Sodium alkyl sulphate

Toxicity to other aquatic organisms

Additional information

Two comprehensive stream mesocosm studies are available for two read-across substances belonging to the category of alkyl sulfates: C12AS Na (CAS 151-21-3) and C14-15AS Na (CAS 68081-98-1).

 

An ecosystem - level NOEC for C12AS was determined in a flowing stream mesocosm that was continuously fed water from a high -quality natural stream in southwestern Ohio (the Lower East Fork of the Little Miami River). Stream channels were naturally colonized by algae and invertebrates for 22 -71 days, depending upon substrate, prior to dosing. Six stream channels were dosed with the test substance at nominal concentrations of (control) 0, 26, 78, 233, 700 and 2100 μg active ingredient/L for an additional 56 days. Mean measured concentrations, based on sampling at least once per week, were: Control 0, 20, 61, 224, 582, and 1586 μg active ingredient/L. The mean measured active C12AS concentrations were 76 -96% of nominal. Periphyton and invertebrate communities were extensively sampled prior to dosing and 7, 14, 28, 42, and 56 days after dosing. The 56 -d exposure to C12AS was accompanied by detailed investigations of periphyton community function (autotrophy, heterotrophy, and metabolism of test chemical), periphyton structure (algal population and community dynamics based on taxonomic identity), protozoan structure, and invertebrate structure (benthic abundance, drift, and insect emergence patterns based on taxonomic identity). Single species, caged fish were evaluated in companion studies in the ESF but are not represented in this study summary. The ecosystem-level NOEC is an integrated assessment of all available information. Results of all structural and functional endpoints for both periphyton and invertebrate communities were included when calculating the 56 -day, ecosystem -level toxicological NOEC, which was 224 μg/L (mean measured C12AS). This toxicological ecosystem NOEC was based on reductions in numerical abundance of the mayfly species Stenonema and the stoneflies Plecoptera at >582 μg/L. However, these responses may have been another artifact of bacterial proliferation on the substrate. The decreases observed for Plecoptera and Stenonema were possibly related to their inability to find exposed substrate with swift flow. As such, this NOEC may be viewed as conservative. Further, this value is protective of significant decreases observed for Corbicula abundance at 1585 μg/L. Bacteria proliferated from the C12AS energy subsidy. A nutritional subsidy response of 61 μg/L associated with community changes from C12AS mineralization was determined, which represents nutritional effects related to alteration in food and exposed substrate availability. The toxicological NOEC is considered the final ecosystem NOEC because it relates to the direct toxicity to organisms. A low or no assessment factor, which incorporates uncertainty and the degree of extrapolation of laboratory results to the field, can be applied to the model toxicological ecosystem -level NOEC of 224 μg/L, in evaluating C12AS risk to sensitive aquatic organisms.

 

Moreover, a comprehensive stream mesocosm study is available with a surfactant that was composed of tetra- (C14) and pentadecyl (C15) chain lengths (C14 -15AS). An ecosystem-level NOEC for C14 -15AS was determined in a flowing stream mesocosm that was continuously fed water from a high -quality natural stream in southwestern Ohio, USA (the Lower East Fork of the Little Miami River). Stream channels were naturally colonized by algae and invertebrates for 55 days (May-July 1997) prior to dosing. Four stream channels were dosed at mean measured concentrations of Control, 57, 106, 222, and 419 μg/L (mean measured active C14 -15AS concentrations were 84 -91% of nominal) for an additional 56 days (July-September 1997). Periphyton and invertebrate communities were extensively sampled prior to dosing, and 14, 28, 42, and 56 days after dosing. Results are based on measured concentrations. The 56-d exposure to C14-15AS was accompanied by detailed investigations of periphyton community function (autotrophy, heterotrophy, and metabolism of test chemical), periphyton structure (algal population and community dynamics based on taxonomic identity), and invertebrate structure (benthic abundance, drift, and insect emergence patterns based on taxonomic identity). Single species, caged fish were evaluated in companion studies in the ESF but are not represented in this study summary. Results of all structural and functional endpoints for both periphyton and invertebrate communities were included in calculating the 56-day, ecosystem-level NOEC of 106 μg/L (mean measured C14-15AS). The ecosystem-level NOEC is an integrated assessment of all available information. A higher no-observed-effect-concentration (NOEC) of 222 μg/L was determined for several individual algal and invertebrate species based on univariate statistical analyses. A multivariate analysis based on principal response curves (PRC) indicated that communities in streams exposed to 222 to 419 μg/L were significantly different from the controls, leading to an overall (multivariate and univariate) conclusion that 106 μg/L was the ecosystem NOEC. An apparent energetic subsidy from C14–15AS at the highest concentrations of 222 to 419 μg/L was observed and linked to changes in microbial community processing of AS at these concentrations. A low or no assessment factor, which incorporates uncertainty and the degree of extrapolation of laboratory results to the field, can be applied to the model ecosystem-level NOEC of 106 μg/L in evaluating C14-15AS risk to sensitive aquatic organisms. No assessment factor is needed because the duration of the exposure was long relative to chronic studies, the system contained sensitive flora and fauna, replication was high resulting in statistical sensitivity for key endpoints, ESF communities were highly representative of natural communities, a deep understanding of chemical exposure was developed, and results were consistent with expectations from chronic toxicity studies and species sensitivity distribution analysis.