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Long-term toxicity to fish

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Five key studies are presented. In the first study (Pickering and Thatcher 1970; van de Plassche et al 1999), fathead minnows were exposed to concentrations of 0.34, 0.63, 1.2 and 2.7 mg/L LAS in continuous flow systems for a total of 196 days. Each of the four test concentrations plus control received 12 randomly assigned fish obtained from ponds at the Newtown Fish Farm, Ohio Division of Wildlife. Pieces of half-tile were placed in each 10-gallon aquarium for spawning sites. After spawning had been completed, the cluster of eggs was removed and counted. Four replicates of 100 eggs from each concentration were reared for 14 days and mortality of eggs and fry recorded daily. Results indicate that lethality of LAS to newly hatched fry was the most critical factor found. The 196 day NOEC level (normalized to C11.6LAS, van de Plassche et al 1999) was 0.63 mg/L. The LOEC was 1.2 mg/L.

In a second study (Chattopahyay and Konar 1985; van de Plassche et al 1999), the long-term toxicity of the test substance to fish was determined using Tilapia mossambica (tilapia). Groups of 15 fish were exposed to concentrations of 0.0, 0.25, 0.38, 0.51, and 1.10 mg/L for 90 days. Test solutions were renewed every 15 days. The feeding rates decreased significantly at 0.25, 0.38 and 1.10 mg/L. In addition, fish showed erratic behaviour, irregular opercular movement, and at higher concentrations, blood exuded from the base of the pectoral and pelvic fins and head. No apparent difference in condition factor (K) was observed at any concentration. The maturity index (MI) of both male and female fish appeared to decrease at all concentrations, but the biological significance of this is questionable. Fecundity decreased at 0.51 mg/L but not at 1.10 mg/L. The gastrosomatic index (GSI) was significantly different at 0.51 and 1.10 mg/L. Based on the most reliable endpoints (GSI and fecundity), the NOEC would be 0.38 mg/L and the LOEC would be 0.51 mg/L. However, in view of certain reporting limitations as described in the dossier, and the fact that previous evaluations of this study have reported a NOEC of 0.25 mg/L (van de Plassche et al., 1999), a conservative (protective) NOEC for this study is considered to be 0.25 mg/L and the LOEC considered to be 0.51 mg/L.

In the third long-term study (Canton and Slooff 1982; van de Plassche et al. 1999), groups of 50 guppies (Poecilia reticulata) were exposed to various concentrations of LAS for 28 days. Test solutions were renewed three times per week. The only effect (98% mortality at 10 mg/L) occurred within 2 days of study initiation. The 28 day NOEC normalized by van de Plassche et al. (1999) to C11.6LAS was 3.2 mg/L. The 28 day LOEC was 10 mg/L.

In another study (Unilever 2010), fertilized eggs of rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) were exposed to mean measured concentrations of 0.03, 0.23, 0.35, 0.63, 0.95 and 1.9 mg/L, for 72 days. The responses recorded included the survival of eggs, time to eyed egg stage, time to hatch, survival and final weight of sac-fry (eleutheroembryos), and time and extent of swim-up (external feeding). The lowest NOEC value found was 0.23 mg/L based on survival of eggs exposed from eyed stage, survival of eggs exposed from fertilization, survival of sac fry, and overall survival from fertilization to swim-up. The data are for C11.6LAS and no normalization is required.

Finally, a long term toxicity test (Maki 1981) to juvenile bluegills (Lepomis macrochirus) was conducted on C12LAS. Fish growth was determined after 28 days exposure in a flow-through model ecosystem to measured concentrations of 0, 0.5, 1.0, 2.0, and 4.0 mg/L. Results showed that the growth of juvenile bluegills was not affected at 0.5 and 1.0 mg LAS/L, but was reduced at 2.0 and 4.0 mg/L. At the end of the exposure period, fish at 1.0 mg/L LAS had a biomass of 44 gm/m2compared to 10.5 gm/m2for the 2.0 mg/L concentration. Based on these effects on growth rate, the NOEC was 1.0 mg/L.

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