Cobalt molybdate

Long-term toxicity to fish

Description of key information

NOEC (16d, survival) = 0.22 mg cobalt molybdenum oxide/L (Brachydanio rerio) (read-across from cobalt chloride hexahydrate)

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.22 mg/L

Additional information

No data on long-term toxicity to fish 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 fish (n= 21) are summarised in the WHO CICAD, 2006 (see attached table).

Chronic data for several different fish species were extracted and used in the effects assessment. The NOEC/L(E)C10 values for fish range from 60 μg Co/L for Brachydanio rerio to 2000 μg Co/L for Pimephales promelas (WHO CICAD, 2006), resulting in recalculated values from 0.22 to 7.43 mg cobalt molybdenum oxide/L. The most sensitive data for Brachydanio rerio are reported in detail as key study record (Dave and Xiu, 1991). In this study conducted to methods comparable to guidelines, a NOEC (16d) of 60 µg Co/L (tested as cobalt chloride hexahydrate) was obtained for survival, equivalent to 0.22 mg cobalt molybdenum oxide/L. Further results from studies on other freshwater fish are comprised in the attached table.

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

Molybdenum

Freshwater:

Two studies have been identified that report chronic effect levels for the rainbow trout Oncorhynchus mykiss and produced high-quality effects data (Davies et al., 2005; Parametrix, 2008). The first study reported NOEC values for survival as effect parameter, whereas the second study presented NOEC- and EC₁₀-values for survival and biomass growth. Comparable effect levels (NOECs) were found for survival in both studies. Biomass growth, however, was found to be a more sensitive effect parameter than survival. EC₁₀-values were available based on a single test and on the combined effect-concentration relationship of two tests. Arguments can be put forward why a specific test result should be preferred over the other value. On one hand, combining two tests implies mixing the outcome of test results that were obtained with to different batches of organisms. The normalised effect-concentration relationship, however, shows a clear decrease from 0% effect to >95% effect. Consequently, the confidence interval that is associated with the combined data set is also narrower than the confidence interval around the EC₁₀of the second test, as only small but significant effects (10-22%) were observed at the two highest effect levels. From a conservative point of view, it was decided to use the EC₁₀-value of 43.2 mg Mo/L for assessment purposes.

For the fathead minnow Pimephales promelas two reliable studies were identified: Canton et al. (2006) and Parametrix (2007). High quality data values were available for three endpoints, with (biomass) growth being more sensitive than survival in both studies. As EC₁₀-values are preferred over NOEC-values for risk assessment purposes, the geometric mean of 60.2 mg Mo/L (EC₁₀-values of 39.9 and 90.9 mg Mo/L) was selected as chronic no-effect value for P. promelas. 

A 20-week test with Oncorhynchus kisutch obtained a NOEC of > 19.5 mg Mo/L (m), based on mortality, deformations and hatching percentage (Ennevor, 1993), and a 12-month study conducted with Oncorhynchus mykiss led to a NOEC of > 17 mg Mo/L (m), based on mortality, growth, hematocrits and development of eggs (McConnell, 1977).

 

Marine Water:

One reliable study has been identified for the marine environment, conducted with the sheepshead minnow Cyprinodon variegatus (Parametrix, 2009). Dry weight was the most sensitive endpoint (other endpoints: embryo/larval survival, biomass). For this endpoint a reliable 28d-EC₁₀ of 84.1 mg Mo/L has been reported, and this value is used for assessment purposes.

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.