobic alkyl chain and a hydrophilic (oligo)saccharide moiety linked through a glucosidic bond. Ready biodegradability of hexyl glucoside (multi-constituent) and 2-ethylhexyl glucoside (multi-constituent) was demonstrated in Closed Bottle tests (OECD 301D) inoculated with river water. Read-across was used to assess the non-persistency for all constituents of the multi-constituent surfactants. To enable catabolism-based grouping bacteria were isolated from river water using hexyl glucoside (multi-constituent), 2-ethylhexyl glucoside (multi-constituent), hexyl-β-maltoside, glucose, and maltose as sole source of carbon and energy. The first step in the biodegradation of all constituents of hexyl glucoside and 2-ethylhexyl glucoside was cleavage of the glucosidic bond resulting in stoichiometric formation of hexanol and 2-ethylhexanol, respectively. Hydrolysis products formed were mineralized by the isolates or excreted and subsequently metabolized by other microorganisms. Complete degradation of alkyl polyglucosides was achieved by a consortium of microorganisms. Read-across of ready biodegradability and herewith non-persistency for all constituents of hexyl glucoside (multi-constituent) and 2-ethylhexyl glucoside (multi-constituent) is justified based on: the broad substrate specificity of glucosidases in the first biodegradation step resulting in stoichiometric formation of alcohols and the subsequent rapid mineralization of the formed hydrolysis products.