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

Toxicity to soil macroorganisms except arthropods

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 of the target substance.

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.

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; lead and zinc. For further information on the PNEC derivation see CSR section 7.6.

Toxicity of lead and its compounds

Fifteen individual NOEC or EC10 values for 4 different species have been selected for WoE approach ranging from 130 mg/kg for Dendrobaena rubida (earthworm) to 4718 mg/kg for Folsomia candida. Similar toxicity tests are reported in different source documents (i.e. using the same organism, endpoint, soil and test conditions). For these cases, a geometric mean value is calculated. Two geometric mean values are calculated for tests with invertebrates. A geometric mean value is calculated based on 2 results for reproduction of Eisenia fetida in an OECD artificial soil (Spurgeon and Hopkin, 1995: NOECr = 608 mg/kg; Spurgeon et al., 1994: NOECr = 1822 mg/kg). The geometric mean is 1053 mg/kg in the total risk approach.

The second geometric mean value is calculated based on 2 results for reproduction of Eisenia fetida in a silt loam soil (Davies et al., 2002: NOECr = 400 mg/kg; Davies et al., 2003b: NOECr = 625 mg/kg). The geometric mean is 500 mg Pb/kg.

Two tests with Folsomia candida are also performed in the same OECD soil at pH 6.0 (Sandifer and Hopkin, 1996: NOECr = 2000 mg/kg/EC10r = 1678 mg/kg; Sandifer and Hopkin, 1997: NOECr = 400 mg/kg). However, the temperature was not the same in both tests: 20°C (Sandifer and Hopkin, 1996) versus 15°C (Sandifer and Hopkin, 1997). In the second test, toxicity of Pb to F. candida reproduction was also measured at 20°C. This resulted in a NOECr = 2000 mg/kg which is consistent with the first study. As temperature has a clear effect on the toxicity of Pb to F. candida reproduction, no geometric mean value has been calculated.

All together 13 NOEC/EC10 values were selected for the HC5 calculations to determine the PNEC soil for the exposure assessment and risk characterization of the target substance to estimate the RC of the lead emissions via air deposits. See the CSR section 7.6 for further information on the PNEC derivation.

Based on the WoE on soil macro-organisms the lowest toxicity (16-wk NOEC, Dendrobaena rubida Sav.) on natural soils for lead is 130 mg/kg soil dw at pH 4.5.

Toxicity of zinc and its compounds

The reliable (Klimisch score 2) studies for zinc compounds with NOEC or EC10 values on soil macro-organisms are available covering 6 different worm species and the results vary from 35.7 mg Zn/kg (Lock and Janssen, 2001c) for Enchytraeus albidus to 1634 mg Zn/kg dw for Lumbricus terrestris (Spurgeon et al., 2000). All toxicity data are expressed as spiked Zn concentration in soil based on either the nominal or measured concentrations, or background corrected soil Zn concentrations, when the results are from natural soils.

Based on the WoE approach on the results to soil macro-organisms, the lowest toxicity (42-d EC10, Eisenia fetida) for zinc is 35.7 mg/kg (OECD 220).

Based on the WoE approach on the reliable (Klimisch score 2) studies on reproduction of arthropods with NOEC/EC10 values representing 2 different species, the toxicity is between 14.6 and 1000 mg Zn/kg dw (both for Folsomia candida; Lock and Janssen, 2001c and Lock et al., 2003). The lowest chronic toxicity (28-d EC10, Folsomia candida (reproduction juveniles)) for zinc (14.6 mg/kg) was selected as a key value.

The PNEC soil was derived by using the statistical extrapolation techniques taken into account all reliable toxicity data. All toxicity data is expressed as spiked Zn concentration in soil and the studies have been conducted by using on either the nominal or measured concentrations. In the field studies the background correction for Zn concentrations in soil has been used. The PNEC soil for exposure assessment and risk characterization of the target substance was derived to estimate the RC of the zinc emissions via air deposits. See the CSR section 7.6 for further information on the PNEC derivation.

Conclusions for CSA:

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