Environmental Particles: Volume 1 PDF
Preview Environmental Particles: Volume 1
INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY ENVIRONMENTAL ANALYTICAL AND PHYSICAL CHEMISTRY SERIES Environmental Particles Volume 1 ENVIRONMENTAL ANALYTICAL AND PHYSICAL CHEMISTRY SERIES Environmental Particles Volume 1 Volume Editors Jacques Buffle Herman P. van Leeuwen Department of Inorganic, Laboratory for Physical Analytical, and Applied Chemistry and Colloid Chemistry University of Geneva Agricultural University Geneva, Switzerland Wageningen, Netherlands Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business First published 1992 by Lewis Publishers CRCPress Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 Reissued 2019 by CRC Press © 1992 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works This book contains information obtained from authentic and highly regarded sources. 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Disclaimer The publisher has made every effort to trace copyright holders and welcomes correspondence from those they have been unable to contact. ISBN 13: 978-0-367-25127-7 (hbk) ISBN 13: 978-0-429-28622-3 (ebk) Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Foreword This book reports critical reviews on sampling, characterization, and the role and behavior of particles in the environmental compartments: air, surface and ground waters, and sediments and soils. There is, presently, no clear definition of the word particle within the literature devoted to environmental science. It is often used with different meanings depending on the context and scientific discipline involved. For instance, biologists refer to bacteria or even phytoplankton as biogenic particles whereas, for chemists, the term particle is generally associated to nonliving entities. Most geologists and sedimentologists restrict the notion of particles to entities larger than 0.45 pm, whereas they may be much smaller for chemists and, even, subatomic for physicists. The situation is further confused since physical chemists and water treatment engineers often use the word colloid to refer to particles in the size range 1 to 100 pm, whereas biologists often use colloid for nonliving entities smaller than 0.45 pm. Finally, chemists often use the term macro- molecule for certain small colloids or particles (<0.1 pm). All of these examples clearly show that there is an obvious basic language difficulty for such a book which intends to present a multidisciplinary approach of particle characteristics. It is not the purpose of this book to try to establish the best definition of a particle, colloid, or macromolecule within the context of environmental sciences. The reader, however, should know that the word particle may be used mainly in this book with two different meanings: Particle as a general term will refer to any entity with a size larger than ~ 1 nm. This is, for instance, the meaning used in the title of this book. Entities with sizes smaller than 1 nm have a molecular weight of less than ~ 1000, i.e., they include all small molecules and ions normally involved in classical chemical reactions. This book is not focused on these compounds. They are of interest here, however, be- cause many of them may be toxic or vital and because their interactions with particles and the behavior of the latter largely control their cir- culation in the environmental compartments. Particle in the restricted sense will be used in principle to refer to living or nonliving entities larger than 0.45 pm. In this case, this word will be used to discriminate between three different size-classes of entities (Figure 1): solutes (<1 nm), colloids or macromolecules (1 nm < size < 0.45 pm), and particles (>0.45 pm). There is, obviously, no well-defined size limit between the various environmental types of particles, and those mentioned here are arbitrary. The basis for the limit at 1 nm is cited here. The limit at 0.45 pm is traditionally used by limnologists and oceanographers. Although it is mostly based on ex- perimental reasons, it has some rough meaning since (1) many organisms (except viruses) are larger, and (2) coagulation leading to sedimentation mostly occurs with larger particles (see Chapters 5 and 10). Figure 1. Nature and size domain of the most important particles of aquatic systems. In specific cases the words particles and colloids might be used differently in the following chapters. But, in all cases, their meaning should be obvious from the context and by taking into account the previously stated remarks. The term environmental particle (taken in its general sense) refers to par- ticles of natural origin found in environmental compartments. In the air, the presence of particles is primarily due to erosion, marine aerosol formation, and combustion processes (either natural or anthropogenic). The description of the means allowing the determination of origin, nature, and fate of atmo- spheric particles is the subject of Chapter 1. In aquatic systems (oceans, lakes, rivers, ground water, and sediment pore water), particles (Figure 1) are mainly produced by weathering processes (e.g., clays and metal oxides) and direct or indirect formation (e.g., calcium carbonate, silica, Fe and Mn oxyhy- droxydes, organic macromolecules, and cellular debris; see Chapters 6, 8, and 9) due to life processes. In these systems, therefore, living organisms play an important role in controlling the concentration and nature of particles. It is believed that they even indirectly control the behavior of nonbiogenic particles like clays. For instance, organic macromolecules may adsorb on their surface and strongly influence their reactivity towards adsorbable toxic or vital compounds, as well as their coagulation and sedimentation (see Chap- ter 6). Little is known about the size distribution of environmental particles because of difficulties in sampling, sample handling (see Chapters 5 and 6), insuffi- cient sensitivity and selectivity of analytical methods, and the lack of adequate theories which permit taking into rigorous account the physical and chemical heterogeneity of environmental samples. In all cases it must be realized that the size distributions of particles may be represented in different manners and give completely different pictures depending on whether particle mass, par- ticle number, or particle surface area is considered as the dependent variable (Figure 2). In most aquatic systems the mass is dominated by particles larger than a few |xm with smaller particles representing generally less than 10% (often <1%). If, however, the number of particles is considered for the same sample, particles smaller than 1 jxm are the dominant class by several orders of magnitude. Consequently it is important to choose the most pertinent representation of the data, depending on what is the studied process. For instance, a size distribution based on particle mass is preferable for studying the fluxes of sedimenting particles (dominated by large particles), whereas coagulation processes (affecting mostly small particles) are better related to a size distribution based on particle number. Similar considerations apply to the study of chemical reactivity of particles (Figure 3). In this case there is an additional difficulty since particles may react through the reactive groups located either on the external surface of the particle, for instance, with a crystallized iron oxide, or inside the particle itself, in the case of amorphous porous material, e.g., Fe oxyhydroxide, or of organic macromolecules, e.g., proteins and humic compounds. Depending on the degree of crystallinity of the particle, the surface area or the volume of the particles should be the dependent variable of interest for the size distribution, which may result in contradictory conclusions about the relative role of large and small particles. To make the choice a bit more difficult, large size particles more than small ones are often crystallized, which implies that the two size distributions should be considered simultaneously when studying the reactivity of particles. All these factors underline the urgent need of methods for specific chemical and physical characterization of environ- mental particles. Some of the analytical problems involved are discussed in Chapters 3, 4, 6, 7, 9, and 13. Development of such analytical methods Figure 2. Example of size distributions of important aquatic particles. a-Size distribution, based on particle mass, of the Rhine river particles in Netherlands (same data as ■ in Figure b-) b-Size distributions of various types of particles, based on particle number. Results based on fractionation by filtration; particle numbers and proportions of particle mass are values obtained for each filtration fractions. Figure 3. Size distribution of a well-characterized amorphous iron hydroxo phosphate formed in situ, by oxidation of Fe(ll), at the oxic-anoxic boundary of a eutrophic lake. Determination made by transmission electron microscopy. Particles have spherical shape, a-size distribution based on particle numbers; AN = pro- portion of particle number in each class, b-size distribution of the same sam- ple, based on particle volumes; AV = proportion of particle volume in each size class. cannot be done without simultaneously studying the properties of particles. The latter are discussed in Chapters 2, 4, 9, 10, 11, and 12. When compared to a homogeneous solution where classical chemical re- actions occur, the peculiar role of environmental particles results from the fact that not only do they react chemically with toxic and vital compounds, but they also have important biophysico-chemical properties which strongly
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