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Sediment toxicity

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Key value for chemical safety assessment

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Reliable studies (Klimisch 1 or 2) on toxicity of arsenic substances to sediment organisms are not available. According to ECHA Guidance on information requirements and chemical safety assessment (Chapter R.10.5.2), in the absence of ecotoxicological data for sediment-dwelling organisms, the PNEC for freshwater sediment can be derived from the PNECfreshwater and the partitioning coefficient (Kp) for solids-water in suspended matter using the equilibrium partitioning method:

PNECfreshwater sediment (mg As/kg dw) = PNECfreshwater (0.013 mg As/L) * Kp suspended matter (L/kg dw)

A log Kp of 4.0 was selected for suspended matter in freshwater and marine systems based on the 50thpercentile of log Kp values for 25 water systems (log Kp values range from 2.0 to 6.0). This results in a PNECfreshwater sediment of 130 mg As/kg dw. This PNEC for freshwater sediment is protective as it is well below toxic As concentrations in laboratory-spiked freshwater sediments. In a laboratory study (Visviki et al, 2006; Klimisch 4), the LC 50 for 10-d survival of L. plumulosus in spiked natural sediments is 800µg As/L.Applying a log Kp value (solids-water in suspended matter) of 4.0, this LC50 corresponds to 8000 mg As /kg dw sediment.