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Sediment toxicity

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Description of key information

EC50 (28 d) > 1000 mg a.s./kg dw (Chironomus riparius, EPA OPPTS 850.1790, emergence ratio, nominal)

NOEC (28 d) = 250 mg a.s./kg dw (Chironomus riparius, EPA OPPTS 850.1790, emergence ratio, nominal)

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:
1 000 mg/kg sediment dw
EC10, LC10 or NOEC for freshwater sediment:
250 mg/kg sediment dw

Additional information

One experimental guideline study is available investigating the toxicity of the test item towards freshwater sediment organisms according to GLP. A long-term study was performed with the freshwater species Chironomus riparius (M-303715-01-2) according to OECD 218. First instar of Chironomus riparius larvae, 4 beakers per test concentration, control and solvent control with 20 animals each) were exposed in a static test system for 28 days to initial nominal concentrations of 62.5, 125, 250, 500 and 1000 mg a.s./ kg dw sed (dry weight sediment) of a water-sediment system. The concentration of the active substance Pyrasulfotole was analysed in the freshly prepared spiked sediments of all test concentrations and the controls on day -1. Moreover the test item concentrations were analyzed at day 0 (directly before inserting of the larvae), day 7 and day 28 (after insertion of the larvae) in the overlying water, the pore water of the sediment and the sediment in additionally prepared test vessels. Chemical analyses were performed for the test item for sediment, overlying water and pore water samples. Sediment analyses on day -1 (directly after spiking) reflect high recoveries of the test item with 107 to 121% (mean of 113%) of nominal concentrations in all test levels, thus all results are based on initial nominal concentrations of the test item in the sediment, expressed in mg a.s./kg dw sed. Chemical analyses of the sediment, overlying water and pore water over time reflect the aquatic fate profile the test item with it partitioning out of the sediment into the water column overtime. Analyses of the sediment over time showed decreasing recoveries of 39% to 50% (mean = 46%) of nominal for all test concentrations on day 0. On day 7, 17% to 28% (mean = 23%) and on day 28, 14% to 20% (mean = 17%) of nominal were found, respectively.Analyses of the overlying water over time showed increasing recoveries of 26% to 28% (mean = 28%) of nominal applied amount of a.s. per test concentration on day 0. On day 7, 58% to 64% (mean = 61%) and on day 28, 60% to 72% (mean = 68%) of nominal were found, respectively. Analyses of the pore water over time yielded in decreasing recoveries of 18 % to 20% (mean = 19%) of nominal concentrations on day 0 for all test concentrations. On day 7, 5.6% to 7.6% (mean = 6.7%) and on day 28, 3.0% to 4.5% (mean = 4.1 ) of nominal were found, respectively.Start of emergence was at day 15 to 16 for the controls and in all other test concentrations.91.9% of the inserted (n= 160) larvae maturated to adults in the controls after 28 days, fulfilling the guideline requirements.Statistical tests indicates no statistically different distribution between sexes compared to the assumption of 50% females and 50% males. Therefore male and female results were pooled for further statistical analyses to increase the statistical power. There was a statistical significant difference in emergence at the 500 and 1000 mg a.s./kg dw sed treatment levels as compared to the pooled controls, resulting in a NOEC of 250 mg a.s./kg dw sed. For the development rate (pooled sex) there were no statistical significant differences as compared to the pooled controls up to the highest test concentration, resulting in a NOEC of ≥ 1000 mg a.s./kg dw sed. Allendpoints were evaluated based on the nominal initial concentration of the test item.