Titanium dioxide in agricultural soils: Fate, transport and impact on microbial functioning
Tuesday, March 15, 2016
Marie Simonin is a postdoctoral associate in the Department of Biology
Abstract: Manufactured titanium dioxide nanoparticles (TiO2-NPs) are commonly used in diverse manmade products, like sunscreens, toothpastes, paints or papers. Along their life cycle from production to disposal, TiO2-NPs can be released in the environment, especially the soil through various pathways, such as agricultural amendments of biosolids. In vitro studies demonstrated TiO2-NPs toxicity on microorganisms but data are still scarce on the fate and ecotoxicity of these contaminants in soils. The objective of this work was to assess the influence of soil properties on (i) the physicochemical characteristics and the transport of TiO2-NPs, and (ii) on the TiO2-NPs toxicity towards soil microbial communities, especially of microbial functional groups involved on carbon and nitrogen cycles.
This work highlighted that soil properties influenced the aggregation and the surface charges of TiO2-NPs in soil solution. In the six agricultural soils studied, we observed a very low transport of these NPs in a soil column experiment. A study with soil microcosms enabled to show the low toxicity of TiO2-NPs for soil microbial communities, except in a silty-clay soil with a high organic matter content. In this soil, microbial activities and nitrifier abundances were strongly decreased and archaeal and bacterial community structure were altered. Furthermore, we observed negative effects on soil nitrification, even for very low TiO2-NPs concentrations (0.05 mg kg-1) which were explained by a high sensitivity of ammonia-oxidizing archaea (AOA) involved in this process. Additional studies in soil columns demonstrated that chronic contamination with TiO2-NPs caused more deleterious effects on nitrification than acute contamination. Altogether, these results indicate that NPs toxicity is modulated by soil properties such as pH and organic matter content and that key microbial processes like nitrification could be altered in presence of these metal oxide NPs.