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ENVIRONMENTAL
CHEMISTRY
Chem. 3030
The two terms ‘environmental chemistry’ and
‘pollution’ often seem to go together, yet
environmental chemistry is much more than the
study of chemical effects of pollution.
It is a multidisciplinary science of chemical
phenomena in the environment involving
chemistry, physics, life science, public health,
engineering, etc.
THE COURSE OUTLINE
Stratospheric chemistry and the ozone layer; principles of photochemistry, light
absorption by molecules, noncatalytic and catalytic process of ozone distraction, free
radicals, Cl and Br as X catalysts, the ozone hole and its consequences,
chlorofluorocarbons (CFCs).
Ground-level (tropospheric) air chemistry; ground-level ozone and photochemical
smog, oxidation of methane, hydrocarbons and atmospheric SO2, acid rain, ecological
effects of outdoor air pollutants, indoor air pollution: formaldehyde, NO2, CO, tobacco
smoke, asbestos, radioactivity from radon gas.
The greenhouse effect and global warming; energy absorption, the major and minor
greenhouse gases: CO2, water vapour, methane, N2O, CFCs.
Environmental consequences of energy use: CO2 emissions, solar energy,
conventional and alternative fuels, nuclear energy.
The chemistry of natural waters; acid-base chemistry, CO2/carbonate system, ion
concentations, alkalinity, seawater, redox chemistry in natural waters, oxygen
demand, the pE scale, sulphur and nitrogen compounds, ion complexes, stratification,
precipitation.
Soil chemistry; soil components, weathering process, aerobic, anaerobic soils, watersediment-soil system.
Reading References:
W. vanLoon, S. J. Duffy; Environmental Chemistry, a Global
Perspective, 2nd ed.
Colin Baird; Environmental Chemistry
TG Spiro, WM Stigliani; Chemistry of the Environment
Course notes
THREE MAJOR ENVIRONMENTAL MEDIA: SURFACE WATERS, SUBSURFACE
WATERS (SOIL AND GROUND WATER), AND THE ATMOSPHERE
Each medium has its own distinct characteristics but they have also many similarities.
Few chemicals are restricted in their movement to one medium only –
chemical exchange must be considered.
WATER
WATER IS THE ELEMENT OF SELFLESS CONTRAST –
IT PASSIVELY EXISTS FOR OTHERS
… WATER’S EXISTENCE IS,THEREFORE, AN EXISTING-FOR-OTHERS
…ITS FATE IS TO BE SOMETHING NOT YET SPECIALIZED
… AND THUS IT SOON CAME TO BE CALLED
‘THE MOTHER OF ALL THAT SPECIAL’
Hegel, Philosophy of nature (1817)
WATER
PROPERTY
MAGNITUDE
CONSEQUENCE
HEAT CAPACITY Exceptionally high
4.19 kJ / kg K
a). Slows down temp.changes.
b). Heat transported around the globe
by ocean currents.
c). Influences climate
LATENT HEAT OF Exceedingly high
Stops the water temp. from changing
FUSION
333 kJ/ kg
rapidly when is around zero –
additional energy required to freeze
the water.
LATENT HEAT OF Highest of all substances Low water and heat loss to the
EVAPORATION
2260 kJ/kg
atmosphere
DENSITY
Maximum density at 40C Ice floats, insulating the water below
Decreases with
from cold.
increasing salinity.
Stratification of non-flowing waters
SURFACE
TENSION
Highest of all liquids
73 mN/m
Controls the size of raindrops, sea
waves, sprays, etc.
DISSOLVING
POWER
Exceptionally good
Dissolves nutrients and transports
them to plants.
TRASPARENCY
Relatively large
Absorbs in the ultraviolet and
infrared but transmits the visible
radiation required for photosynthesis
Model of water molecule
Ice crystal
Polymers of water molecules
demonstrating the ‘flickering
clusters’ model
The model of hydration
sphere of sodium – an inner
rigid water shell, an outer,
somewhat rigid floating in the
sea of ‘free’ water
STRATIFICATION
EPILIMNION
warmer, lower density, aerobic
CO2
H2CO3
HCO3-
SO42-
NO32-- Fe(OH)3
THERMOCLINE
CH4
HYPOLIMNION
cooler, more dense, anaerobic
H2S NH3 NH4+ Fe2+(ag) bacteria
SEDIMENTS
THE ACDITY OF WATER
THE ACIDITY OF WATER AND ANY AQUEOUS SOLUTION –
MEASURE OF CONCENTRATION OF HYDRONIUM IONS = pH
pH = -log [H3O+]
or simply
Autoprotolisis of water:
pH = -log [H+]
2H2O  H3O+ + OH-
K = [H3O+] [OH-] / [H2O] = 1.8 x 10-16 (250C)
What is the concentration of water in water?
1000g (1L) / 18g = 55.56 mol/L
K = [H3O+] [OH-] / 55.56
or K x 55.56 = [H+] [OH-] = 10-14 (250C)
KW
and pKw = pH + pOH = 14
ACIDITY OF THE SOLUTION
IDENTIFY THE SPECIES IN SOLUTION
ex.
sol. NaCl in water
sol. HCl in water
HOW CONCENTRATIONS OF IONS DEPEND ON EACH OTHER
ex.
Ka, Kb, Kw
for HCl and NaOH sol.
MASS BALANCE
ex.
For the fixed volume V  m ~ c
CHARGE BALANCE
ve+ = veSOLUBILITY OF GASES
X(g) = X(aq)
KH = [X(aq)] / px
- Henry’s Law
ACID-BASE CHEMISTRY IN NATURAL WATERS
THE CO2 / CARBONATE SYSTEM
CO32-

H2CO3
moderately
weak
strong base
acid
CO2 + H2O  H2CO3  2H+ + CO32LIME ROCKS – SOURCE OF CARBONATE IONS
The proportion of the carbonate present in all its possible forms
NATURAL AIR,WATER,ROCK SYSTEM
AIR
CO2
WATER
H2CO3
HCO3- + H+
CO32- + H2O
+
Ca2+
ROCK
SOIL
SEDIMENTS
CaCO3
HCO3- + OH-
H20
EQUILIBRIUM: WATER / CaCO3
1. CaCO3  Ca2+ + CO32Ksp = [Ca2+] [CO32- ] = 4.6 X 10 –9 (250C)
Ksp = S2, S = (Ksp)1/2 = 6.8x 10-5M
[Ca2+] = [CO32- ] = S - solubility,
2. CO32- + H2O  HCO3- + OHK = [HCO3-] [OH- ] / [CO32- ]
3. = (1 + 2)
CaCO3 + H2O  Ca2+ + HCO32- + OH-
and KT = Ksp + K
Ka (HCO3-) = 4.7 x 10-11
and
Ka x Kb = KW = 10-14
Kb (CO32- ) = KW / Ka = 2.1 x 10-4
conjugate base
KT = [Ca2+] [HCO3-] [OH- ] and S = [Ca2+] = [HCO3-] = [OH- ]
KT = S3 = 9.7 x 10-13  S = 9.9 x 10-5
GREATER SOLUBILITY BECAUSE CO32 REACTS WITH WATER
EQUILIBRIUM: WATER / CaCO3 / CO2 (ATMOSPHERIC)
CaCO3 + CO2 + H2O  H2CO3  Ca2+ + 2HCO3with K = Ksp x Ka x Kb x KH/ KW = 1.5 x 10-6 M3/L3atm


and K = [Ca2+] [HCO3-]2 / p CO2
= S x (2S)2 / p CO2
p CO2 – partial pressure of atmospheric CO2 = 0.00036 atm
S3 = 1.3 X 10-10
Compare:
and
S = 5.1 x 10-4 M / L
water with CO2
[Ca2+]  5.1 x 10-4 M / L
without CO2
9.9 x 10-5 M / L
WATER WITH DISSOLVED CO2 MORE READILY DISSOLVES CaCO3
ACIDITY OF NATURAL WATERS – normal and acid rain
(1)
(1)
pH = 5.6
ACIDITY OF NATURAL WATERS – sea water
ACIDITY OF NATURAL WATERS - seawater
1
2
3
4
5
6
5
7
2
1
pH = 8.4
METAL COMPLEXES IN NATURAL WATERS
APPLICATION OF CHEMISTRY OF SIMPLE METAL - LIGAND SYSTEMS
TO MUCH MORE COMPLEX ENVIRONMENTAL SYSTEMS
EX: Inorganic Hg complexes in sea water
Conditions: pH = 8.4 – OH- , major anion ClCl-
and
Hg2+ + Cl-  HgCl+
OH-
HgCl+ + OH-  HgOHCl
HgCl+ + Cl-  HgCl2
and
HgOHxClyz
HgCl3-
HgCl42-
Large number of equilibrium reactions are occurring in water
In order to assess the environmental impact of trace metals in water body
predictions have to be made as to which species are present in solution.
Solutions: Complicated computer modeling and/or
graphical representations
THE MAJOR COMPLEXES OF TRACE METALS IN WATERS
COMPLEXES
COMPLEXES
Hg
Pb
Cu
Hg
Ni
Ag
Cu
Pb
ADSORBED
Na
Ag
K
FREE IONS
FRESHWATER
ADSORBED
Na
K
Ni
FREE IONS
SEAWATER
ELEMENTS PREDICTED TO HAVE
SIMILAR SPECIATION IN FRESH AND SEAWATER
ELEMENT
MAJOR SPECIES
ELEMENTS PREDICTED TO HAVE
DIFFERENT SPECIATION IN FRESH AND SEAWATER
FRESHWATER
BOTH
SEAWATER
REDOX CHEMISTRY IN NATURAL WATERS
The concentration of electrons control redox processes in the environment
pE = -log [e-]
Most common measure of electron activity is EH,
the electrode potential measured against SHE
The natural limits of redox in natural waters
The oxidation of water
H2O = O2 + 4H+ + 4e-
log K = - 83.1
The reduction of water
2H+ + 2e- = H2
K = pO2 [H+]4 [e-]4
and
K = pH2/ [H+]2 [e-]2
pE = 20.75 -pH
pE
log K =0
and
pE = -pH
pE
pH
pE and EH are linearly related:
pH
pE = (F/ 2.3RT) EH
REDOX AND ACIDITY CONDITIONS IN NATURAL WATERS
pE – pH (or EH - pH) DIAGRAMS (Pourbaix diagrams)
pE – pH (or EH - pH) DIAGRAMS (Pourbaix diagrams)
WATER CHEMISTRY...
AND SOIL
Soil composition
1. Inorganic mineral matter (defined as soil material made up mostly of oxygen,
silicon, and aluminum (many other metals in small quantities may be included)
2. Organic mineral matter (defined as soil material having derived mostly from
plant residues and made up mostly of carbon, oxygen, and hydrogen)
3. Solutes (refers to the portion of soil composed of water and mostly dissolved
salts (plant nutrients)
4. Air (refers to the gaseous portion of soil composed of the same gases found
in the atmosphere (oxygen, nitrogen, and carbon dioxide) but in different
proportions)
WATER CHEMISTRY... AND SOIL
Soil modifies water chemistry or quality through the processes of:
1. Surface-exchange hydrolysis
2. Dispersion by monovalent metal ions
3. Soil's catalytic role in many chemical and/or electrochemical
reactions
4. Precipitation reactions of heavy metals through hydroxylation
5. Oxidation reactions of organics and inorganics
6. Hydrolysis reactions of organics and inorganics
7. Condensation reactions of organics
8. Physical adsorption of metals and metalloids
9. Chemical reactions with metalloids
10. Soil-dissolution reactions
Overall, soil systems behave as complex biomolecular sieves.
Soil – polymeric structures of
silicates – extended networks
Si4+ can be replaced by Al3+
Other major cations:
H+, K+, Na+, Mg2+, Ca2+, Fe2+
Structural units in silicate minerals
ION EXCHANGE EQUILIBRIA ON THE SURFACE OF SOIL-CLAY PARTICLE
Clay minerals – particles <2µm.
They bond electrostatically cations – natural ion exchangers
Organic matter – humus:
decompose by organisms plant material in forms of cellulose and
hemicellulose
undecomposed –protein and lignin and its polimerized and partly
oxidized forms containing carboxylic groups –COOH: fulvic and
humic acids
Fulvic acid – soluble in alkaline and acidic solution
Humic acid - soluble in alkaline, not soluble in acidic solution
Humic materials have great affinity to heavy metal cations and
extract them from waters by ion exchange process – formation
of complexes by –COOH groups in fulvic and humic acids
CEC – Cation Exchange Capacity – quantity of cations that are
reversibly adsorbed per unit mass of a dry soil – number of
moles of positive charge
WEARTHERING PROCESS
DISSOLUTION AND DEPOSITION PROCESSES
SUSPENDED
WATER
SEDIMENTS
SEDIMENTATION
DISSOLUTION
RESUSPENSIBLE
BOTTOM
BOTTOM
SEDIMENTS
SEDIMENTS
THE INTERCHANGE OF MATERIAL BETWEEN SEDIMENTS AND WATER
SOIL CHEMISTRY
TRRESTIAL CHEMISTRY
WATER-SOIL CHEMISTRY
BIOGEOCHEMISTRY
DISSOLUTION AND DEPOSITION PROCESSES:
 SOLUBILITY AND PRECIPITATION
 CHEMICAL WEATHERING
- BY HYDROLISIS (SILICATES)
- BY OXIDATION (IRON MINERALS, S2-)
 COLLOIDS AND THEIR AGGREGATION
- HYDROPHILIC COLLOIDS (LARGE MOLECULES
WHICH INTERACT STRONGLY WITH WATER)
- HYDROFOBIC COLLOIDS (INTERACT LESS STRONGLY
BUT ARE STABLE BECAUSE PARTICLES REPEL EACH OTHER
- ASSOCIATION COLLOIDS (MICELLES)
CONCENTRATION OF IONS IN SOIL SOLUTIONS IS DETERMINED
BY MANY PROCESSESS DEPENDENT ON EACH OTHER
REDUCTION
DESORPTION
PRECIPITATION
OXIDATION
COMPLEX
FORMATION
ACID-BASE
REACTION
ADSORPTION
OTHER CONNECTIONS….?
REMOVING COLLOIDAL MATERIAL  TO AGGREGATE COLLOIDS  TO
DESTABILIZE COLLOIDS 
ACID MINE DRAINAGE
ACID MINE DRAINAGE
This reaction is catalyzed by bacteria.
The pollution associated with AMD is characterized by:
1.
Seeping from mines acidified water and rust-coloured iron hydroxide
2.
The concentrated acid liberate toxic heavy metals from their ores in the
mine, further adding to the pollution.
CHEMICAL SPECIATION OF HEAVY METALS
THE NEED FOR SPECIATION
DISTRIBUTION,
MOBILITY AND BIOLOGICAL AVAILABILITY OF CHEMICAL
ELEMENTS DEPENDS NOT SIMPLY ON THEIR CONCENTRATIONS BUT, CRITICALLY,
ON THE CHEMICAL AND PHYSICAL ASSOCIATIONS WHICH THEY UNDERGO IN
NATURAL SYSTEMS.
 CHANGES IN ENVIRONMENTAL CONDITIONS (NATURAL AND ANTHROPOGENIC)
CAN STRONGLY INFLUENCE THE BEHAVIOUR OF BOTH ESSENTIAL AND TOXIC
ELEMENTS BY ALTERING THE FORMS IN WHICH THEY OCCUR.
THE
MOST IMPORTANT CONTROLING FACTORS INCLUDE pH, REDOX
POTENTIAL, AND AVAILABILITY OF ‘REACTIVE SPECIES’ SUCH AS COMPLEXING
LIGANDS (ORGANIC AND INORGANIC), PARTICLE SURFACES FOR ADSORPTION,
AND COLLOIDAL MATTER.
SPECIATION SCIENCE SEEKS TO CHARACTERISE, AT LEAST SOME OF,
THE MOST IMPORTANT FORMS OF AN ELEMENT, IN ORDER TO
UNDERSTAND THE TRANSFORMATIONS BETWEEN FORMS WHICH CAN
OCCUR, AND TO INFER FROM SUCH INFORMATION THE LIKELY
ENVIRONMENTAL CONSEQUENCES.
CLASSES OF CHEMICAL SPECIATION
SCREENING SPECIATION
(identification and quantification
of different species of an element,
e.g. free ions, complexes)
REDOX SPECIATION
(identification and quantification
of different oxidation states
of an element)
ISOTOPIC SPECIATION
CHEMICAL
(mostly for medical purposes
SPECIATION
contaminants)
DISTRIBUTION SPECIATION
(e.g. biological uptake, transport
in soils, distribution in water
column)
or to trace sources of
CHEMICAL SPECIATION OF HEAVY METALS
FUTURE DEVELOPMENTS AND REQUIREMENTS
STANDARIZATION OF SPECIATION SCHEMES
DEVELOPMENT
OF NEW IN SITU ANALYTICAL METHODS FOR
SPECIES
DETERMINATION
DEVELOPMENT
OF INTELLECTUAL TOOLS NECESSARY TO FILL THE GAP
BETWEEN THE MOLECULAR AND THE MACROSCOPIC LEVELS
IMPROVEMENT OF THE IDENTIFICATION
AND QUANTIFICATION OF ‘ORGANIC
MATERIALS’
STUDY OF THE BEHAVIOUR AND PROPOERTIES OF COLLOIDAL MATTER
STUDY
OD THE ROLE PLAYED BY LIVING ORGANISMS IN TRACE METAL
CONTROL
DEVELOPMENT OF CHEMICAL SPECIATION SCHEMES WHICH CAN BE DIRECTLY
RELATED TO MEASURES OF BIOAVAILABILITY
CHEMICAL SPECIATION OF HEAVY METALS
GENERAL STRATEGIES FOR SPECIATION
 DISTURBANCE OF EQUILIBRIUM STATE
SAMPLING
PREPARATION STEPS
STORAGE
SEPARATIONS
DIRECT METHODS FOR DETERMINATION
INDIRECT METHODS FOR DETERMINATION
 SPECIATION BASED ON CALCULATION METHODS
SOLUTION OF MULTIPLE SIMULTANEOUS EQATIONS
# COMPETING CHEMICAL EQUILIBRIA
# MASS BALANCE RELATIONSHIPS ASSUMPTIONS
# NUMBER OF ‘SPECIES’
# ‘BEST VALUES’ OF THE VARIOUS EQUILIBRIUM CONSTANTS
COMPUTER MODELING
# SIMULATIONS
# PREDICTIONS
 EXPERIMENTAL vs CALCULATION METHODS
THE MODELING OF SPECIATION REACTIONS IN NATURAL SYSTEMS
PRINCIPLES OF CHEMICAL THERMODYNAMICS THAT CAN BE USED TO
PREDICT THE SPECIATION OF A GIVEN ELEMENT:
COMPLEX EQUILIBRIA
PRECIPITATION AND DISSOLUTION
ADSORPTION AND MINERAL PHASES
ACTIVITY COEFFICIENTS AND INTERFERENCES
ACIDITY AND ELECTRON BALANCE (pH, pE)
PHYSICAL PROPERTIES (TEMP. PRESSURE, UV, ETC.
THE RESULTS OF MODELLING ARE ONLY AS GOOD
AS THE ANALYTICAL DATA USED FOR CALCULATIONS!