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Ecotoxicological information

Toxicity to terrestrial plants

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A total of 10 topsoils with contrasting properties that may affect the toxicity of Mo in soil were collected and on each of these soils a series of 5 plant assays (root elongation for barley and shoot yield for Oilseed rape, Red clover, Ryegrass and Tomato) were performed after spiking with sodium molybdate.  
The plant toxicity assays resulted in 45 individual high quality EC10 values selected for PNEC derivation. The EC10 values ranged from 4 to 3476 mg added Mo/kg dry weight soil.
Additionally, 3 soils were aged outdoors after spiking with sodium molybdate. After 6 and 11 months, subsamples were collected and the 4 ecotoxicity tests (same as above without barley root elongation assay) were conducted on these soils. In general, this showed that long-term equilibration of Mo in soils decreases its toxicity to plants. 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

For plants, in total 45 individual high quality EC10 values (for 5 different plant species) are selected for the PNEC derivation, ranging from 4 mg added Mo/kg dw (for oilseed rape in soil 10 and red clover in soil 9) to 3476 mg added Mo/kg dw (for ryegrass in soil 1).

All data are based on added measured Mo concentrations in soil.

For 5 dose-response-curves, no reliable EC10 or NOEC could be derived because a significant effect was already seen at the lowest dose tested (oilseed rape and red clover shoot yield in soil 7, tomato shoot yield in soil 10 and barley root elongation in soils 2 and 10).

For the aged soils (soil 4, 5 and 6), the comparison of Mo in freshly spiked and 11 -month aged soils show that long-term equilibration of Mo in soil generally decreases its toxicity in plants. Only in one case (out of 12 cases) there was an effect at a lower dose in the aged soil (oilseed rape in soil 4). The results of the toxicity in aged soils is used to determine a leaching/ageing factor to correct for the effect of spiking on the toxicity of Mo in soil organisms.