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Ecotoxicological information

Toxicity to soil macroorganisms except arthropods

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Description of key information

A total of ten topsoils with contrasting properties that may affect the toxicity of Mo in soil were used for testing two toxicity assays with annelid worms (reproduction for Enchytraeus crypticus and Eisenia andrei) after spiking with sodium molybdate. In addition, an OECD artificial soil was also tested. The annelid toxicity assays resulted in twenty individual high-quality NOEC/EC10 selected for PNEC derivation. The NOEC/EC10 values ranged from 7.88 to 1661 mg added Mo/kg dry weight soil.

Additionally, three soils were aged outdoors after spiking with sodium molybdate. After 6 and 11 months, subsamples were collected and the same ecotoxicity tests as above were conducted on these soils. In general, this showed that long-term equilibration of Mo in soils decreases its toxicity to annelids. The results of the toxicity in aged soils are used to determine a Leaching/Ageing factor to correct for the effect of spiking on the toxicity of Mo in soil organisms.

Key value for chemical safety assessment

Additional information

Invertebrate toxicity assays with other soil macro-organisms (Enchytraeus crypticus and Eisenia andrei) resulted in twenty individual high quality NOEC/EC10 values which were also used for PNEC derivation purposes. The selected NOEC/EC10 values range from 7.88 mg added Mo/kg (E. andrei) to 1661 mg added Mo/kg (E. crypticus). All data are based on added measured Mo concentrations in dry weight soil. For E. crypticus, a number of unbounded NOEC values were also observed, i.e. with no effects at thr highest test concentration (EC10> 2719 and 2816 mg added Mo/kg dw soil respectively). For the aged soils, the comparison of Mo in freshly spiked and 11-month aged soils show that long-term equilibration of Mo in soils generally decreases its toxicity to invertebrates. Only in one case (out of six cases) an effect at a lower dose was observed in the aged soil (E. crypticus). The results of the toxicity in aged soils are used to determine a Leaching/Ageing factor to correct for the effect of spiking on the toxicity of Mo in soil organisms.