Environmental behaviors of nanoparticles
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The increased production, use and disposal of nanoparticles (NPs) will ultimately lead to the environmental release of these materials, and thus understanding their environmental behaviors is necessary for an accurate environmental risk assessment. Phase distribution of NPs between aqueous and solid phases determines in which environmental compartment the NPs are most likely to reside; however, the system containing solid phase was merely been studied previously. Our results showed that the interaction between inorganic clay minerals and MWCNTs can be explained by van der Waal’s, electrostatic, and acid-base interactions and modeled by extended-DLVO theory, regardless of the mineral type (kaolinite or smectite). Diagenetically young organic matter, peat, sorbed MWCNTs only when cation was added, while released dissolved organic matter (DOM) that helped stabilize MWCNTs. However, diagenetically old organic matter in shale strongly sorbed MWCNTs. Meanwhile, smaller MWCNTs showed higher tendency to aggregate, but DOM impaired this tendency. Our results suggest that MWCNTs are not likely to be stably dispersed in hard water or seawater; instead, they preferentially accumulate in soil or sediment, unless there is DOM present. In addition, we at the first time reported that a bacteria community mineralized MWCNTs, i.e., degrade into CO2, which was confirmed by C14-labeling. This mineralization is likely performed by several bacteria species, including Burkholderia kururiensis, Delftia acidovorans, and Stenotrophomonas maltophilia, through co-metabolism that requires carbon source other than MWCNTs. The intermediates of low-molecular aromatic organic compounds were also detected. This indicates that microbes may modify the long-term fate of MWCNTs. The effect of nano-TiO2 to the growth of one major crop, wheat, was shown to be dependent on the type and dosage of nano-TiO2, the spiking method, the incubation time and the wheat genotype, which varied from negative, neutral to positive. The photosynthesis efficiency maintained a high level across the tested conditions, indicating the effect of nano-TiO2 may not last for long term. The uptake and translocation of nano-TiO2 to the root and shoot of wheat were also observed. Elevated level of peroxidase activity in root at 5 and 50 mg kg-1 soil dosage indicated the root is under oxidative stress.