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

Toxicity to aquatic algae and cyanobacteria

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

EC50 for freshwater algae:

21.7 µg/L

EC10 or NOEC for marine water algae:

52.9 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

Freshwater:

For algae, 7 individual reliable freshwater acute toxicity data points for one species were available for hazard assessment. The acute toxicity values (48h-LC50) for Pseudokirchneriella subcapitata varied between of 21.7 µg dissolved Pb/L (at pH 7.5 and hardness of 24.2 mg/L) and 322.9 µg dissolved Pb/L (at pH 7.3 and hardness of 174.4 mg/L). 2 different chronic high quality no-effect levels for dissolved lead for freshwater algae were between 34.1µg Pb/L and 93.0 µg Pb/L (Pseudokirchneriella subcapitata).

The freshwater lowest chronic toxicity (48-h EC50, Pseudokirchneriella subcapitata (growth rate)) value: 21.7 µg/L (95 % CI 20.1-23.5 µg/L, OECD 201)

Marine:

High quality no-effect levels for dissolved lead for marine algae plants were between 52.9 µg Pb/L (Skeletonema costatum; endpoint: yield) and 1231.8 µg Pb/L (Dunaliella tertiolecta; endpoint: growth rate).

The marine lowest toxicity (96-h EC10, Skeletonema costatum (average specific growth rate)) value: 52.9 µg/l (95% CI 42.3 - 66.3 µg, ASTM E1218 2006)

Toxicity of zinc and its compounds

Freshwater

Chronic freshwater data is available for 2 species. Tests are of high quality and relevancy and they were done according to standard protocols or equivalent. The lowest IC50 value to freshwater algae was 0.136 mg Zn/l (Selenastrum capricornutum; single value) (neutral/high pH). The lowest NOEC to freshwater algae was 0.019 mg Zn/l (Pseudokircherniella subcapitata = Selenastrum capricornutum) calculated from as geometric mean fom 27 results).

Acute freshwater toxicity tests are of high quality and relevancy and they were performed according to standard protocol. Information is available from 1 species (Pseudokircherniella subcapitata) which is the most sensitive organism for zinc in both acute and chronic toxicity.

The freshwater lowest toxicity (72-h LC50, Pseudokirchnerella subcapitata (growth rate)) value: 0.136mg/L (OECD 201)

Marine

Data consist from chronic seawater tests with high quality and relevancy and they were done according to standard protocols or equivalent. Data is available from 12 different species, results range between 7.2 µg/l (Ceramium tenuicore) and 1090 µg/l (Macrocystis pyrifera).

The marine lowest toxicity (EC10 7-d, Ceramium tenuicore, (length) value: 7.2 µg/L (according to author the test will become an international standard within ISO).

Conclusions for CSA:

Toxicity of the test substance is evaluated by using WoE read-across data from the two critical components of the test substance (zinc and lead). From the toxicity data, lead has the lowest key values for toxicity to freshwater and marine aquatic algae and cyanobacteria. Therefore, the toxicity values from lead were used as key values 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).