Nanotechnology and the Environment - Chapter 5

5 Analyses of Nanoparticles in the Environment Marilyn Hoyt AMEC Earth & Environmental CONTENTS 5.1 Analytical Methods .....................................................................................101 5.1.1 Nanoparticle Imaging: Size, Shape, and Chemical Composition ....101 5.1.1.1 Electron Microscopy ..........................................................101 5.1.1.2 Scanning Probe Microscopy (SPM) ...................................106 5.1.2 Compositional Analysis ...................................................................108 5.1.2.1 Single Particle Mass Spectrometer.....................................108 5.1.2.2 Particle-Induced X-Ray Emission (PIXE) .........................109 5.1.3 Surface Area: Product Characterization and Air Monitoring .........109 5.1.3.1 The Brunauer Emmett Teller (BET) Method .....................109 5.1.3.2 Epiphaniometer ..................................................................109 5.1.3.3 Aerosol Diffusion Charger ................................................. 110 5.1.4 Size Distribution .............................................................................. 110 5.1.4.1 Electrostatic Classifiers ...................................................... 110 5.1.4.2 Real-Time Inertial Impactor: Cascade Impactors .............. 110 5.1.4.3 Electrical Low Pressure Impactor (ELPI).......................... 111 5.1.4.4 Dynamic Light Scattering (DLS) ....................................... 111 5.2 Workplace Air Monitoring ..........................................................................112 5.2.1 Condensation Particle Counter (CPC) ............................................. 113 5.2.2 Surface Area: Total Exposure .......................................................... 113 5.3 Sampling and Analysis of Waters and Soils for Nanoparticles .................. 114 5.4 Nanotechnology Measurement Research and Future Directions ...............115 5.4.1 United States ....................................................................................115 5.4.1.1 NIOSH ................................................................................115 5.4.1.2 U.S. Government-Sponsored Research .............................. 117 5.4.1.3 National Institute of Standards and Technology (NIST) ... 117 5.4.2 European Union ............................................................................... 118 5.4.3 Asia-Pacific ...................................................................................... 118 5.5 Summary .......................................................................................... 119 References .............................................................................................................. 119 99 © 2009 by Taylor & Francis Group, LLC 100 Nanotechnology and the Environment The rapid explosion of production and use of engineered nanoparticles has outpaced the scientific community’s ability to monitor their presence in the environment. Without measurement data, it is not possible to fully evaluate whether the promises of nanoparticles are accompanied by significant ecological or human health risks. Numerous national and international agencies and research groups have recognized this gap and put in place research programs to address it. However, the technical requirements for the detection and characterization of nanoparticles in complex environmental systems push the limits of current sampling techniques and instru-mentation. In most cases, multiple complementary measurements are likely neces-sary to detect and understand the importance of nanoparticles in air, water, or soil because physical properties as well as chemical composition determine activity and environmental impact or risk. Environmental analyses of nanoparticles are not com-mon offerings at commercial environmental laboratories at this time, and they are not likely to become so in the near future. In the manufacturing industry, the development and production of nanoparti-cle materials for commercial applications are supported by an array of analytical methods. While numerous methods can successfully characterize the chemistry and physical properties of nanoparticles in relatively pure states and under defined condi-tions, the applicability of these methods to nanoparticles in environmental settings may be more limited. Once nanoparticles enter the environment, they may cluster to form larger particles, interact with particles from natural sources, or change chemi-cally. Conventional environmental analysis methods as developed and standardized by the U.S. Environmental Protection Agency (EPA) are bulk analyses; they can detect the primary chemical constituents of nanoparticle materials but little else of use for characterizing risk from them. In addition, the target nanoparticles may only be a minor component of an environmental sample and fall below the detec-tion limits of standard EPA chemical analysis methods. Collection and separation of nanoparticles from larger environmental particles, when even possible, are difficult, and their analysis is in most cases time-consuming and costly. No standard methods with prescribed quality control requirements for environmental nanoparticle analy-ses exist, and only limited traceable standards have been developed. Aside from the technical challenges to nanoparticle measurement in environ-mental media, the lack of specific regulations limits the incentive for commercial environmental laboratories to put in place the costly instrumentation and the high degreeofexpertisethatwillberequiredtooffernanoparticleanalysestogovernment, private industry, or public groups. While there is some concern for possible envi-ronmental risks from nanoparticles, manufacturers, users, and site owners currently are not required to address these concerns with actual environmental measurement data. As a result, most technical advances and data that do exist for environmen-tal analyses have come from academic laboratories and governmental or privately funded research laboratories. The applicability of regulatory statutes as discussed in Chapter 4 of this book continues to be debated. The Toxic Substances Control Act (TSCA), the Clean Water and Clean Air Acts (CWA, CAA), the Resource Conserva-tion and Recovery Act (RCRA), and the Federal Insecticide, Fungicide, and Roden-ticide Act (FIFRA) drove method development for numerous industrial chemicals in the environment. Regulatory requirements applicable to nanomaterials likewise © 2009 by Taylor & Francis Group, LLC Analyses of Nanoparticles in the Environment 101 would be expected to drive the development and standardization of environmental nanoparticle analytical methods for wider application, as well as to foster competi-tion in an emerging market for laboratory services. Instrumentation and staffing costs will, however, remain a barrier to entry into the f ield for most commercial laboratories currently offering environmental services. 5.1 ANALYTICAL METHODS The production of nanoparticle materials typically requires control of the chemical composition, size, shape, and surface characteristics of the material. Many of the analytical techniques applied for the analysis of nanoparticles during development and production also are critical to laboratory studies of fate and transport and expo-sure effects to ensure that the material being tested is fully understood. These meth-ods also may be components of analyses to detect nanoparticles after their release into the environment, dispersion in air or water, or uptake into organisms [1]. This chapter discusses highlights of the most widely used techniques, provid-ing the basic science of the analyses and describing the type of information that can be expected and reported for possible environmental applications. These tech-niques, as listed in Table 5.1, represent what must be considered initial approaches of researchers to address environmental issues; it is likely that over time, other current techniques or newly developed instrumentation will also prove useful. Representa-tive citations are provided where methods have proven successful for analyses of nanoparticles present in air, water, or soils. However, it should be noted that most environmental analyses reported to date for nanoparticles have focused on natural species such as colloids in water or on combustion-related emissions. Engineered nanoparticles have been characterized in laboratory studies and in indoor air moni-toring programs, but only limited studies designed to detect their releases into or fate in ambient air, surface or ground waters, or soils or waste have been reported [2]. More in-depth discussions of the theoretical basis for each measurement tech-nique, specifics for instrument design, detection options, and data examples can be found in a review article [3] that discusses more than 30 measurement techniques in detail, presenting the theory and advantages and limitations to each. Labora-tory analyses, real-time methods, and portable instrumentation for particulate characterization from mobile source emissions are reviewed in a literature survey for the California Air Research Board (ARB) [4]. Many of the methods discussed and equipment illustrated are also potentially applicable to measurement of nanopar-ticles from other sources in the environment. A recent U.S. EPA symposium on nanoparticles in the environment discussed the challenges involved, and also pre-sented highlights of applicable measurement methods [5]. 5.1.1 NANOPARTICLE IMAGING: SIZE, SHAPE, AND CHEMICAL COMPOSITION 5.1.1.1 Electron Microscopy Electron microscopy is comparable to light microscopy, except that a beam of elec-trons rather than light is used to form images. Electron beams have a much shorter wavelength than light and, as a result, they can provide the resolution required to © 2009 by Taylor & Francis Group, LLC TABLE 5.1 Methods for Environmental Analyses of Nanoparticles Technique Parameters Measured Resolution/Sensitivity Limitations/Advantages Environmental Applications Nanoparticle Imaging Electron microscopy (SEM, TEM, ESEM) Scanning probe microscopy (STM,AFM) Particle size, shape, texture, crystalline vs. amorphous structure, elemental composition, bonding Particle size, morphology 1 nm SEM, <0.1 nm TEM 0.5 nm Particle-by-particle analysis, time-consuming. Sample preparation, high vacuum for SEM, TEM may alter particles. ESEM allows imaging in water or other liquid media Particle-by-particle analysis. Analysis at ambient pressure, particles may be in solution Ambient air studies [11], nanoparticle characterization for laboratory studies of fate, toxicity [7–10] Ambient air studies, natural colloids [15–17, 20, 21] Compositional Analysis Single-particle mass spectrometry Particle-induced x-ray (PIXE) BET Epiphaniometer Aerosol diffusion charger Chemical composition, organic and inorganic species Elemental mapping of nanofilms or collected nanoparticles Average surface area on a mass basis Active surface area Aerosol surface area 3 nm particle 1 micron Surface Area 2000 m2/g 10–20 nm particles, 0.003 m2/cm3 10 to 100 nm in diameter Continuous analysis of particles in air stream Requires radioactive source. Laboratory-based instrument; requires relatively pure bulk sample of chemically homogenous material. Requires radioactive lead source Fast response Atmospheric studies, vehicular emissions [23, 24] Air pollution studies [28] Characterization for laboratory studies of fate, toxicity [29] Ambient air studies [30] Ambient air [31] © 2009 by Taylor & Francis Group, LLC Electrostatic classifier (DMA, NDMA, DMPS, SMPS) Cascade impactor, MOUDI Electrical impactor (ELPI) Light scattering (DLS, PLS, QELS) Particle distribution based on assumed spherical shape Particle distribution based on aerodynamic diameter Particle distribution based on aerodynamic diameter Particle size based on hydrodynamic diameter Size Distribution 5 nm <30 nm diameter <10 nm (MOUDI) 7 nm, >90 nanoparticles/ cm3 air; 5 ng/m3 0.7 nm Monitors on real-time basis; size will not necessarily be same as from imaging technique Time-integrated average distributions; particles collected may be analyzed subsequently by microscopy Real-time particle counts In situ measurements possible Releases during nanopowder use [33] Ambient air studies, vehicle emissions [35] Indoor air, ambient air studies, vehicular emissions [36, 37] Characterization of nanomaterials prior to laboratory studies [38–40] Particle Concentration/Surface Area in Air Condensation particle counter Electrical aerosol detector Particle concentration in air 3 nm stream Aerosol diameter concentration, 10 nm calculated from a number concentration multiplied by average diameter No information on particle size, shape composition. Hand-held units available, real-time data. Real-time data generation, field- portable instrumentation Indoor air monitoring, worker exposure studies [43] Ambient air studies [45] Particles in Aqueous Samples Field-Flow Fractionation Particle separation by size 1 nm diameter; 1–5000 ng/L for elemental composition Must be combined with subsequent analysis to assess size, (e.g., DLS). Can combine with ICPMS, ESEM. Natural colloids, iron oxide/ hydroxide colloids [49, 50] © 2009 by Taylor & Francis Group, LLC ... - tailieumienphi.vn