Cobalt sulphate

Sediment toxicity

Description of key information

Relevant and reliable data that could be used for classification and PNEC for sediment-dwelling organisms were retrieved for three species: Hyalella azteca, Tubifex tubifex, Lumbriculus variegatus. The toxicity values range from 698 mg Co/kg for H. azteca to >2170 mg Co/kg for L. variegatus. Tests followed international accepted guidance and were based on measured levels of cobalt dichloride.

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:

1 703 mg/kg sediment dw

EC10, LC10 or NOEC for freshwater sediment:

698 mg/kg sediment dw

Additional information

Freshwater:

High quality chronic toxicity tests were identified for three benthic invertebrates. EC10 values ranged from 698 mg Co/kg for Hyalella azteca (OSU 2018) to >2170 mg Co/kg for Lumbriculus variegatus (Nguyen et al., 2009b). Cobalt toxicity (on the basis of EC10 values - mg Co/kg sediment [dry weight] - for the most sensitive endpoint) for the three benthic species can be ranked as follows: H. azteca > T. tubifex > L. variegatus. The following table indicates those EC10 values of high quality that have been carried forward for the HC5 and PNEC derivation. 

Table Selected values for the most sensitive endpoints used for derivation of the freshwater sediment HC5

	Species	Endpoint	Value (mg Co/kg dw)
OSU 2018	Hyalella azteca	Growth: EC10	698
Nguyen et al (2009a)	Tubifex tubifex	Reproduction: EC10	1176
Nguyen et al (2009b)	Lumbriculus variegatus	Survival: EC10	>2170

Available data suggests that cobalt bioavailability is affected by sediment physical: chemical characteristics. No chronic effects of cobalt were observed when SEM_Co/AVS ≤ 1 (SEM_Co-AVS ≤ 0), implying the applicability of the SEM/AVS approach for predicting cobalt sediment toxicity. Additional empirical studies are on-going that will aid in the characterization and quantification of those sediment parameters that affect cobalt bioavailability.

Marine:

Limited reliable acute or chronic toxicity data for the marine sediment compartment were identified in the open literature or grey literature. It was, therefore, decided to derive a PNEC_{sediment, marine} from the previously derived PNEC_{sediment,freshwater}. Because of the observed decreased sensitivity of marine water-column dwelling organisms versus freshwater water-column dwelling organisms, it was felt that the use of the PNEC_{sediment, freshwater} was an environmentally conservative approach that would be protective of the marine environment. Studies are on-going that will validate the acceptability of this assumption.