The inhibitory effects of (Ag⁺) and silver nanoparticles (Ag NP) 3-5 nm in diameter (stabilized with polyvinylpyrrolidone (PVP)) and 20 nm (stabilized with citrate) on nitrification rates of the model ammonia-oxidizing bacteria (AOB) Nitrosomonas europaea were investigated. Experimental solutions contained HEPES buffer and ammonia (NH₃) in the presence and absence...