Toxicity of surface functionalized iron oxide nanoparticles toward pure suspension culture and soil microcosm

Abstract

Surface functionalized iron oxide nanoparticles are increasingly being used in environmental and medical applications, raising concerns on their fate and environmental impact. In this work, Fe3O4 nanoparticles prepared by a chemical co-precipitation method were functionalized with citric acid, polyethylene glycol of molecular weights 6000 and 8000, and methacrylic acid. Resazurin reduction-based nanoparticles toxicity assessment was performed with suspended microbial culture (50–250 mg L−1 NPs) as well as in soil microcosm (250–1250 mg kg−1). Resazurin reduction by freely suspended E. coli cultures in presence of uncoated, citric acid- and PEG-coated nanoparticles was either comparable or higher than that of the nanoparticle free control. However, the toxicity of methacrylic acid coated nanoparticles was evident as resazurin reduction was largely inhibited. Residual resazurin in test sets containing nanoparticle spiked seven days aged sterile soil were 20% to 82% that of freshly spiked control, suggesting significant attenuation of toxicity in soil media. The results obtained from this work may provide a better understanding of the impact of engineered iron-oxide nanoparticles in the soil ecosystem.