Feldspar minerals, hematite and quartz, calcination products of copper mining residues

Toxicity to microorganisms

Description of key information

As the solubility of the synthetic iron oxides is extremely low, effects on wastewater treatment plants are not likely to occur. In sewage treatment plants the insoluble iron oxides particles will be removed mechanically by sedimentation (Mann et al., 2000).  Additionally, Iron salts are used widely in sewage treatment plants (STPs) to remove nutrients such as phosphates by precipitation. They discharge at such plants at concentrations below typically 1 mg/l. The low solubility of iron salts and their widespread use as a precipitation agent in wastewater treatment means that iron is unlikely to be toxic to microorganisms. Thus, no effects on microbial activity were recorded in the studies performed by the registrant and in  publicationsat concentrations typically below 1 mg/l and according to a U.S. EPA survey effects are only seen at between 5 – 500 mg Fe/l; other studies report much higher concentrations in STPs. Therefore, no PNEC for microorganisms is derived (the Iron Platform, 2010). For LEAD: 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.