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Long-term toxicity to aquatic invertebrates

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A series of studies are used to characterize the long-term toxicity of LAS to aquatic invertebrates. In the first study (Maki 1977; van de Plassche et al 1999), the toxicity of C11.8LAS was evaluated in a 21-day survival and reproduction test with Daphnia magna. Four replicates per concentration, five organisms per replicate, were tested in a flow-through system. Mean measured concentrations were 0.32, 0.59, 1.18, 2.52, and 4.85 mg/L C11.8LAS as active ingredient. Survival was monitored at 24-hr, 96-hr, 7 days and daily thereafter. Reproduction was monitored beginning with the production of the first brood on day 7 or 8, and daily thereafter. Results, based on the mean measured concentration of the active ingredient, indicate that the 21-day NOEC was 1.18 mg/L. The 21 day LC50was 1.67 mg/L, while the EC50s, based on total young production, average brood size, and percent days reproduction occurred, were 1.50, 2.30, and 2.31 mg/L, respectively. These results were then normalized to a C11.6LAS according to the methods of van de Plassche et al. (1999), and the final NOEC value is 1.41 mg/L.

In another study (Taylor 1984; van de Plassche et al 1999), a 7 day chronic toxicity test on C11.8LAS was conducted with Ceriodaphnia sp. under semi-static conditions.Ceriodaphnia were fed either a yeast diet, or an algae/trout chow diet. The test medium was renewed three times in the seven days. Nominal test concentrations were 0, 0.5, 1, 2, 3.5, 5 and 7 mg/L of active ingredient. The resultant 7 day LC50values were 5-7 mg/L for both diets. The no effect concentrations differed between diets. The 7 day NOEC for the yeast diet was 0.5 mg/L (based on reproduction) while the 7 day NOEC for the algae/trout chow diet was 5 mg/L (based on mortality and reproduction). When normalized to a C11.6LAS, the lowest NOEC is 0.59 mg/L.

In the third study (Maki 1978, 1981; van de Plassche et al 1999), effects on the midge were examined. Groups of P. parthenogenica were exposed for 28 days to concentrations of 0.5, 1.0, 2.0, or 4.0 mg/L (nominal) of LAS. The LOEC was 4 mg/L based on survival and reproduction, and the NOEC was 2.0 mg/L. When normalized to C11.6LAS, the NOEC value becomes 2.8 mg/L.

The chronic toxicity of C12.3LAS was evaluated in a 2 day whole life cycle bioassay on the rotifer, Brachionus calyciflorus (Procter & Gamble 1996; van de Plassche et al 1999). Six newly hatched rotifers (<3 hours old) were placed in each replicate beaker, and exposed to C12.3LAS for 48 hours. Results were based on the total number of live, swimming organisms (both adults and offspring) and measured concentrations. The resultant EC10 value was 1.18 mg a.i./L, the EC20was 1.4 mg a.i./L, and the EC50was 2.0 mg a.i./L. When normalized to a C11.6LAS, the EC10 value becomes 1.69 mg/L.

Finally, the chronic toxicity of C12LAS was determined in a 32 day test (Versteeg 2001; Versteeg and Rawlins 2003; van de Plassche et al 1999) with three aquatic invertebrates (Corbicula, Elimia, Hyalella). The invertebrates were caged in the tail pools of an environmental stream mesocosm study of C12LAS. Toxicity was based on water concentrations at which adverse effects were observed. Results were also calculated based on the tissue concentrations at which adverse effects were observed. All invertebrates were exposed to nominal concentrations of 0, 0.15, 0.30, 1.0, and 3.0 mg a.i./L. As mean measured concentrations were 84-99% of nominal, results are based on measured concentrations. On days 0, 8, 16, and 32, the invertebrates were examined for growth and survival. The results can be summarized as follows (all normalized to C11.6): For Corbicula, the 32 day EC20 was 0.39 mg/L based on growth (length), for Elimina, the 32 day NOEC was 4.15 mg/L based on survival and for Hyalella the 24 day EC20 was 1.36 mg/L based on survival.

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