Effect of silver nanoparticles on soil denitrification kinetics

The toxicity of silver nanoparticles to bacteria, while frequently demonstrated in laboratory settings, has not been well established within environmental media. This study investigates the effect of three different silver nanoparticles (35-60nm, uncoated and coated with 0.3% polyvinylpyrrolidone) at various concentrations (1, 10, or 100mg/L) on the microbial-facilitated soil denitrification process using native bacteria in a soil (Toccoa sandy loam) environment. The sorption of silver nanoparticles onto soil was observed through an isotherm study. It was found that silver nanoparticles exhibited much less toxicity to the denitrifying bacterial community than was expected. The toxicity was not correlated with either coatings or particle size; instead, only one type of larger silver nanoparticle (uncoated 50-nm silver particles) exhibited any toxicity, and only at a very high (100mg/L) concentration. Toxicity was linked, however, to the silver nanoparticle affinity for soil surfaces (K_d), as determined through the isotherm study. The particle with the lowest K_d value was also the only toxic silver nanoparticle. This study is novel in its observation of silver nanoparticle toxicity to a bacterial community in a soil environment. The results of this study highlight the importance of environmental media in nanoparticle studies and the need for nanoparticle partitioning studies in terrestrial environments.