Cobalt molybdate

Long-term toxicity to aquatic invertebrates

Description of key information

EC50 (28d) = 0.011 mg cobalt molybdenum oxide/L for Hyalella azteca (growth) (read-across from cobalt chloride hexahydrate)
NOEC (28d) = 0.011 mg cobalt molybdenum oxide/L for Daphnia magna (reproduction) (read-across from cobalt sulfate)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.011 mg/L

Additional information

No data on long-term toxicity to aquatic invertebrates 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 chronic single-species toxicity tests resulting in high quality NOEC/L(E)C10 values (expressed as Co) for freshwater invertebrates (n=4) are summarised in the WHO CICAD, 2006 (see attached table).

Chronic data for two different species were extracted and used in the effects assessment. The 21-day LC50 values (mortality) for Daphnia magna range from 21 μg Co/L, tested as cobalt chloride hexahydrate (Biesinger & Christensen, 1972) to 30 μg Co/L, tested as cobalt sulfate (WHO CICAD, 2006), resulting in recalculated values from 78 to 111 µg cobalt molybdenum oxide/L.

More sensitive values were available as NOECs (reproduction) for Daphnia magna (21d and 28d) and Ceriodaphnia dubia (7d), and ranged from <3 to 13 for C. dubia (unknown cobalt compound) and 30 to 50 µg for D. magna (unknown cobalt compound), respectively, with the most reliable NOEC(28d) of 3 µg Co/L, tested as cobalt sulfate with D. magna (WHO CICAD, 2006). The latter NOEC would result in a value of 11 µg cobalt molybdenum oxide/L.

In the key study conducted according to methods comparable to guidelines, the effects of cobalt chloride hexahydrate on Hyalella azteca were investigated and resulted in an EC50 (28d) of 2.9 µg Co/L for growth (Norwood, 2007), equivalent to 11 µg cobalt molybdenum oxide/L.

Further results for other aquatic invertebrates are available and comprised in the attached table.

 

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

Molybdenum

Freshwater:

For the rotifer Brachionus calyciflorus the 48h-EC₁₀value of 193.6 mg/L is retained for assessment purposes (De Schamphelaere et al., 2008). EC₁₀values 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). High quality data 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 assessment purposes.

For the midge Chironomus riparius the 14d-EC₁₀value of 121.4 mg/L is retained (De Schamphelaere et al., 2008). EC₁₀values 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 high quality effects data: GEI (2009), Rodriguez (2007) and De Schamphelaere et al. (2008a). Each of these studies reported 21d-EC₁₀values 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 forD. magna for assessment purposes. 

Author, year	Species	Endpoint	Value [mg Mo/L]
De Schamphelaere et al., 2008	Daphnia magna	21 d NOEC (reproduction) EC10 (reproduction)	112 105.6
GEI, 2006	Daphnia magna	21 d NOEC (reproduction)  EC10 (reproduction)	96.3 - 192.3 108
Rodriguez, 2007	Daphnia magna	21 d NOEC (reproduction) EC10 (reproduction)	49.9 62.8
De Schamphelaere et al., 2008	Ceriodaphnia dubia	7 d NOEC (reproduction)  EC10 (reproduction)	97.3 78.2
GEI, 2006	Ceriodaphnia dubia	21 d NOEC (mortality)	156.5 - 161.5
		21 d EC10 (reproduction)	50.8
De Schamphelaere et al., 2008	Brachionus calyciflorus	48 h NOEC (reproduction)  EC10 (reproduction)	244 193.6
De Schamphelaere et al., 2008	Chironomus riparius	14 d NOEC (growth rate)  EC10 (growth rate)	393 121.4

 

Hence, the NOEC for freshwater invertebrates ranges from 49.9 to 393 mg Mo/L, and the EC10 ranges from 50.8 to 193.6 mg Mo/L.

 

Marine:

A reliable 20d-EC₁₀of 7.96 mg Mo/L has been generated for the marine copepod Acartia tonsa (Aquasense, 2009). EC₁₀ values are preferred over NOEC values as the latter are test design-dependent values. In this specific case the 20d-EC₁₀ is markedly lower than the 20d-NOEC of 26 mg Mo/L. The reported EC₁₀ for A. tonsa is used for assessment purposes. A chronic 28d-growth and reproduction test has been conducted with the marine mysid shrimp Americamysis bahia (Lehman, 2010). No significant effects were noted at the highest exposure concentration level of 116 mg Mo/L (mean measured value). Evaluated endpoints were survival (first and second generation), reproduction (time of first brood, interbrood time, number of young produced per female), and growth (length and dry weight of male and female adult first generation organims). The unbounded value of 116 mg Mo/L is considered as a reliable and conservative NOEC-value for A. bahia.

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.