The Biological Effect Of Nanocapsule Pesticide And Carbon Nanomaterials On Soil Microorganism

In this study, the biological effect of two nanomaterials on microorganism was analyzed by microcalorimetry, soil enzyme activity and molecular biology method and so on. The toxicity effect of nanomaterial on microorganism was investigated form the perspective of microbial energy metabolism, microbial abundance, microbial diversity, and microbial morphology and so on. This research provides a theoretical basis for the application of these two kinds of nanomaterials in the future.Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) were synthesized by chemical coprecipitation method with FeCl2·4H2O and FeCl3·6H2O as raw materials. The carboxymethyl-β-cyclodextrin-Fe3O4 magnetic nanoparticles (CM-β-CD-Fe3O4MNPs) were prepared by the dehydration-condensation reaction between Fe3O4 magnetic nanoparticles and carboxymethyl-β-cyclodextrin (CM-β-CD). A new nanopesticide, carboxymethyl-β-cyclodextrin-Fe3O4 magnetic nanoparticles-Diuron (CM-P-CD-Fe3O4MNPs-Diuron), was synthesized from an inclusion complex of CM-b-CD-Fe3O4MNPs as host and diuron as guest molecules. The transmission electron microscopy revealed it had an average diameter of 25 nm which is more or less the same as that of MNPs (average diameter-23 nm). The CM-β-CD grafting was confirmed by infrared spectroscopy. The maximum a loading of diuron by CM-β-CD-Fe3O3MNPs reaches 48.68 mg/g.In this work, the potential toxic effect of CM-β-CD-MNPs-Diuron and diuron on soil microbial was evaluated by microcalorimetry, urease enzyme and real-time quantitative PCR (qPCR). The thermokinetic parameters k and Qtotal were observed to decrease with increase in the loading of CM-β-CDMNPs-Diuron and diuron in soil. The IC50 of soil with the effect of CM-β-CDMNPs-Diuron is 107.07 mg/g (The inclusion quantity of diuron is 5.21 mg).This dose is much higher than the dose of diuron (283.5 μg/g) able to eliminate soil microbial activity. This result suggests that CM-β-CD-MNPs-Diuron has much lower toxicity to microorganism than diuron due to the more efficient and effective release of diuron from CM-P-CDMNPs-Diuron and certain degree of positive effect of Fe3O4 MNPs. The microcalorimetric analysis was in agreement with qPCR and the urease activity data.The biological effect of graphene on soil microorganism was investigated by microcalorimetry, urease enzyme and real-time qPCR. The relationship between thermal parameters and the concentration of graphene inferred that the graphene had some inhibition on soil microbial metabolism. When the soil exposed to graphene for 10 days, the changes of enzyme activity and the abundance of bacteria illustrated that the low concentration of graphene promoted the growth of some bacteria in the soil, which increased the overall bacterial metabolism.In this study, carbon dots (Cdots) with diameters of 5 nm and a large number of oxygen groups on the surface are produced using mixed-acid treatment. The biological effect of Cdots on soil microorganism was analyzed by microcalorimetry, soil enzymatic activities, and denaturing gradient gel electrophoresis (DGGE). The addition of Cdots causes a gradual increase of the maximum heat power (Ppeak) and the growth rate (k) at low concentration of Cdots (0.0-50.00 μg/g). But there is no significant effect of Cdots on the total heat output (Qtotal).The urease and fluorescein diacetate esterase activities demonstrate that introduction of Cdots to soil has almost no impact on the function of the soil microbial community. The DGGE results exhibit that the control and the Cdots-treated soils display similar patterns, indicating that Cdots have little effect on the microbial community structure.Gram-negative bacteria E. coli are applied as testing model to study the biological effect of Cdots on the cell growth by microcalorimetric, spectroscopic, and microscopic investigation. The introducing of Cdots caused a gradual increase of the maximum heat power (Ppeak) and the total heat produced (Qtotal) at low concentrations (0.0-5.00 mg/L). The results indicated that Cdots had a concentration-dependent effect on the growth of E. coli. For confirmation, the growth curves and colony-forming units at different concentration of Cdots were studied. The morphology of E. coli in the absence and presence of Cdots was determined by scanning electron microscopy (SEM). On the basis of these results, it can be deduced that Cdots have some antimicrobial and toxicant effect on the growth of E. coli.