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

Toxicity to aquatic plants other than algae

Description of key information

According to transformation/dissolution study (OECD guidance 29) conducted for the substance, the most critical constituents leachable to water from this UVCB substance are lead and zinc compounds. Therefore, the chemical safety assessment focuses on the properties of constituents and the key values for CSA are selected based on the read-across data on the most bioavailable compounds of Pb and Zn.

Key value for chemical safety assessment

EC10 or NOEC for freshwater plants:

29.5 µg/L

Additional information

The environmental hazard assessment was conducted based on the most critical constituents of the substance. This substance is an inorganic UVCB substance and can be described as a moist solid powder which is insoluble to water. Therefore, the transformation/dissolution study (OECD guidance 29) was conducted for the substance and the results of this study were used for the chemical safety assessment.

According to the chemical composition analysis, the main phases of the substance are lead sulphate and zinc sulphide. The product consists primarily of sulphur (ca. 35 %), lead (ca. 25 %) and zinc (ca. 17 %) together with minor trace elements such as silver, silicon, aluminium, calcium and iron.

According to T/D study results, the most soluble and critical components of this substance are lead and zinc. Therefore, the studies for this endpoint have been selected as a read-across data for the critical constituents. The read-across justification is presented in CSR annex I. All read-across data for ecotoxicology are based on test data using either soluble Pb or Zn salts or measured (dissolved) Pb or Zn concentrations. The weight of evidence approach was used to make conclusions on the key value for CSA.

Toxicity of lead and its compounds

Data consists from 6 IC10 values for higher plants with values between 29.5 µg Pb/L (Lemna minor; endpoint: root length) and 643.2 µg Pb/L (Lemna minor; endpoint: root length).

The freshwater lowest chronic toxicity (7-d IC10, Lemna minor (root length)) value: 29.5 µg/L (95% CI 18.9-45.9 µg/L, OECD 221)

Toxicity of zinc and its compounds

Chronic NOECs are available for one multicellular algae species (0.06 mg Zn/l) and for 4 higher aquatic plant species (all NOEC results >650µg Zn/l). The EU risk assessment on zinc (ECB 2008) used one chronic NOEC on Cladophora glomerata in the PNEC database. Additional information on long term experiments on 4 higher aquatic plant species was used as supportive evidence, demonstrating the low sensitivity of this taxonomic group.

The freshwater lowest chronic toxicity (3-d NOEC, Cladophora glomerata (growth rate)) value: 60 µg/L (no guideline)

Conclusions for CSA:

Toxicity of the test substance is evaluated by using WoE read-across data from the two critical components of the the test substance (zinc and lead). From the toxicity data, lead has the lowest key value for toxicity to aquatic plants other than algae. Therefore, the toxicity value from lead was used as key value for CSA. However, as lead and zinc are both relevant for environmental ES&RC, key values from both constituents were used for PNEC-derivation and taken into account in the exposure assessment (CSR sections 9&10).