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Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

General considerations

CdZnS is a highly insoluble Cd-compound. This is demonstrated by the transformation-dissolution tests, where after 7 days shaking at pH6 only 0.06% of the Cd in the substance goes into solution; after 28 days of testing, dissolution was still very low: 0.23% of total Cd contained in the substance. For this reason, the ecotoxicity results obtained on soluble Cd-compounds are considered not relevant for CdZnS. Reference is made to standardised testing, applied on CdTe, another Cd-compound with limited solubility in water. The solubility of CdTe is however higher than the one of CdZnS, so this dataset on CdTe can be considered as a worst case for the CdZnS.

For PNEC derivation, a basic assumption made in this hazard assessment and throughout the CSRs on cadmium and cadmium compounds, (in accordance to the same assumption made in the EU RA process), is that the causative factor for ecotoxicity of these substances is the Cd++ion. As a consequence, for the setting of PNEC's for these substances, the generic PNEC as derived for the Cd++ion is used, and is always referring to the Cd ion concentration.

However, Cd-substances can differ significantly in their solubility, i.e. their capacity to release cadmium ions into (environmental) solution. That effect is checked eventually in the transformation/dissolution (T/D) tests and may result in different environmental hazard and, consequently, different classification for aquatic effect.

Classification

CdZnS is specifically excempted from classification under DSD 67/548/EEC.The reason for this non-classification is the insolubility of the substance.

For CLP, data were generated to check this existing classification against the CLP rules. To this end, transformation/dissolution (T/D) tests were performed on the CdZnS, and reference was made towards newly generated T/D and ecotoxicity data obtained on another sparingly soluble Cd-compound, i.e. CdTe. By comparing T/D data between CdZnS and CdTe, and referring to aquatic effect levels observed for CdTe, the aquatic hazard of the CdZnS could be assessed as follows:

Acute aquatic classification

Standard ecotoxicity testing on CdTe revealed a lowest EC50 value of1.14 mg CdTe/Lobserved forDaphnia magna (resulting in no acute classification of CdTe). T/D testing on CdTe demonstrated the sparingly soluble character of this substance (3.2% of Cd solubilised after 7days in pH 6 medium, which is maximising Cd-solubilisation in the relevant pH range 6 -8.5). The solubility of Cd from CdZnS was however even much lower than the solubility of Cd in CdTe: after 7 days only 0.06 % of the Cd was solubilised from CdZnS at pH 6. Considering a) the lowest EC50 value of CdTe of 1.14mg/l, and b) the 50x lower solubility of Cd in CdZnS, as compared to CdTe, it is concluded that also CdZnS is not classified for acute aquatic effect.

Chronic aquatic classification

Standard ecotoxicity testing on CdTe revealed a lowest NOEC value of 0.2 mg CdTe/L observed forDaphnia magna,resulting in classification as

"chronic 3"of CdTe - in this respect it is noted that Cadmium compounds are considered as being "equivalent to rapidly degradable" based on their rapid removal from the water column, see section 4.6.). T/D testing on CdTe demonstrated the sparingly soluble character of this substance (3.8% of Cd solubilised after 28 days in pH 6 medium, which is maximising Cd-solubilisation in the relevant pH range 6 -8.5). From T/D tests, it was shown that the solubility of Cd from CdZnS was however even much lower than the solubility of Cd in CdTe: after 28 days only 0.23 % of the Cd was solubilised from CdZnS at pH 6. Considering a) the lowest NOEC value of CdTe of 0.2mg/l, and b) the fact that >16 x less Cd solubilizes from the CdZnS as compared to CdTe (in other words, 16x more CdZnS loading (~=0.2 x 16 ~= 3.3 mg/l - would be needed to reach the lowest NOEC value), it is concluded that CdZnS is not classified for chronic aquatic effect.

This analysis confirms the non-classification of CdSSe for aquatic effects under DSD.