Environmental and Low Temperature Geochemistry

Peter Crowley Ryan is Professor of Geology and Environmental Studies at Middlebury College where he teaches courses in environmental geochemistry, hydrology, sedimentary geology and interdisciplinary environmental science. He received a Ph.D. in geology at Dartmouth College, an M.S. in geology from the University of Montana and a B.A. in earth sciences from Dartmouth College. He has served as Director of the Program in Environmental Studies and as Chair of the Department of Geology at Middlebury College. His research interests fall into two main areas: (1) understanding the geological and mineralogical controls on trace element speciation, particularly the occurrence and mobility of arsenic and uranium in bedrock aquifers; and (2) the temporal evolution of marine terrace soils in the tropics, with emphasis on mechanisms and rates of mineralogical reactions, nutrient cycling and application of soil geochemical analysis to correlation and geological interpretation.

Acknowledgements, xii About the Companion Website, xiii 1 BACKGROUND AND BASIC CHEMICAL PRINCIPLES: ELEMENTS, IONS, BONDING, REACTIONS, 1 1.1 An overview of environmental geochemistry history, scope, questions, approaches, challenges for the future, 1 1.2 The naturally occurring elements origins and abundances, 2 1.3 Atoms and isotopes: a brief review, 6 1.4 Measuring concentrations, 8 1.4.1 Mass-based concentrations, 8 1.4.2 Molar concentrations, 9 1.4.3 Concentrations of gases, 10 1.4.4 Notes on precision and accuracy, significant figures and scientific notation, 10 1.5 Periodic table, 11 1.6 Ions, molecules, valence, bonding, chemical reactions, 14 1.6.1 Ionic bond strength, 14 1.6.2 Covalent bonds, 16 1.6.3 Electronegativity, 17 1.6.4 Metallic bonds, hydrogen bonds and van der Waals forces, 18 1.7 Acid base equilibria, pH, K values, 19 1.8 Fundamentals of redox chemistry and chemical reactions, 21 1.9 Chemical reactions, 23 1.10 Equilibrium, thermodynamics and driving forces for reactions: systems, gibbs energies, enthalpy and heat capacity, entropy, volume, 23 1.10.1 Systems, species, phases and components, 24 1.10.2 First law of thermodynamics, 26 1.10.3 Second law of thermodynamics, 27 1.10.4 Enthalpy, 27 1.10.5 Heat capacity, 29 1.10.6 Gibbs free energy, 30 1.10.7 Gibbs free energy and the equilibrium constant, 31 1.11 Kinetics and reaction rates: distance from equilibrium, activation energy, metastability, 33 1.11.1 Reaction rate, reaction order, 34 1.11.2 Temperature and the Arrhenius equation, 36 Review questions, 37 References, 37 2 SURFICIAL AND ENVIRONMENTAL MINERALOGY, 39 2.1 Introduction to minerals and unit cells, 40 2.2 Ion coordination, Pauling s rules and ionic substitution, 42 2.2.1 Coordination and radius ratio, 42 2.2.2 Bond-strength considerations, 45 2.2.3 Pauling s and Goldschmidt s rules of ionic solids, 45 2.3 Silicates, 48 2.3.1 Nesosilicates, 49 2.3.2 Inosilicates, 50 2.3.3 Phyllosilicates, 52 2.3.4 Tectosilicates, 58 2.4 Clay minerals (T O minerals, T O T minerals, interstratified clays), 58 2.4.1 Smectite, 59 2.4.2 Smectites with tetrahedrally derived layer charge, 60 2.4.3 Smectites with octahedrally derived layer charge, 60 2.4.4 Vermiculite, 62 2.4.5 Illite, 62 2.4.6 Chlorite and Berthierine, 63 2.4.7 Kaolin (kaolinite and halloysite), 63 2.4.8 Interstratified clay minerals, 64 2.4.9 Trace metals and metalloids in clay minerals, 64 2.5 Crystal chemistry of adsorption and cation exchange, 64 2.5.1 Cation exchange, 66 2.5.2 Double-layer complexes, 68 2.6 Low-temperature non-silicate minerals: carbonates, oxides and hydroxides, sulfides, sulfates, salts, 70 2.6.1 Carbonates, 70 2.6.2 Oxides and hydroxides, 71 2.6.3 Sulfides and sulfates, 72 2.6.4 Halide and nitrate salts, 74 2.7 Mineral growth and dissolution, 74 2.8 Biomineralization, 78 Review questions, 79 References, 80 3 ORGANIC COMPOUNDS IN THE ENVIRONMENT, 82 3.1 Introduction to organic chemistry: chains and rings, single, double, and triple bonds, functional groups, classes of organic compounds, organic nomenclature, 82 3.1.1 Definition of organic compounds, 82 3.1.2 Hybridization of carbon atoms in organic compounds, 83 3.1.3 Alkanes, 84 3.1.4 Alkenes, 86 3.1.5 Functional groups, 86 3.1.6 Aromatic hydrocarbons and related compounds, 88 3.1.7 Nitrogen, phosphorus and sulfur in organic compounds, 92 3.1.8 Pharmaceutical compounds, 93 3.2 Natural organic compounds at the earth surface, 94 3.2.1 Fossil fuels, 95 3.3 Fate and transport of organic pollutants, controls on bioavailability, behavior of DNAPLs and LNAPLs, biodegradation, remediation schemes, 96 3.3.1 Solid liquid gas phase considerations, 96 3.3.2 Solubility considerations, 97 3.3.3 Interactions of organic compounds and organisms, 98 3.3.4 Adsorption of organic compounds, 99 3.3.5 Non-aqueous phase liquids (NAPLs) in the environment, 103 3.3.6 Biodegradation, 104 3.3.7 Remediation, 105 3.4 Summary, 106 Questions, 106 References, 106 4 AQUEOUS SYSTEMS CONTROLS ON WATER CHEMISTRY, 108 4.1 Introduction to the geochemistry of natural waters, 108 4.1.1 Geochemistry and the hydrologic cycle, 108 4.2 The structure of water geometry, polarity and consequences, 113 4.3 Dissolved versus particulate: examples of solutions and suspensions, 114 4.3.1 Dissolved vs. particulate vs. colloidal, 115 4.4 Speciation: simple ions, polyatomic ions and aqueous complexes, 116 4.5 Controls on the solubility of inorganic elements and ions, 117 4.5.1 The ratio of ionic charge: ionic radius and its effect on solubility, 119 4.5.2 Reduction oxidation reactions, 120 4.5.3 Half-cell reactions, 120 4.5.4 Redox reactions in the environment, 122 4.5.5 pH and acid base consideration, 123 4.5.6 Ligands and elemental mobility, 124 4.6 Ion activities, ionic strength, TDS, 125 4.6.1 Ion activity product, 126 4.6.2 Ionic strength, 126 4.6.3 Total dissolved solids, 126 4.7 Solubility products, saturation, 127 4.8 Co-precipitation, 128 4.9 Behavior of selected elements in aqueous systems, 129 4.9.1 Examples of heavy metals and metalloids, 129 4.9.2 Eh pH diagrams, 132 4.9.3 Silicon in solutions, 136 4.10 Effect of adsorption and ion exchange on water chemistry, 137 4.10.1 Ionic potential, hydration radius and adsorption, 138 4.10.2 Law of mass action and adsorption, 138 4.10.3 Adsorption edges, 140 4.10.4 Adsorption isotherms, 142 4.11 Other graphical representations of aqueous systems: piper and stiff diagrams, 143 4.12 Summary, 146 Questions, 147 References, 147 5 CARBONATE GEOCHEMISTRY AND THE CARBON CYCLE, 149 5.1 Carbonate geochemistry: inorganic carbon in the atmosphere and hydrosphere, 149 5.1.1 Atmospheric CO2, carbonate species and the pH of rain, 150 5.1.2 Speciation in the carbonate system as a function of pH, 151 5.1.3 Alkalinity, 152 5.1.4 Carbonate solubility and saturation, 155 5.1.5 The effect of CO2 partial pressure on stability of carbonate minerals, 157 5.1.6 The effect of mineral composition on stability of carbonate minerals, 157 5.2 The carbon cycle, 158 5.2.1 Oxidation states of carbon, 158 5.2.2 Global-scale reservoirs and fluxes of carbon, 159 5.2.3 Fixation of carbon into the crust, 161 5.2.4 Rates of flux to and from the crust, 164 5.2.5 The ocean reservoir, 166 5.2.6 Fixation of C into oceans, 166 5.2.7 Long-term viability of oceans as C sink, 168 5.2.8 The atmospheric reservoir, 171 5.2.9 Sequestration, 174 Questions, 175 References, 176 6 BIOGEOCHEMICAL CYCLES N, P, S, 177 6.1 The nitrogen cycle, 180 6.1.1 Nitrogen valence, nitrogen species, 181 6.1.2 Processes operating within the nitrogen cycle, 182 6.1.3 Global scale reservoirs and fluxes of nitrogen, 184 6.1.4 Human perturbation of the nitrogen cycle and resulting environmental impacts, 186 6.2 The phosphorus cycle, 190 6.2.1 P cycling in soils, 191 6.2.2 The global phosphorus cycle, 193 6.2.3 Phosphorus and eutrophication, 194 6.3 Comparison of N and P, 195 6.4 The sulfur cycle, 196 6.4.1 Sulfur valence, sulfur species, 196 6.4.2 The global S cycle, 197 6.4.3 The marine S cycle, 198 6.4.4 Soils and biota, 200 6.4.5 Atmosphere, 200 6.4.6 River flux, 201 6.5 Integrating the C, N, P and S cycles, 202 Questions, 203 References, 203 7 THE GLOBAL ATMOSPHERE: COMPOSITION, EVOLUTION AND ANTHROPOGENIC CHANGE, 206 7.1 Atmospheric structure, circulation and composition, 206 7.1.1 Structure and layering of the atmosphere, 207 7.1.2 Geological record of atmospheric composition, 208 7.1.3 Climate proxies, 209 7.1.4 Orbital control on C, 210 7.1.5 Composition of the current atmosphere, 213 7.1.6 Air circulation, 214 7.2 Evaporation, distillation, CO2 dissolution and the composition of natural precipitation, 218 7.3 The electromagnetic spectrum, greenhouse gases and climate, 219 7.3.1 Electromagnetic spectrum, 219 7.3.2 Re-radiation from earth surface, 219 7.3.3 Greenhouse effect and heat trapping, 222 7.4 Greenhouse gases: structures, sources, sinks and effects on climate, 223 7.4.1 Molecular structures and vibrations of greenhouse gases, 223 7.4.2 Greenhouse gases, radiative forcing, GWPs, 224 7.4.3 Global warming, 227 Questions, 228 References, 228 8 URBAN AND REGIONAL AIR POLLUTION, 230 8.1 Oxygen and its impact on atmospheric chemistry, 231 8.2 Free radicals, 232 8.3 Sulfur dioxide, 234 8.4 Nitrogen oxides, 237 8.5 Carbon monoxide, 238 8.6 Particulate matter, 240 8.7 Lead (Pb), 242 8.8 Hydrocarbons and air quality: tropospheric ozone and photochemical smog, 242 8.9 Stratospheric ozone chemistry, 245 8.10 Sulfur and nitrogen gases and acid deposition, 249 8.11 Trace elements in atmospheric deposition: organochlorine pesticides, mercury and other trace elements, 252 8.11.1 Pesticides in air, 252 8.11.2 Hg in air, 253 8.11.3 As, Cd and Ni, 254 Questions, 255 References, 256 9 CHEMICAL WEATHERING AND SOILS, 258 9.1 Primary minerals, mineral instability, chemical weathering mechanisms and reactions, soil-forming factors, and products of chemical weathering, 258 9.1.1 Goldich stability sequence, 259 9.1.2 Weathering rates, 260 9.1.3 Chemical weathering, 261 9.1.4 Consequences of chemical weathering: dissolved species and secondary minerals, 264 9.1.5 Geochemical quantification of elemental mobility in soil, 265 9.1.6 Quantifying chemical weathering: CIA, 267 9.1.7 Soil profile, 268 9.1.8 Soil-forming factors, 268 9.1.9 Soil classification soil orders and geochemical controls, 273 9.2 Secondary minerals, controls on their formation, and mineral stability diagrams, 275 9.2.1 Factors controlling soil mineralogy, 275 9.2.2 Mineral stability diagrams, 276 9.3 Soils and the geochemistry of paleoclimate analysis, 281 9.4 Effects of acid deposition on soils and aquatic ecosystems, 282 9.4.1 Increased solubility of Al in acidic soil solution, 283 9.4.2 Displacement of adsorbed nutrient cations, 284 9.4.3 Leaching of base cations enhanced by increased NO3 and SO4, 285 9.4.4 Decrease of soil buffering capacity and base saturation, 286 9.4.5 Acid deposition and heavy metals, 287 9.5 Soils and plant nutrients, 287 9.6 Saline and sodic soils, 289 9.7 Toxic metals and metalloids, 290 9.8 Organic soil pollutants and remediation (fuels, insecticides, solvents), 294 Questions, 295 References, 296 10 STABLE ISOTOPE GEOCHEMISTRY, 299 10.1 Stable isotopes mass differences and the concept of fractionation, 299 10.2 Delta ( ) notation, 302 10.3 Fractionation: vibrational frequencies, temperature dependence, 304 10.3.1 Stable isotopes and chemical bond strength, 305 10.3.2 Temperature-dependent stable-isotope fractionation, 305 10.3.3 Equilibrium and non-equilibrium isotope fractionation, 307 10.4 18O and D, 309 10.4.1 Paleotemperature analysis using oxygen and hydrogen isotopes, 314 10.4.2 Oxygen and hydrogen isotopes as tracers in the hydrologic cycle, 314 10.4.3 Application of oxygen and hydrogen isotopes to paleosol climate records, 316 10.5 15N, 316 10.6 13C, 318 10.6.1 Carbon isotope analysis of paleoenvironment, 320 10.6.2 Carbon isotopes in hydrology and chemical weathering, 321 10.7 34S, 321 10.7.1 Fraction of sulfur isotopes, 322 10.8 Non-traditional stable isotopes, 324 10.8.1 65/63Cu, 325 10.8.2 56/54Fe, 326 10.8.3 202/198Hg, 326 10.8.4 26Mg and 44/42Ca, 328 10.8.5 37/35Cl, 330 10.9 Summary, 330 Questions, 331 References, 331 11 RADIOACTIVE AND RADIOGENIC ISOTOPE GEOCHEMISTRY, 335 11.1 Radioactive decay, 335 11.1.1 Decay mechanisms and products, 336 11.1.2 Half-lives, decay rates and decay constants, 337 11.2 Radionuclides as tracers in environmental geochemistry, 341 11.2.1 206Pb/207Pb, 341 11.2.2 87Sr/86Sr, 342 11.3 Radionuclides as environmental contaminants, 342 11.3.1 Controls on U, Th and their decay products, 342 11.3.2 Refined uranium ores and associated nuclear wastes, 346 11.3.3 Geological disposal of high-level radioactive wastes, 349 11.4 Geochronology, 350 11.4.1 14C, cosmogenic radionuclides and earth-surface dating techniques, 350 11.4.2 Common radioactive decay methods of dating sediments and minerals, 359 11.4.3 234U/238U and 234U disequilibrium, 364 Questions, 367 References, 367 APPENDIX I CASE STUDY ON THE RELATIONSHIP OF VOLATILE ORGANIC COMPOUNDS (VOCs), MICROBIAL ACTIVITY, REDOX REACTIONS, REMEDIATION AND ARSENIC MOBILITY IN GROUNDWATER, 371 I.1 Site information, contaminant delineation, 371 I.2 Remediation efforts, 372 I.3 Sources of PCE and As, 374 I.4 Mobilization of arsenic, 374 References, 377 APPENDIX II INSTRUMENTAL ANALYSIS, 378 II.1 Analysis of minerals and crystal chemistry, 378 II.1.1 Electron microscopy (SEM, TEM and many other acronyms), 378 II.1.2 X-ray diffraction, 379 II.1.3 FTIR, 382 II.1.4 Elements in solution by ICP-AES, ICP-MS, AAS, 384 II.1.5 XRF, 385 II.1.6 X-ray absorption spectroscopy (XAS) techniques (EXAFS, XANES), 385 II.1.7 Isotopic analysis: mass spectrometry, 387 II.1.8 Chromatography, 389 References, 389 APPENDIX III TABLE OF THERMODYNAMIC DATA OF SELECTED SPECIES AT 1 ATM AND 25 C, 390 Index, 394