RESUMEN
Continuous increase in the usage of ZnO nanoparticles in commercial products has exacerbated the risk of release of these particles into the aquatic environment with possible harmful effects on the biota. In the current study, cytotoxic effects of two types of ZnO nanoparticles, having different initial effective diameters in filtered and sterilized lake water medium [487.5±2.55 nm for ZnO-1 NPs and 616.2±38.5 nm for ZnO-2 NPs] were evaluated towards a dominant freshwater algal isolate Scenedesmus obliquus in UV-C, visible and dark conditions at three exposure concentrations: 0.25, 0.5 and 1 mg/L. The toxic effects were found to be strongly dependent on the initial hydrodynamic particle size in the medium, the exposure concentrations and the irradiation conditions. The loss in viability, LDH release and ROS generation were significantly enhanced in the case of the smaller sized ZnO-1 NPs than in the case of ZnO-2 NPs under comparable test conditions. The toxicity of both types of ZnO NPs was considerably elevated under UV-C irradiation in comparison to that in dark and visible light conditions, the effects being more enhanced in case of ZnO-1 NPs. The size dependent dissolution of the ZnO NPs in the test medium and possible toxicity due to the released Zn(2+) ions was also noted. The surface adsorption of the nanoparticles was substantiated by scanning electron microscopy. The internalization/uptake of the NPs by the algal cells was confirmed by fluorescence microscopy, transmission electron microscopy, and elemental analyses.
Asunto(s)
Luz/efectos adversos , Nanopartículas/toxicidad , Scenedesmus/efectos de los fármacos , Scenedesmus/efectos de la radiación , Rayos Ultravioleta/efectos adversos , Contaminantes Químicos del Agua/toxicidad , Óxido de Zinc/toxicidad , Relación Dosis-Respuesta a Droga , Agua Dulce , Microscopía Electrónica de Rastreo , Microscopía Electrónica de Transmisión , Nanopartículas/química , Tamaño de la Partícula , Contaminantes Químicos del Agua/química , Óxido de Zinc/químicaRESUMEN
A new low cost adsorbents, pottery granules coated with cyst of Azotobacter and portland cement has been developed for aqueous arsenic removal. The developed granule is solid and porous structure forms a stable complex of Fe-Al-Si-O(2) allied with cyst biomass. Batch experiments were revealed that As removal was up to 96% using PGAC beads, whereas 65% by cyst biomass. Immobilization of cyst biomass to pottery granules through portland cement improved the stability of granules and adsorption capacity. Kinetics studies revealed that Langmuir isotherm was followed with a better correlation than the Freundlich isotherm and adsorption was first order diffusion controlled. Presence of Fe-Al-Si-O(2) and polysaccharide complex on the granule surface may be responsible for the adsorption of arsenic and preferentially binds to biomass containing composite than only biomass. Thus, this recently developed cost-effective novel biocomposite, PGAC granule can be used as household level to mitigate the arsenic problem.