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EC number: 936-276-2 | CAS number: -
Toxicity to microorganisms
Administrative data
Link to relevant study record(s)
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. Based on exposure considerations the target substance is not connected to the biological treatment, though the PNEC STP has no onsite relevancy in the ES&RC.
Key value for chemical safety assessment
- EC10 or NOEC for microorganisms:
- 0.1 mg/L
Additional information
The environmental hazard assessment was conducted based on the most critical constituents of the substance. This substance is an 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. Conclusion for this endpoint is based on read-across data from zinc and lead compounds.
Toxicity of lead and its compounds
Short-term toxicity data were extracted from literature for bacteria (heterotrophs and nitrifiers) and different protozoan species. 2 different no-effect levels for lead, between 1.06 and 2.92 mg/L (depending on the exposure time), were compiled for heterotrophic bacteria. For nitrifiers, 2 different no-effect concentrations, between 2.79 and 9.59 mg/L, were observed. 14 different short-term toxicity data were selected for protozoan species/communities. No-effect concentrations for protozoan communities varied between 1.0 and 7.0 mg Pb/L, while LC50 values for protozoan varied between <1.5 and >250.0 mg/L.
Toxicity of zinc and its compounds
A nitrification inhibition test with Zn sulfate on activated sludge originating from a municipal wastewater treatment plant was performed leading to a NOEC of 100 µg Zn/L.
Several data were available for this endpoint. Formerly (ECB 2008), and in the REACH-registrations of a number of zinc substances of November 2010, a PNEC of 52 µg/L for STP was derived, based on the lowest EC50 of 5.2 mg Zn/L observed in a sludge respiration inhibition test (Dutka et al. 1983). According to the guidance (ECHA 7.8.17.1) preference should be given to nitrification inhibition because respiration inhibition is a less sensitive endpoint. A study conducted by Juliastuti et al. (2003) reported a NOEC of 0.1 mg Zn/L in an ISO 9509 nitrification inhibition test. Applying the rules for PNEC setting (ECHA R.10, table R.10.6) this result yields a PNEC STP of 100 µg Zn/L (AF of 1).
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, zinc has the the lowest key value (0.1 mg/L) for toxicity to microorganisms. Based on exposure considerations the target substance is not connected to the biological treatment, though the PNEC STP has no onsite relevancy in the ES&RC.
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