Cobalt sulphate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

1.06 µg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

2.36 µg/L

Assessment factor:

3

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

0.37 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

53.8 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

69.8 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

10.9 mg/kg soil dw

Assessment factor:

2

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Conclusion on classification

For classification purposes, Ecotoxicity Reference Values (ERVs) should be derived using the “lowest value” approach. For metals ERVs are derived using data from one or more soluble metal substances, and in most cases, test data are reported on a “dissolved” metal concentration basis. In the assessment for Co, the aquatic toxicity classifications of Co metal and Co compounds are derived by comparing the quantity of dissolved Co liberated during an OECD Transformation/Dissolution test (OECD 29) with the ERVs derived from laboratory toxicity tests developed with a soluble cobalt compound (e.g. cobalt dichloride). In the case of Co, single acute and chronic ERVs are available without consideration of factors that might affect Co bioavailability or toxicity (i.e. pH, DOC, hardness).

 

The acute ERV is based on available ecotoxicity data for an plant species, Lemna minor, while the chronic ERV is based on available ecotoxicity data for the epibenthic invertebrate, Hyalella azteca. The reported Co ERVs are as follows:

           Acute:            Lemna minor             52.0μg/L

           Chronic:         Hyalella azteca         7.6μg/L

 

As outlined in the CLP guidance (ECHA 2017), substance-specific ERVs can be developed using the following equation:

ERVsubstance = ERVCo × MWsubstance / (n × MWCo)

where n is the stoichiometric number of Co atoms in the substance molecule.

A full description of ERV derivation is provided as attachment to endpoint summary of IUCLID section 6.

The EU CLP guidance document (ECHA 2017) permits consideration of the “environmental transformation” of metals in the environment, including removal from the water column and deposition and sequestration in sediments, much the same way as the concept of “rapid degradation” is considered for organic chemicals. To indicate “rapid removal” for a metal, it is assumed that one must demonstrate greater than 70% removal of soluble metal within 28 days of addition to the water column, as is the case with organic compounds. Furthermore, one must demonstrate that the potential for metal remobilisation from sediments is limited, for example by changes in metal speciation, remineralisation and permanent burial in the sediment. If these conditions are met, the metal is considered “rapidly removable” and poses lower chronic environmental risk. Results of modelling using the Unit World Model (UWM) and initial empirical testing via the extended transformation/dissolution protocol (e-TDp) indicate that the cobalt ion satisfies the requirements for “rapid” metals removal, i.e. > 70% removal from the water column in 28 days, and the limited sediment remobilisation potential under most environmental conditions.

Water solubility is 124.7 g Co/L at 20C

Expected to be readily soluble under TDp as well

Molecular weight is 154.99 g/mol

Substance-specific ERVs are:

Acute ERV: 136.8 μg/L– <1mg/L so Acute 1

Chronic ERV: 20.0 μg/L– between 10 and 100μg/L so Chronic 1 (M=1) or Chronic 2 depending on rapid removal

Proposed self-classification:

Acute 1 (M = 1) and Chronic 2