Cobalt molybdate

Toxicity to terrestrial plants

Description of key information

EC10 (21d) = 3.7 mg cobalt molybdenum oxide/kg soil dw (Brassica napa) for shoot biomass (read-across from cobalt chloride)
EC50 (21d) = 25.9 mg cobalt molybdenum oxide/kg soil dw (Brassica napa) for shoot biomass (read-across from cobalt chloride)

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:

25.9 mg/kg soil dw

Long-term EC10, LC10 or NOEC for terrestrial plants:

3.7 mg/kg soil dw

Additional information

No data on toxicity to terrestrial plants are available for cobalt molybdenum oxide. However, there are reliable data available for different structurally analogue substances.

The environmental fate pathways and ecotoxicity effects assessments for cobalt metal and cobalt compounds as well as for molybdenum metal and molybdenum compounds is based on the observation that adverse effects to aquatic, soil- and sediment-dwelling organisms are a consequence of exposure to the bioavailable ion, released by the parent compound. The result of this assumption is that the ecotoxicology will be similar for all soluble cobalt and molybdenum substances used in the ecotoxicity tests. Therefore, data from soluble cobalt and molybdenum substances are used in the derivation of ecotoxicological and environmental fate endpoints, based on the cobalt ion and molybdenum ion, respectively.

Cobalt

Data on terrestrial plants toxicity tests resulting in high quality EC10 and EC50 values (expressed as Co) for terrestrial plants (n=3) are summarised in the WHO CICAD (2006). The key study however, is not included in this document.

This study conducted according to ISO 11269-2 (ISO 1995) investigated the toxicity of cobalt chloride to three plants in 10 different soils, with the overall lowest EC10 (21d) value for Brassica napa of 1 mg Co/kg soil d.w. corresponding to 3.7 mg cobalt molybdenum oxide/kg soil d.w. (Li et al., 2009). The range of EC10 values in the study varied from 1 mg Co/kg soil d.w. for Brassica napa and Lycopersicon esculentum to 617 mg Co/kg soil d.w. for Hordeum vulgare. The corresponding lowest EC50 was reported as 7 mg Co/kg soil d.w. corresponding to 25.9 mg cobalt molybdenum oxide/kg soil d.w. Generally, a higher sensitivity to cobalt was observed in soils of lower pH. Brassica napa was the most sensitive species, followed by Lycopersicon esculentum and least sensitive was Hordeum vulgare.

Two other studies report EC20 values based on growth of Medicago sativa, Hordeum vulgare and Raphanus sativus which ranged from 0.6 to 45.2 mg Co/kg soil d.w., with citrus fruits showing no effect concentrations <100 mg Co/kg soil d.w. (WHO CICAD, 2006). The overall range corresponds to EC20 values of 2.2 to 371 mg cobalt molybdenum oxide/kg soil d.w.

References: World Health Organization (2006). Concise International Chemical Assessment Document 69. COBALT AND INORGANIC COBALT COMPOUNDS.

Molybdenum

For plants, in total 45 individual high quality EC10 values (for 5 different plant species) are selected, 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.

Author, year	Species	Endpoint	Value [mg Mo/kg soil dw]
Micò et al., 2010	Lolium perenne	21 d EC10	14 - 3476
Micò et al., 2010	Hordeum vulgare	21 d EC10	3 - 433
Kàdàr, 1995	Zea mays	4 d EC10	20
Micò et al., 2010	Brassica napus	21 d EC10	4 - 2844
Micò et al., 2010	Trifolium pratense	21 d EC10	0.4 - 1502
Micò et al., 2010	Lycopersicon esculentum	21 d EC10	3 - 1575
Biacs et al., 1995	Daucus carota	6 mo EC10	>= 114
Nyàrai-Harvàth, 1997	Pisum sativum	3 mo EC10	>= 114

 

Conclusion
As the effect values derived from analogue cobalt compounds are considerably lower than those derived from analogue molybdenum substances, it can be reasoned that the cobalt ion will account for the effects in ecotoxicological testing. Hence, it was concluded to put forward the most sensitive and reliable results derived from analogue cobalt compounds for assessment purposes, and recalculate them for CoMoO4.