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Ecotoxicological information

Toxicity to soil microorganisms

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The most sensitive effects data is an EC10 of 0.30 mg/kg Ag for effects on nitrogen transformation in a 28 day OECD 216 test. The physico-chemical conditions of the soil were pH 7.3, Organic Carbon 1.3 % and clay <11 % (Naddy 2011).

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Additional information

Long-term toxicity data for soil micro-organisms are available for a range of natural soils.

Chronic toxicity of silver in artificial soil (pH 7.3, organic carbon 1.3%, clay 11%) to microorganisms was also tested in a 28-day nitrogen transformation test following OECD guideline 216 by Naddy (2011). A NOEC of 0.13 mg Ag/kg, a LOEC of 0.45 mg Ag/kg and an IC10 of 0.30 mg Ag/kg are reported in the study.

The toxicity of silver to soil microorganisms was also investigated using a soil nitrogen (N) transformation test (OECD guideline 216, 2000) for six study soils (Langdon et al. 2013). Two test endpoints were reported from the study: total NO3 production and potential nitrification rate (PNR). The 28-day EC10 values for NO3 production ranged from 0.65 (Bordeaux) to 371 mg Ag/kg (Millicent) and for PNR were between 1.2 (Bordeaux) and 488 mg Ag/kg (Millicent) in unleached soils. The toxicity of silver to the soil nitrification process was primarily controlled by soil pH and OC.

The effects of silver on soil microorganisms were investigated in a 28 day ammonium oxidation test (Schlich et al. 2013b). After 28 days, the NOEC was 0.56 mg/kg dry soil and the EC10 was 1.4 mg/kg dry soil.

A number of other studies on the effects of silver on terrestrial microorganisms are included as supporting studies in the dossier. However, they are considered less reliable than the studies reported by Naddy (2011), Langdon et al. (2013) and Schlich et al. (2013b) as they do not follow a standard methodology.