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Data generated with sodium methanethiolate are used for assessing the aquatic ecotoxicity for methanethiol.

Freshwater zebra fish (Danio rerio) were exposed to nominal concentrations of 0, 0.95, 1.7, 3.1, 5.6 and 10 mg

sodium methanethiolate active ingredient (a.i.)/L for 96 hours in an acute study performed according to the OECD TG 203 and EEC Method C.1 under semi-static conditions (Gancet et al., 2004a). Mean analytical concentrations were 0, 0.11, 0.53, 1.74, 4.98, and 7.84 mg a.i./L, respectively. Mortality was 100% at the two highest concentrations and 30% at the 1.74 mg/L concentration after 96 hours. During the study, there were no abnormal behavioral signs in the controls or treated fish. By the end of the study, some fish in the higher concentration test groups displayed signs such as red gills and reduced mobility. The 96-hr LC50, based on mean measured concentrations was 1.8 mg/L and therefore the substance is considered as toxic to fish.

Daphnia magna were exposed to sodium methanethiolate at nominal concentrations of 0.6, 1.0, 1.7, 2.9 and 5.0 mg a.i./L for 48 hours in an OECD TG 202 study using a static design (Elf Atochem, 2000). The initial measured concentrations ranged from 0.83 to 7.47 mg a.i./L. Immobility was 100% at the three highest concentrations, whereas no immobility was observed at 0.6 mg/L (nominal) and 10% immobility occurred at 1.0 mg/L (nominal). The EC50range (1.32-2.46 mg/L) was based on measured concentrations

and therefore the substance is considered as toxic to Daphnia.

Pseudokirchneriella subcapitata were exposed to sodium methanethiolate for 72 hours at nominal concentrations of 0, 0.5, 1, 5, 10, 50 and 100 mg a.i./L in a test conducted according to OECD TG 201 (Gancet et al., 2004b). Cell density was significantly reduced at the nominal concentrations of 10, 50 and 100 mg/L. The measured concentrations were 0, 0.63, 1.13, 5.95, 10.96, 48.12 and 87.81 mg a.i./L on Day 0 and 0, 0.33, 0.59, 2.84, 4.96, 20.48, and 35.31 mg a.i./L at 72 hours. The 72-hr EC50was 6.3 mg/L for biomass and 15 mg/L for growth rate. The corresponding 72-hr NOECs were 0.81 (biomass) and 4.11 mg/L (growth rate). All effect values were based on mean measured concentrations

and therefore the substance is considered as harmful to algae.