Low concentration effects and different outcome in repeated reproduction tests with silver nanoparticles, silver nitrate and Folsomia candida (Collembola)

Abstract

Background: Toxicity of silver nanoparticles (AgNP) has been studied frequently due to a rise in application in various products. Various studies on AgNP toxicity with terrestrial and aquatic organisms confirmed their negative effects. In our previous experiments, strong variability was observed in the reproduction of Collembola (Folsomia candida) in different repeats. To investigate the effects of silver on the reproduction of Folsomia candida, they were exposed in laboratory-controlled conditions to AgNP and silver nitrate (AgNO3) at a concentration of 30 mg/kg dry soil for 28 days and compared to controlled individuals not exposed to silver. We repeated reproduction tests on the toxicity of silver to Folsomia candida four times throughout one year (April, July, October and January) in order to explore the temporal variability of their outcome. Results: While adult survival was similar in all treatments and seasons, reproduction in the control increased from April to October. Significantly lower reproduction was found in January with only 385–424 juveniles per vessel, compared to 504–633 individuals in other months. Strong toxic effects of both silver treatments were observed in July, April and October. However, AgNP showed no toxic effects on the reproduction of F. candida in January. The relative toxicity of both substances varied between single experiments: AgNP were more toxic than AgNO3 in April and July, and less toxic in October and January. Conclusion: These findings indicate that the reproduction of F. candida in the control had a significant effect on the results of the toxicology experiments. Moreover, we demonstrated the reproductive toxicity of AgNP in soil at a much lower concentration than reported thus far. Therefore, to guarantee reliability and reproducibility, we recommend to disregard any test results where the reproduction rate of F. candida in the control is significantly different from the average in the respective laboratory, even if the validity criteria of the test are met.