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

Endpoint summary

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 organisms 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.

The target substance is considered as having adsorption potential to soil and organic matter. Based on the CSA, the adsorption potential to soil is stronger for lead than for zinc. The soil adsorption coefficients for these critical constituents of the target substance are6400 PbL/kg (log 3.81) and158.5 ZnL/kg (log 2.2), respectively. Lead is also considered to be more critical constituent in relation to the bioaccumulation and secondary poisoning for exposure of man via environment than zinc. This conclusion is based on the bioaccumulation potential of lead and its nonessential and toxic nature. Zinc asan essential element serves as micronutrient and is used for redox-processes, to stabilize molecules through electrostatic interactions, as components of various enzymes, and for regulation of osmotic pressure in the terrestrial compartment (Bruins et al. 2000). On the other hand, lead is nonessential element which iscarcinogenic, reproduction toxic and causes repeated dose toxicity. It is also the main component and the only readily soluble constituent of the target substance (T/D study; OECD guidance 29). In soil, lead has a strong binding capacity to organic matter especially to humic surface soils. However, Friedland et al. (1992) found that lead complexed with dissolved organic matter may migrate from the surface layer to mineral soil, thus raising the concern of lead contaminating the groundwater.

However, since lead and zinc are both bioavailable from the target substance and the emissions via air deposits from the manufacture and the end-use are relevant for both constituents; the toxicity to terrestrial compartment is evaluated based on the toxicities of both lead and zinc. The exposure assessment and risk characterisation is assessed for both lead and zinc emissions and therefore also the PNEC soil has been derived for both constituents. However, the secondary poisoning and toxicity to birds is focusing on the properties of lead. PNEC oral is based on the mammalian toxicity studies on lead and its bioavailable compounds.

The soil characteristics such as organic matter and clay content, soil pH, cation exchange capacity (CEC) and soil moisture content affects on the terrestrial toxicity in natural soils. In addition, the aging and weathering have effects on the toxicity in terrestrial compartment. The read-across data used for lead and zinc contains both test data on artificially contaminated soils and data on contaminated soil samples from the field studies. Therefore, the PNEC soil was derived by using the statistical extrapolation techniques.

Read-across data on lead compounds

The ecotoxicological data are based on the data in the VRAL for Pb and Pb substances (data derived from original papers on the subject, published in international journals and research projects) and a literature update for new published relevant data since 2001. Identical reliability and relevancy criteria used as in the VRAL (LDAI, 2008).

When EC₁₀values are not reported in the original study, but data are available allowing derivation of a concentration-effect relationship, the EC₁₀is calculated using a logistic (sigmoidal) dose-response curve by minimising the unweighted squared residuals sum. A minimum of control and 3 test concentrations are required for derivation of a dose-response curve. If no reliable EC₁₀can be derived because e.g. no significant dose-response curve can be fitted or the EC₁₀is outside the concentration range tested, and a “real”, bounded NOEC value can be derived, this NOEC value will be used instead of the EC₁₀for PNEC derivation. No unbounded NOEC or LOEC values are used for derivation of the PNEC.

Read-across data on zinc compounds

In the EU risk assessment on zinc, an extensive analysis was made of the available terrestrial toxicity data, available at that time (ECB 2008). The data were carefully scrutinised for quality and relevancy by the Rapporteur and member states. In the present exercise, all data that were considered useful for deriving the PNEC soil in the risk assessment are used. In addition, an update of the terrestrial toxicity data that became available after the closure of the EU RA, has been made. Based on this update, the PNEC derivation for Zn in soils has been revised. This PNEC derivation is now based on the data and bioavailability models presented in the Risk Assessment Report (RAR) for Zn under the existing substances regulation, the comments of the SCHER on this RAR and new reliable data not yet included in the RAR.

All toxicity data judged reliable and relevant in the RAR for Zn are included (171 NOEC or EC10 values). On March 2 2010, an additional literature search was performed covering the scientific literature since 2000 for new reliable toxicity data for Zn on terrestrial organisms (plants, invertebrates and micro-organisms). This new data search resulted in 43 new NOEC or EC10 values. For further explanations of the PNEC derivation, see the CSR section 7.6.