Silver docosanoate

Toxicity to soil macroorganisms except arthropods

Description of key information

The most sensitive effects data is an EC10 of 0.22 mg/kg Ag for reproduction in Eisenia fetida from a 70 day exposure. The physico-chemical conditions of the soil were pH 8, organic carbon 1.8% and clay 12% (Langdon et al. 2013).

Additional information

Long-term toxicity data for soil macro-organisms are available for four species (Eisenia andrei [Oligochaetea], Eisenia fetida [Oligochaetea], Folsomia candida [insect] and Porcellionides pruinosus [Crustacea]. Toxicity tests were undertaken in soils with a range of physico-chemical conditions.

Eisenia andrei data are available from the earthworm reproduction test according to OECD guideline 222 (Schlich et al. 2012). Two tests with silver nitrate were conducted in RefeSol 01A (pH 5.67, Organic Carbon 0.93 and clay 5%). EC10s for reproduction of 21.03 mg/kg and 15.39 mg/kg (nominal) were calculated based on the results reported in the study.

Key long-term data for E. fetida are available from reliable studies (Langdon et al. 2013, Pillard 2011a, Shoults-Wilson 2011a, 2011b) and from one unpublished report by Ortiz and Lahive (EU Nanofate Project). The earthworm toxicity study by Langdon et al. 2013 was conducted according to the OECD guideline 222 (Earthworm Reproduction Test) in soils (leached and unleached) and was undertaken in a range of soils indicative of natural variability in soil conditions across the EU (pH 4.6 – 8.0, organic carbon 0.9 – 6.9, and clay 2.5 – 60%). Reproduction (number of juveniles) was found to be the most sensitive endpoint in the study. The EC10 values based on this endpoint ranged from 0.2 (Port Kenny soil) to 67 (Inman Valley soil) mg Ag/kg in the unleached treatment. The EC10 values for survival were in the range of 5.3 (Kingaroy soil) – 141 (Balaklava soil) mg Ag/kg the unleached treatment. The toxicity of Ag to soil invertebrates appeared to be controlled primarily by organic carbon. Earthworm growth was also observed in the study. However, due to the small number of EC10 and EC50 values that could be calculated from the data, no analysis was conducted to determine the effect of soil properties on this toxicity endpoint.

Pillard 2011a exposed E. fetida to silver nitrate in artificial OECD soil (pH 7.2, Organic Carbon 4.3 and clay 15%) according to the OECD guideline 222. The study reports a 56-d EC10 of 15.05 mg/kg for earthworm reproduction and a 28-d EC10 of 194.5 mg/kg for survival.

Two studies with the earthworm Eisenia fetida exposed to a range of concentrations of AgNO3 in artificial soil (pH 6.23, Organic Matter 7.65%, clay 14.17%) following OECD guideline 222 were performed (Shoults-Wilson et al. 2011a and 2011b). Both studies report a comparative exposure with ionic silver, resulting in a reproduction NOEC of 8.38 mg/kg calculated from the data presented in the studies

Ortiz and Lahive (EU Nanofate Project) exposed the earthworm E. fetida to AgNO3 in four different soil types in a test according to OECD guideline 222. Reproduction was found to be the most sensitive endpoint in the study and 56-d EC10 values of 57.3 mg/kg and 13.22 mg/kg were calculated from Lufa 2.2 and Woburn soils, respectively. 28-d EC10 values of 190.78 mg/kg and 86.73 mg/kg in Lufa 2.2 and Woburn soil, respectively, were calculated from the survival data.