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Long-term toxicity to aquatic invertebrates

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Description of key information

Relevant and reliable data that could be used for the determination of a PNEC for the freshwater environment - using the statistical extrapolation method - were retrieved for 5 different species: the rotifer Brachionus calyciflorus, the cladocerans Daphnia magna and Ceriodaphnia dubia, the amphipod Hyalella azteca and the midge Chironomus riparius. Test results were obtained in experiments that followed international accepted guidance, and were based on measured levels of dissolved molybdenum. Values were  193.6 mg Mo/L, 89.5 mg Mo/L, 63.0 mg Mo/L, 44.6 mg Mo/L and 121.4 mg Mo/L, respectively.

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Additional information

Freshwater compartment

For the rotifer Brachionus calyciflorus the 48h-EC10 value of 193.6 mg/L is retained for the derivation of a predicted no-effect concentration for molybdenum (De Schamphelaere et al, 2008). EC10 values are preferred over NOEC values as the latter are test design-dependent values. In this specific case the 48h-EC10 is even more sensitive than the 48h-NOEC of 244 mg/L.

 

For Ceriodaphnia dubia two reliable studies were identified: GEI (2009) and De Schamphelaere et al (2008). K1-values were available for two endpoints, with reproduction being more sensitive than survival. The geometric mean of both studies, 63.0 mg Mo/L, was selected for the derivation of a predicted no effect concentration of molybdenum.

 

For the midge Chironomus riparius the 14d-EC10 value of 121.4 mg/L is retained for the derivation of a PNEC for molybdenum (De Schamphelaere et al, 2008). EC10 values are preferred over NOEC values as the latter are test design-dependent values. In this specific case the 14d-EC10 is more sensitive than the 14d-NOEC of 393 mg/L.

 

For the cladoceran Daphnia magna there were three studies that provided K1 effects data: GEI (2009), Rodriguez (2007) and De Schamphelaere et al (2008a). Each of these studies reported 21d-EC10 values based on reproduction. The geometric mean of 89.5 mg/L that is derived with these three values (62.8, 105.6, 108 mg Mo/L) is put forward for D. magna for the derivation of a PNEC for molybdenum.