Evidence for the inhibitory effects of silver nanoparticles on the activities of soil exoenzymes

Silver nanoparticles (AgNPs) are well known to have antimicrobial ability, but very little is known about the effect of AgNPs on soil exoenzyme activities, which reflect the potential of a soil to support biochemical processes. This study provides evidence of the inhibitory effects of AgNPs on the activities of soil exoenzymes. Six exoenzymes related to nutrient cycles (urease, acid phosphatase, arylsulfatase, β-glucosidase) and the overall microbial activity (dehydrogenase, fluorescein diacetate hydrolase) were tested in soils treated with AgNPs (1, 10, 100 and 1000 μg g(-1)) and silver ion (0.035, 0.175, 0.525, 1 and 1.5 μg g(-1)). AgNPs were capable of inhibiting the activities of all the exoenzymes tested in this study. Especially, the urease and dehydrogenase activities were significantly related to the presence of AgNPs. The effects of silver ions dissolved from the AgNPs were not significant, indicating the adverse effects caused by AgNPs themselves. This study suggested that AgNPs negatively affect soil exoenzyme activities, with the urease activity especially sensitive to AgNPs.