Dose-response effects of silver nanoparticles and silver nitrate on microbial and enzyme activities in calcareous soils

The extensive use of silver nanoparticles (AgNPs) in consumer and medical products leads inevitably to release of such particles into environment and soil resources. This study was conducted to provide evidences for biological effects of AgNPs in two calcareous soils with different textures and salinity levels. Basal respiration (BR) and substrate-induced respiration (SIR), as indicators of soil microbial activity and biomass, respectively, were determined in the calcareous soils spiked with a dilution series of AgNPs and AgNO3. Urease and alkaline phosphatase activities were also measured in the spiked and control soils. Finally, dose-response approach was used to model the sensitivity of the soil biological properties to AgNPs and AgNO3 contamination. The results revealed that the effects of AgNPs and AgNO3 on the soil respiration and enzyme activities depended on Ag dose and soil type. For instance, soil respiration was not affected or even stimulated by low doses of AgNPs and AgNO3, but negatively affected by high doses (> 20 mg Ag kg− 1). Soil urease and phosphatase activities were generally inhibited in the presence of AgNPs and AgNO3, though in low Ag concentrations there was no inhibition or even stimulation. Generally, the ecological dose (ED) values of AgNPs were smaller than those of AgNO3, suggesting that AgNPs have more negative effects than AgNO3 on the soil microbial and enzyme activities, at the same level of Ag dose. The results also revealed that suppression of microbial and enzyme activities by AgNPs and Ag ions are greater in the soil with lower clay content and ionic strength.