Concentrates of lead and zinc compounds with sulfur resulting from hydrometallurgy (hot acid leaching, super-hot acid leaching and flotation)

Toxicity to terrestrial plants

Description of key information

According to the transformation/dissolution study (OECD guidance 29) conducted for the substance, the most critical and bioavailable constituents of the target substance are lead and zinc. Therefore, the chemical safety assessment focuses on the properties of these constituents, and the toxicity data for both constituents are taken into account in the CSA, and the PNEC soil is derived for both critical constituents, and used as threshold values in the ES&RC.

Additional information

Because the target substance is an inorganic solid UVCB substance and insoluble to water, the environmental fate and toxicity is related to the soluble (bioavailable) constituents of the substance. According to the T/D study results conducted for the target substance, the most soluble and critical components of this substance are lead and zinc which appear in the substance in sulphide and sulphate forms. Therefore, the read-across approach has been used for the CSA. The read-across data for toxicity to terrestrial organisms is not only focusing on the sulphate but also on the other bioavailable lead and zinc compounds. The read-across justification is presented in CSR annex I. The read-across data for terrestrial plants is based on test data using either soluble Pb or Zn salts or measured field data on Pb or Zn (dissolved) concentrations. The weight of evidence approach was used to make conclusions on the key values for CSA.

Based on the exposure considerations both lead and zinc emissions are relevant for the environmental exposure assessment and to evaluate the terrestrial toxicity of the target substance. For ES&RC, the PNECs were derived separately for both critical constituents of the target substance. The PNEC soil was derived by using the statistical extrapolation techniques taken into account all reliable toxicity data. See the CSR section 7.6 for further information on the PNEC derivation.

Toxicity of lead and its compounds

Based on the reliable (Klimisch score 2) read-across data for lead with NOEC or EC10 values for 12 different plant species, the toxicity varies from 57 mg/kg for Hordeum vulgare (oat) to 5225 mg/kg for (wheat). The lowest chronic toxicity (45-d EC10, Hordeum vulgare) value of 57 mg/kg (95% CL: 19.5-417 mg Pb/kg, no guideline) was selected as a key value for lead.

Toxicity of zinc and its compounds

Based on the reliable (Klimisch score 2) studies the NOEC and EC10 values to terrestrial plants vary between 32 mg/kg dw for Trifolium pratense and Vicia sativa to 5855 mg/kg dw for Triticum aestivum. The lowest chronic toxicity (32-d NOEC, Trifolium pretense) of 32 mg/kg (OECD 208) was selected as key value for zinc.

All toxicity data are expressed as spiked Zn concentration in soil and the studies were conducted by using either the nominal or measured concentrations. The studies from field investigations took into account the background correction of Zn concentrations in soil.

Conclusions for CSA:

Toxicity is evaluated by using the read-across data from the two critical and bioavailable constituents of the test substance (zinc and lead). As lead and zinc are both relevant for the environmental ES&RC, the toxicity data for both constituents are taken into account in the CSA, and the PNEC soil is derived for both critical constituents, and used as threshold values in the ES&RC.