• Measuring available concentrations of Nanomaterials in contaminated soils

      Pouran, Hamid; Lofts, Steve; McGrath, Steve; Zhang, Hao (2015-10-01)
      Nanoscience is facing a turning point, after years of research it has entered commercialization stage and a number of nanotechnology products are expected to enter the market. Apart from environmental impacts of emerging products there are a number of nanomaterials that are already widely used in different industries namely, ZnO, Ag and TiO2 nanoparticles. These nanomaterials could enter into the environment through different paths including the production stage, waste management and recycling or accidents. It is known that these nanomaterial have adverse environmental impacts. However, a major challenge that still exists is to better understand their fate and behaviour in the environment, which is not possible without access to proper and reliable sampling techniques. Here we present application of a modified DGT device known as Nano-DGT, which in combination with standard DGT devices could provide a reliable approach to measure available concentrations of zinc oxide, silver and titanium dioxide nanoparticles in the environment. In this research, as part of TINE (Transatlantic Initiative for Nanotechnology and the Environment) collaborations, soil samples were spiked with different concentrations of ZnO, Ag and TiO2 nanoparticles and their respective ionic forms were studied. For each soil sample a Nano- DGT, with 1000 MWCO (molecular weight cut off) dialysis membrane in the front of the diffusive gel layer, and a standard DGT device (DGT Total) were deployed in triplicates. The deployment times were approximately 18 hours. As it has been difficult to obtain accurate diffusion coefficients of those nanomaterials due to their variable nature, average mass accumulated (M) by DGT was used as a reliable measure to reveal differences between available metals in their nanoparticle and ionic forms. Among three different metals used in these studies, ZnO NP and ionic zinc seem to be the most available ones. Average concentrations of accumulated metal (M) are significantly lower for TiO2 NP and its ionic form followed by Ag NP and Ag+. This could be attributed to retention of these metallic spices by active surfaces in the soils samples (e.g. organic matter), which make them less available for DGT measurements. Interestingly the samples, even those that were spiked by ionic metals only, showed considerably higher accumulated metals for the DGT devices compared to Nano-DGT. This indicates notable fraction of freely available ions formed high molecular weight complexes in the soil.
    • Measuring available concentrations of ZnO NPs in soils using Nano-DGT

      Pouran, Hamid (2015-10-01)
      Zinc oxide nanoparticles, ZnO NPs, are used in a range of commercially available products including sun tan lotions and semiconductors. Increasing number of ZnO NPs incorporated products will likely raise concentration of this nanomaterial in the environment. Available information suggests that ZnO NPs can easily enter soil and water resources. ZnO NPs have adverse effects on different components of the environment in particular because of their toxicological impacts. Zinc oxide nanoparticles are one of the most toxic nanomaterials and could inhibit the root growth of plants and embryonic development of some of marine species. To better understand fate and behaviour of these nanoparticles in the environment and their potential pathways, determining in-situ concentration of these nanomaterials is essential. We have recently used Nano-DGT in combination with standard DGT devices to determine available concentrations of zinc oxide nanoparticle and its ionic species in soil samples spiked with a range of concentrations from 100 mg/kg to 2200 mg/kg of ZnO NPs and Zn2+. The samples were aged approximately for 80 Days after spiking. For each soil sample a Nano-DGT and a standard DGT device were deployed for approximately 20 hours (in triplicates). The results showed that for the samples spiked with ZnO NPs, available concentrations of zinc species measured by DGT devices were notably higher than Nano-DGT devices. Nevertheless considerably high concentrations of available zinc were also measured by Nano-DGTs, which could partly be attributed to dissolution of ZnO NPs and released Zn2+ because of the soil pH (5.5). In the soil samples spiked with ionic zinc the available concentrations measured by Nano-DGT and DGT devices were approximately 1.5X higher for the spiked samples with 100, 225, 500 and 1100 mg/kg ZnO NP. This ratio was more than twice for the soil samples spiked with 2200 mg/kg ionic zinc.