Silver

Toxicity to soil microorganisms

Description of key information

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).

Additional information

Chronic toxicity of silver in artificial soil (pH 7.3, organic carbon 1.3%, clay 11%) to microorganisms was 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.

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

The toxicity of silver to soil microorganisms was 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 to soil microrganisms using a soil nitrogen (N) transformation test (OECD guideline 216, 2000) was also assessed for three study soils by Smolders andWillaert (2017). Two test endpoints were reported: the potential nitrification rate (PNR) and substrate induced nitrification (SIN).Soil samples from three different arable soils (Rots, Poelkapelle and Lufa 2.2) were collected from the plough layer (0-20 cm). The soils were selected to have a pH between 4.3 and 7.3, %OC between 1.1 and 6.8% and CEC between 9.7 and 33.9 cmol_c/kg. Based on 0-14 day PNR, the EC10 values (measured total silver) ranged from 3.8 to 8.1mg Ag/kg, and corresponding EC50 values ranged from 36 to 66 mg Ag/kg. Based on 28 day SIN,the EC10 values (measured total silver) ranged from 30 to 45mg Ag/kg, and corresponding EC50 values ranged from 100 to 134 mg Ag/kg.

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), Schlich et al. (2013b), and Smolders and Willaert (2017), as they do not follow a standard methodology.