Identification,Distribution And Environmental Impacts Of Nanoparticles In Typical Environmental Samples

With the development of nanotechnology,more and more nanomaterials are applied to our daily consumer products.These nanoparticles?NPs?continuously and inevitably enter into the environment through our daily activities.With small size and unique physicochemical properties,NPs have high ecotoxicity and cytotoxicity,and can serve as carriers for other pollutants,posing potential environmental risks.The identification,characterization and quantitative analysis of NPs in the environment are significantly important to investigate and explore the occurrence and fate of NPs in the environment and their subsequent environmental risks.Therefore,in this study,metals and metal-containing NPs in three typical environment samples,that road dust,sewage sludge and sediments,which are all important sinks of NPs in the environment,are thoroughly investigated by various analytical techniques,such as aerosolization,single particle-inductively coupled plasma mass spectrometry?SP-ICP-MS?,metal speciation analysis and electron microscopy techniques.In addition,an extraction method of NPs in sediments has also been developed.Shanghai,a megacity adjacent to the Yangtze River Estuary,is selected as the research area for this study,and the road dusts and sewage sludges from Shanghai and sediments from the Yangtze River Estuary are very representative.Based on SP-ICP-MS,the extraction and separation of NPs in sediments via ultrasonic dispersion is optimized.In this study,gold and silver NPs,with known particle sizes and concentrations,were spiked into the sediment sample as reference materials.The particle concentrations and size distributions of Ti-,Zn-,Au-,Ag-NPs in sediments were simultaneously determined,considering the effects of sedimentation and filtration,settling time,ultrasonic power,ultrasonic time,sediment-to-water ratio and temperature on the extraction efficiency of the inherent NPs?Ti-,Zn-NPs?and the spiked NPs?Ag,Au-NPs?.It is found that the sedimentation with a settling time of 6 h is the best for the separation of NPs and large particles,and the optimal ultrasonic power,ultrasonic time,sediment-to-water ratio and temperature are 285 W,20 min,0.4 mg/m L,and 15-25°C,respectively.Taking the sediments from the Yangtze River Estuary for example,the particle concentrations and size distributions of Ti-,Zn-containing NPs in the sediments were analyzed base on the extraction method above.Moreover,the speciation and bioavailability of metals in sediments were investigated by the BCR sequencial extraction method and DTPA/CaCl₂ single reagent extraction methods.The results show that the salinity is an important influence factor for the migration and distribution of Ti-containing NPs.Moreover,Ti-containing NPs in sediments are likely to originate from the non-bioavailable fraction of Ti,indicating that the residual fraction,which is considered“environmentally safe”in the traditional environmental risk assessment of metals,is probably not safe.Zn-containing NPs and dissolved Zn in sediments are all derived from the bioavailable fraction of Zn,and their migration and distribution may be the joint effect of various environmental factors,such as salinity and TOC.The particle sizes,particle concentrations in number and in volume of Ti-containing NPs and the dissolved Ti in sediments from the Yangtze River Estuary are in the range of25.4-34.1 nm,2.16×10⁷-9.8×10⁷ parts/mg,3.29×10¹¹-2.04×10¹² nm³/mg and 7.38-43.19?g/g,respectively,with the averages of 30.9 nm,5.57×10⁷ parts/mg,9.07×10¹¹nm³/mg and 22.20?g/g,respectively.The particle sizes,particle concentrations in number and in volume of Zn-containing NPs and the dissolved Zn in sediments are in the range of 18.9-34.4 nm,1.86×10⁶-1.52×10⁷ parts/mg,2.05×10¹⁰-1.12×10¹¹ nm³/mg and 0.9-14.05?g/g,respectively,with the averages of 24.6 nm,6.71×10⁶ parts/mg,4.79×10¹⁰ nm³/mg and 6.26?g/g,respectively.In addition,Cd,Cu,Zn and Pb in the sediments of the Yangtze River Estuary are on different levels of metal pollution,among which the Cd pollution is the most serious.In addition,Mn,Zn,and Cd are more likely to exist as carbonate-bound metals in the sediments,and when the environmental pH changes,these metals are easily dissolved and released.While Cu and Pb are more likely to be organic matter-bound metals,which are easily absorbed and utilized by plants.Based on SP-ICP-MS,Ti-,Fe-,and Zn-containing NPs,with the concentrations of 10⁶-10¹¹ parts/g,were determined in the easily bioavailable chemical fractions of metals in sediments.These NPs have been ignored in these common evaluation methods of the metal bioavailiability in sediments.Taking the sewage sludge from Shanghai wastewater treatment plants for example,26 sewage sludge samples were investigated for the first time using a sequential extraction method coupled with single particle inductively coupled plasma mass spectrometry?SP-ICP-MS?in order to quantify the abundance of metal-containing NPs in different metal chemical fractions.Moreover,the transmission electron microscopy was applied to specifically identify the nanophase of particles in sewage sludge.In general,most sludges observed show high concentrations of Cr,Cu,Cd,Ni,Zn and Pb,exceeding the maximum permitted values in the national application standard of acid soil in China.NPs in these sludges contribute little to the volume/mass,but account for about half of the total particle number.Based on electron microscopy techniques,various NPs were further identified,including Ti-,Fe-,Zn-,Sn-,Pb-containing NPs.All NPs,ignored by the traditional metal risk evaluation method,are observed at a concentration of 10⁷-10¹¹ parts/g within the bioavailable fraction of metals.These results indicate the underestimate or mis-estimation in evaluating the environmental risks of metals based on traditional sequential extraction methods.NPs resulting from urban road dust resuspension are an understudied class of pollutants in urban environments with strong potential for health hazards.Taking the road dusts from Shanghai for example,based on the novel aerosolization system,66road dust samples were characterized using an array of techniques including ICP-MS,aerosol size distribution measurements and electron microscopy techniques.Results show that metals are generally enriched in aerosolized samples relative to the bulk dust.Elevated concentrations of metals are found mostly in downtown areas with intense traffic.Fe-,Pb-,Zn-,Ba-containing NPs with various sources were identified using electron microscopy techniques,and dangerous Pb sulfide and sulfate NPs are sometimes associated with Sn;which originate from an e-waste plant.Size distributions of most aerosolized samples presente a peak in the nano scale?<100 nm?.We estimate that 3.2±0.7?g/mg of Shanghai road dust may become resuspended in the form of PM2.5.Aerosolization,as done in this study,seems to be a very useful approach to study NPs in dust.