Table Of ContentSOIL AND ENVIRONMENTAL
CHEMISTRY
SOIL AND
ENVIRONMENTAL
CHEMISTRY
SECOND EDITION
William Bleam
UW-Madison,DepartmentofSoilScience
Madison,WI,UnitedStates
AMSTERDAM (cid:129) BOSTON (cid:129) HEIDELBERG (cid:129) LONDON
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v
Second Edition Preface
I made numerous major changes in this The biochemistry community often uses
the second edition of Soil and Environmental a pH 7 standard state that differs from
Chemistry. One that will be immediately the pH 0 standard state used by the pure
apparent was a decision to adopt insofar chemistrycommunity.Assuch,IUPACdoes
as possible the notation and nomenclature not endorse a special notation for reduction
recommended by the International Union of half-reactions under biochemical standard
Pure and Applied Chemistry IUPAC. This was stateconditions.InthesecondeditionIhave
motivated,inpart,toclarifytherootsofsoil adoptedthenotationusedbyAtkinsandde
chemistry, geochemistry, and environmental Paula (2005) in Physical Chemistry for the Life
chemistry in pure chemistry and, in part, Sciences.
to make this particular field of applied Finally,thehydrologyandsoilphysicsno-
chemistry more immediately accessible to tationusedinChapter2(ChemicalHydrology)
studentstrainedinpurechemistry. and elsewhere follow Hillel (2004) in Intro-
There are a few exceptions, the first ductiontoEnvironmentalSoilPhysics.
relating to partition constant notation. The Water residence time and water budgets
environmental science community uses haveimportantimplicationsforenvironmen-
a special notation for the octanol-water talchemistry.Chapter2(ChemicalHydrology)
partition constant that explicitly identifies now includes a discussion of elementary
octanol as the organic phase involved in potential evapotranspiration models that al-
physisorption by partition. Identifying the lowscientiststocomputeapproximatewater
adsorbent is essential for the environmen- budgets and estimate soil water residence
tal science community because the same timeusingreadilyavailabletemperatureand
adsorptive will yield different partition precipitationdatafromthousandsofweather
constants for partitioning into octanol, the stationsworldwide.Therearealsosignificant
fattytissueoflivingorganisms(inthecaseof revisionsoftheplate-theorytransportmodel
bioconcentration factors), adsorption by the that will hopefully make the discussion of
solid phase soils, sediments or aquifers, and thismodelmoretransparent.
adsorptionbytheorganiccarboncomponent Reviewers requested further details on
in the same. IUPAC does not identify the mechanisms of silicate mineral chemical
the organic phase in their recommended weathering. Chapter 3 (Clay Mineralogy and
partition constant (Kφ) and, hence, the Chemistry) now includes a discussion of the
D A
IUPAC recommended partition constant solid-state transformation and surface-site
symbol is unable to represent legitimate limited reactions that many mineralogists
distinctionsrecognizedbytheenvironmental believe explain the formation of low-
sciencecommunity. temperaturelayersilicatesthroughchemical
xiii
xiv
SECONDEDITIONPREFACE
weathering. This chapter also discusses the and Adsorption) by drawing distinctions
origins of silicate mineral alkalinity that between physisorption and chemisorption,
is essential for the later chapter on acid- and importance of molecular association
base chemistry. Finally, the discussion of in organic matter extracts. The associative
clay swelling was completely rewritten to behavior of extracted organic matter is a
provideamoresoundfoundationtothisvery key factor in the physisorption of organic
importantphenomenon. substances by dissolved and adsorbed
Chapter 4 (Ion Exchange) immediately organicmatter.Chapter8nowincludesadis-
follows the chapter on clay chemistry. cussionofadsorptionedgefittingandanex-
This chapter now includes a thorough panded evaluation of surface-complexation
discussion of the Vanselow mole-fraction models.
and the Gaines-Thomas equivalent-fraction Reconciling the pure chemistry perspec-
conventions,demonstratingboththedistinc- tive of reduction-oxidation chemistry with
tions between the two equilibrium quotient thebiologicalanaerobiosisdrivingreduction
expressionsandtheirunderlyingunity.More in soils and sediments is an important
advancedtopics,suchastheroleofrealand addition to Chapter 9 (Reduction-Oxidation
ideal mixtures in the ion exchange process Chemistry). This discussion provides a
andthefatalflawsoftheGaponconvention, rational basis for the relative efficiency of
appearinappendixes. ferricironrespirationandsulfaterespiration
Chapter 5 (Water Chemistry) places less and allows a deeper understanding of
emphasis on R.I.C.E. tables, scaling back the restrictionsoncarbon-useefficiencyimposed
discussion and moving it to an appendix. byanaerobicrespiration.
This edition discusses the steps students Chapter 10 (Human Health and Ecological
can take to design input files that will Risk Analysis) now includes a more sound
faithfully simulate the chemistry of the justification for the profoundly different
component species and the importance of treatmentofcarcinogensandnoncarcinogens
evaluating water analyses for reliability, a in risk analysis: the irreversible adverse
theme continued in Chapter 6 (Acid-Base effect of carcinogen intoxication and the
Chemistry). Chapter 6 includes an expanded presumedreversibleeffectsofnoncarcinogen
discussion of alkalinity and methods for intoxication. A brief discussion of ecotox-
incorporating alkalinity in water chemistry icity risk assessment reveals the parallels
simulations. between human health and ecological risk
Chapter7(NaturalOrganicMatter)isnow assessment.
positionedbeforethechapteronadsorption, The number of chapter exercises is
followingthelogicofpositioningclaychem- expanded by about half to more than one
istry before ion exchange. This chapter be- hundred exercises. None of the chapter
gins with a brief review of natural organic exercisesincludesolutions;exercisesolutions
matter research for the past 100 years. The appear in the Instructor’s Manual (http://
secondeditionexpandsthediscussionofbe- booksite.elsevier.com/9780128041789/) that
low ground carbon cycle models and now accompanies thesecond edition.Thesecond
includes a discussion linking carbon-use ef- edition also attempts to strike a balance
ficiencytothemeancarbonreductioninnat- between topics appropriate for undergrad-
uralorganicmatter. uates with limited chemistry experience
Some of the topics raised in Chapter 7 and more advanced topics intended for
areexpandedinChapter8(SurfaceChemistry moreadvancedundergraduatestudentsand
xv
SECONDEDITIONPREFACE
graduatestudentswhoarenotspecializingin “Bill” Hickey, Robert W. Taylor, Beat Müller,
chemistry.Advancedtopicsgenerallyappear Francisco Arriaga, Birl Lowery, and Alfred
inappendixesattheendofeachchapter. Hartimink.
Iwishtothankthefollowingcolleaguesfor WilliamF.Bleam
their assistance and encouragement: Willim Madison,Wisconsin
C H A P T E R
1
Element Abundance
O U T L I N E
1.1 Introduction 1 1.7 Element Abundance Frequency
Distributions 20
1.2 ABriefHistoryoftheSolarSystem
andPlanetEarth 3 1.8 Estimating the Central Tendency
of Logarithmic-Normal
1.3 Elemental Composition of Earth’s
Distributions 25
LithosphereandSoils 4
1.3.1 RelativeElementalAbundance 4 1.9 Summary 32
1.3.2 ElementsandIsotopes 6
Appendices 32
1.3.3 NuclearBindingEnergy 7
1.AFactorsGoverningNuclearStability
1.4 Enrichment and Depletion During
andNuclideAbundance 32
PlanetaryFormation 12
1.A.1 TheTableofNuclides 32
1.4.1 PlanetaryAccretion 12
1.A.2 NuclearMagicNumbers 34
1.4.2 PlanetaryStratification 13
1.B RandomSequentialDilutionandthe
1.5 TheRockCycle 17
LawofProportionateEffect 35
1.6 SoilFormation 19
References 37
1.1 INTRODUCTION
StudentsencounterthePeriodicTableoftheElementsasearlyashighschoolandbycollege
have come to understand the periodicity underlying its design, to associate letter symbols
with atomic numbers, and how to find the atomic mass and electron configuration of each
element.Whileitislikelystudentswillbefamiliarwiththeisotopeconceptandunderstand
1
SoilandEnvironmentalChemistry ©2017ElsevierInc.Allrightsreserved.
http://dx.doi.org/10.1016/B978-0-12-804178-9.00001-X
2
1.ELEMENTABUNDANCE
TABLE1.1 IntegerAtomicMassesforElementsThatHaveNoStable
Nuclides
AtomicNumber(Z) ElementSymbol ElementName AtomicMass
43 Tc Technetium 98
61 Pm Promethium 145
84 Po Polonium 209
85 At Astatine 210
86 Rn Radon 222
87 Fr Francium 223
88 Ra Radium 226
89 Ac Actinium 227
what determines atomic mass of an element,1 it is unlikely they are familiar with the Table
ofNuclides.
Theofficialatomicmasses,appearinginareportreleasedbyInternationalUnionofPureand
AppliedChemistry(IUPAC)(Wieser,2007),arebasedonisotopicabundancescompiledbyan-
otherIUPACcommission(Bohlkeetal.,2005).Carefulinspectionoftheatomicmasseslistedin
thePeriodicTableoftheElementsrevealsthat,forsomeelements,theatomicmassisassigned
integer atomic mass rather than adecimal atomic mass. These elements appear inTable 1.1.
Severalotheractinideelements(thoriumTh,protactiniumPa,anduraniumU)areidentifiedas
havingnostableisotopesyetIUPACquotesdecimalatomicmasses.Acompleteunderstanding
ofatomicmassandisotopestabilityrequiresinformationcompiledintheTableofNuclides.
ThePeriodicTableoftheElementsimpliestheexistenceofallnaturallyoccurringelements
from hydrogen to uranium and it is reasonable to assume these elements exist on planet
Earth. In fact, every sample of water, rock, sediment, and soil contains every stable element
and many of the unstable elements. The Periodic Table of the Elements, however, fails to
provide sufficient information to understand natural abundance in the Universe, the Solar
System,andplanetEarth.
Naturalelementalabundancehasotherimplicationsbesidescosmologicalandgeological
chemistry. The Environmental Working Group published an article in October 2008 entitled
“Bottledwaterqualityinvestigation:10majorbrands,38pollutants”(Naidenkoetal.,2008).
AmongthepollutantsfoundinbottledwatersoldintheUnitedStateswasradioactiveSr-90
(0.02 Bqdm−3),2 radioactive radium3 (0.02 Bq dm−3), boron (60–90 mg dm−3), and arsenic
1Theatomicmassofanelement,asitismostcommonlyreported,isaweightedaverage.Itmultipliesthemass
ofeachstableisotopetimesitsrelativeabundance(Bohlkeetal.,2005).
2StrontiumisthenamegiventotheelementwithatomicnumberZ=38.Strontium-90(9308Sr52)istheunstable
(i.e.,radioactive)nuclidewithatomicnumberZ=38,massnumberA=90,andneutronnumberN=52.
StrontiumisotopesincludeallnuclideswithatomicnumberZ=38.
3Radioactiveradiumisreportedasthecombinedactivityoftwounstableradiumisotopes:22868Ra138and
28288Ra140.
3
1.2 ABRIEFHISTORYOFTHESOLARSYSTEMANDPLANETEARTH
(1mgdm−3).Thereportedconcentrations,combinedwithacommentarylistingthepotential
andactualtoxicityofthesesubstances,canbealarming.Theimportantquestionisnotwhether
drinking water, food, air, soil, or dust contains toxic elements; it most certainly does! The
importantquestionsare:Istheconcentrationofatoxicelementindrinkingwater,food,orsoils
elevatedrelativetonaturalabundanceorisitsufficienttoproduceanadversehealtheffect?
The US Environmental Protection Agency (USEPA) has established a maximum contam-
inant level (MCL) for beta emitters—such as strontium-90 or radium-228/radium-226—in
public drinking water: 0.296Bq dm−3, which is tenfold higher than the single detection
reportedbyNaidenkoetal.(2008).TheUSEPAdoesnothaveadrinkingwaterstandardfor
boron, but the World Health Organization recommends boron levels in drinking water less
than 500mg dm−3, and in 1998 the European Union adopted a drinking water standard of
100mgdm−3.TypicalboronconcentrationsinUSgroundwaterfallbelow100 mgdm−3 and
90%below40mgdm−3.
Of the contaminants featured by Naidenko et al. (2008), arsenic is the most troubling.
Naidenko et al. (2008) reported a single case of 1 ppb arsenic4 in bottled water; however,
the mean arsenic concentration in US groundwater5 is 13.9 μgdm−3 with a median arsenic
concentrationof1.4μgdm−3.TheoriginalUSEPAarsenicdrinkingwaterMCLof50μgdm−3
was lowered to the current MCL of 10 μgdm−3 in 2001.6 Natural arsenic abundance in US
groundwater means over 10% of the population is potentially exposed to arsenic at levels
exceedingthecurrentarsenicMCL.
Understandingtheprocessesthatdeterminerelativeelementalabundanceandthestatisti-
calmethodsneededtoestimatetheelementalcompositionofrocks,sediments,andsoilsare
themajorthemesofthischapter.
1.2 A BRIEF HISTORY OF THE SOLAR SYSTEM AND
PLANET EARTH
Gravitationalcollapseofaprimordialgasanddustcloudgavebirthtothepresent-daySolar
System.Conservationofangularmomentumintheprimordialcloudexplainstherotationof
theSunandtheprimordialaccretiondiskthatspawnedtheplanetsandotherbodiesthatorbit
theSun.
AccretionandradioactivedecayreleasedsufficientheattomelttheprimordialEarth,lead-
ingitsstratificationintoasolidmetalliccore,amoltenmantle,andacrystallinelithosphere.
PlanetaryaccretionandstratificationalteredthecompositionofEarth’slithosphererelativeto
theprimordialcloudandimposedvariabilityinthecompositionofeachelementasadirect
consequenceofeachdifferentiationprocess.
Throughout its entire history, planet Earth has experienced continual transformation as
plate tectonics generate new oceanic lithosphere and shift continental lithosphere plates
aroundlikejigsawpuzzlepieces.Platetectonicsandthehydrologiccycledrivearockcyclethat
41ppb=1μgdm−3.
5Geometricmeanbasedonover7199samples(NewcombandRimstidt,2002).
6http://water.epa.gov/lawsregs/rulesregs/sdwa/arsenic/regulations.cfm(September17,2015).
