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

Toxicity to other above-ground organisms

Description of key information

According to transformation/dissolution study (OECD guidance 29) conducted for the target substance, the most biovailable constituent of the target substance is lead. It is also nonessential and the most hazardous constituent in relation to the secondary poisoning. Therefore, the chemical safety assessment focuses on the toxicity of lead and the key value for CSA is selected from lead toxicity studies on mammals and used for the PNEC oral derivation.

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for mammals:

64 mg/kg food

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. The read-across justification is presented in CSR annex I.

Lead is considered to be the most critical constituent in relation to the bioaccumulation and secondary poisoning for exposure of man via environment. This conclusion is based on the bioaccumulation potential of lead and its nonessential and toxic nature.Zinc is an essential element that is regulated throughout the food chain and does not bioaccumulate/biomagnify.

On the other hand, lead iscarcinogenic, reproduction toxic and causes repeated dose toxicity. It is also the main component and the only readily soluble constituent of the target substance based on the T/D study. In soil, lead has a strong binding capacity to organic matter especially to humic surface soils, and it has bioaccumulation potential to animals and plants. Therefore, the secondary poisoning is focusing on the properties of lead. The exposure assessment and risk characterisation for man via environment focuses on the lead emissions via inhalation and via food consumption. The following read-across data on lead was used to derive the PNEC oral for mammals. For further information on PNEC derivation, see CSR section 7.6.

Toxicity of lead and its compounds

The lowest NOEC for mammals refers to a full chronic study for mammals (Morris et al. 1938), which resulted in a NOEC value of 64 mg Pb/kg ww. Sub-chronic and chronic studies for 3 different mammal species were collected from literature, i.e. for Rattus sp. (different strains), Rattus norvegicus and for mice. For mammal oral toxicity, the values vary between 64 to >12800 mg/kg ww. The lowest value of 64 mg Pb/kg ww (423-d NOEC, Osborn-Mendel rat) was used to derive the PNEC, which was observed in several experiments. According to the guidance, the PNEC oral was calculated from the lowest NOEC oral using an assessment factor.

An assessment factor of 6 has been selected on the lowest toxicity data. Considering a background concentration of 1.3 mg Pb/kg in the food, the PNEC oral can be calculated as: PNEC oral= (NOEC +Cb) /AF = (64+1.3) /6 =10.9 mg/kg food (mammal). This value is further used for risk characterisation purposes.