Baalousha / Lead Characterization of Nanomaterials in Complex Environmental and Biological Media

1. Auflage 2015
ISBN: 978-0-08-099950-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, Band Volume 8, 320 Seiten

Reihe: Frontiers of Nanoscience

Characterization of Nanomaterials in Complex Environmental and Biological Media covers the novel properties of nanomaterials and their applications to consumer products and industrial processes. The book fills the growing gap in this challenging area, bringing together disparate strands in chemistry, physics, biology, and other relevant disciplines. It provides an overview on nanotechnology, nanomaterials, nano(eco)toxicology, and nanomaterial characterization, focusing on the characterization of a range of nanomaterial physicochemical properties of relevance to environmental and toxicological studies and their available analytical techniques. Readers will find a multidisciplinary approach that provides highly skilled scientists, engineers, and technicians with the tools they need to understand and interpret complicated sets of data obtained through sophisticated analytical techniques. - Addresses the requirements, challenges, and solutions for nanomaterial characterization in environmentally complex media - Focuses on technique limitations, appropriate data collection, data interpretation, and analysis - Aids in understanding and comparing nanomaterial characterization data reported in the literature using different analytical tools - Includes case studies of characterization relevant complex media to enhance understanding

Autoren/Hrsg.

Baalousha, Mohammed

Lead, Jamie

Leseproben

3. Sources, Entry and Fate of NMs in Aquatic Environments
Materials can occur naturally in the environment at the nanometre-size range and have existed for billions of years. Natural occurrences that derive from sources such as volcanic eruptions and forest fires can generate airborne NMs and nanosized components of natural organic macromolecule (NOM) in water and soil colloids. This has raised debate around the necessity for ecotoxicological testing for nanosized materials because organisms will have inevitably evolved over time to cope with these naturally occurring NMs. In stark contrast with natural NMs, however, engineered NMs have been designed to have specific properties to enable, for example, persistence and in turn are likely to pose different challenges to exposed organisms. Furthermore, for some materials, it is likely that the concentrations of NMs will exceed those found for these naturally occurring materials (e.g. silver). Aquatic environments act as sinks for anthropogenic discharges and receive NMs from divergent sources, including via wastewater treatment works (WWTWs) and surface runoff into rivers. This will be notable for NMs, such as CeO2 from fuels and TiO2 used in exterior paints, for ZnO and TiO2 entering directly into marine waters from the use of sunscreens, and also accidental releases from industrial plants producing these materials. Aquatic environments also receive NMs indirectly, for example, from soils where NMs are applied through treatments with sewage sludge, via leachate from landfill and/or via precipitation of materials released into the air. Importantly, no safety guidelines exist currently for NM release into aquatic environments. For metals, the UK and US governments have guidelines for water quality (UK Environmental Quality Standards and US EPA Aquatic Life Criteria)4,5 based on metal ions using the biotic ligand model (BLM). Recently the BLM has been applied to metal NMs but this approach is limited due to the high variability in the rate of dissolution for different sized NMs, which is also affected by the nature of the aqueous environment and capping agents present on the NMs. Furthermore, the BLM considers only the dissociating ions from the NMs and does not take into account possible NM-specific biological effects.6 When considering the ecotoxicity of NMs, we would emphasise that there is not sufficient information available currently to link any adverse effects to individuals or populations at concentrations likely to be found in most aquatic environments. Furthermore, information on adverse effects in individuals for any exposures that approach those with (predicted) environmental relevance are still very limited. 3.1. NM Sources and Entry into Aquatic Environments
WWTW discharges are expected to be one of the major sources of NMs into aquatic systems. WWTWs receive significant amounts of NMs from both domestic and industrial sources, and although some are expected to precipitate into the sludge (but may find their way back into aquatic systems via sludge applied to land as fertiliser), the remaining NMs in effluents will enter directly into both freshwater and marine environments. Data on measured levels of NMs in WWTWs influent and effluent are limited and releases of NMs predicted by modelling are highly variable depending on particle type and processes within the specific WWTWs. Measured releases of NMs in WWTW have been reported for C60 and C70 carbon NMs and some metal-based materials. For C60 and C70, carbon NM levels can reach the parts per billion (ppb) range.7 In a study using a model WWTW, 6% (by weight) of the CeO2-NMs supplied to the WWTWs were subsequently released in the effluent discharge and addition of associated stabilizing agents increased the amount of CeO2 passing through the WWTWs into the effluent stream.8 Predicted effluent concentrations for TiO2-NMs in WWTW effluents have been reported at between 0.7 and 16 µg L-1. The predicted no effect concentration (PNEC) for TiO2-NMs is < 1 µg L-1.9 One study has reported concentrations of titanium containing NMs (<0.7 µm) in WWTW effluents at concentrations in the range <5–15 µg L-1, exceeding the PNEC value.10 The fate and behaviour of silver NMs in WWTWs will depend on many variables including influent concentrations, NM coating, and NM transformation within the WWTW (e.g. sulphidation). Only a relatively small percentage of Ag-NMs pass through WWTWs into the effluent discharged as Ag-NMs, and most are transformed via sulphidation into Ag2S.11 The fate of Ag-NMs however is also size-dependent.12 Sulphidation of Ag-NMs reduces their solubility and toxicity, but the environmental impact of other transformations of Ag-NMs, such as oxidised silver sulphide, has not been established. A modelling approach has predicted effluent concentrations of uncoated Ag-NMs at less than 0.24 µg L-1 but higher concentrations for coated Ag-NMs.13 In a study in Germany, Ag-NMs concentrations in influents were measured at <1.5 µg L-1 and at <10 ng L-1 in effluents.14 Predicted environmental concentrations (PECs) for Ag-NMs indicate that at current levels of use they are unlikely to be an environmental problem for most aquatic environments, but their future use (and thus discharge into these environments) is set to increase significantly.11,13,15 Other direct sources of NMs into aquatic systems include via industry and hospital discharges, runoff from roads and applications such as agriculture (nanopesticides), exterior paintwork and sunscreens, and via use in soils remediation. There are little data available for the industrial production and release of NMs, and as a consequence studies modelling production levels of NMs have relied on extrapolated data.16 Hospitals use NMs extensively for health care, for example in imaging (gold and Q-dot NMs), antimicrobial wound dressings (silver and copper NMs) and for drug delivery and gene therapy (polymer/liposome-based NMs). Modelling approaches used to assess gold NM PECs, however, indicate at current usages; even at hot spot discharges from hospitals, they are unlikely to be an environmental problem.11 In one study the highest predicted water concentration of CeO2-NMs from road runoff into rivers was 0.02 ng L-1. It is not clear however how representative this is of runoff in waters in close proximity to roads, and after rain storm events.17 Measured concentrations of TiO2-NMs in runoff derived from newly painted (experimental) facades, have been measured up to 600 µg L-1.18 Studies to assess NM release from NM-containing products include the release of up to 650 µg L-1 of silver from socks (washed in 500 mL distilled water)15 and an average concentration of 11 µg L-1 of silver in washing machine effluent.19 For ZnO and TiO2 in sunscreens up to 25% of sunscreen is washed off on immersion20 and an estimated 250 tonnes of ZnO and TiO2-NMs are released into the marine environment from sunscreen use.21 Analysis of a lake's surface waters over a 12-month period found that residence times for TiO2-NMs from sunscreens were short, with an increase in TiO2 concentration only seen during the bathing season.22 Measured and predicted concentrations of selected NMs in selected effluent discharges and surface and marine waters are shown in Table 1. Soils can act as a repository for NMs, prior to their entry into aquatic environments, via sources including landfill leachate, atmospheric deposition, direct application of WWTW products to land as fertilisers or direct application of specific NMs for chemical remediation. The nature and fate of NMs in soil will depend on the physicochemical nature of that soil, and this will determine the amount of transfer of NMs into aquatic environments. Soils contain naturally occurring NMs in colloids, including a mixture of NOM, inorganic matter, bacteria and viruses. Interaction between NMs and these colloids affect rates of aggregation, transport, dissolution or deposition and in turn NM release into aquatic systems. In some instances, and as mentioned above, contaminated soils are treated directly with NMs, for example, the use of zero-valent iron to clean up heavy metals, pesticides, radionuclides and polychlorinated hydrocarbons32 and this is now a commercial enterprise using hundreds of kilograms of zero-valent iron NMs per km2 of contaminated land.3,31,33 Little is known, however, about the long term effects of these treatments.34 Table 1 Predicted Environmental Concentrations (PECs) and Modelled and measured Releases of NMs for Selected Sources Predicted Environmental Concentrations...