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ES/RP 532Applied Environmental Toxicology
Lecture 2Environmental Analytical Chemistry
Chemical Functional GroupsPhysicochemical Properties
Professional Scientific Societiesfor Toxicology
Society of Toxicology (SOT) http://www.toxicology.org/
Society of Environmental Toxicology &Chemistry (SETAC) http://www.setac.org/
Goal of EnvironmentalToxicology
Predict the effects or impact of chemicaltechnologies on organism (ecosystems)
Conceptual Frameworks for UnderstandingFate & Effect of Environmental
Contaminants Environmental Chemodynamics Toxicodynamics
The Logical Process forDetermining Likelihood of Effects Risk Assessment
Hazard Identification Dose-response characterization Exposure assessment Risk characterization
What Is Needed toEstimate (Guess) The Risk?
Risk Assessment
Toxicology Environmental Chemistry
No Observable Effect Level
Exposure Assessment
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“Residues”
Residues refer to chemicalcontaminants in the physicalenvironment and in biological tissues The constituents of chemical products (or
formulations) become residues when theyare dispersed into the environment
Residue Amount Expressed as a concentration
Unit of mass per volume or surface areaMilligrams per Liter (mg/L) (or per square meter)Micrograms per milliliter (µg/mL) (or per sq. cm)
A proportion1% (1 part per 100)0.0001% (1 part per million)
A molar quantityMoles/L (if in solution)
– One mole = the molecular weight of a substance in grams– 1 µmol = the molecular weight in micrograms
What Does It Mean?
Usual range of detections manyenvironmental contaminants rangesfrom ppt (parts per trillion) - ppb (partsper million) From the perspective of purity, that
translates to 99.9999999999% -- 99.9999999% I.e., if 1 ppb = 0.0000001%, then 100%
minus 0.0000001% yields 99.9999999%
99.4% Pure!!!!!!!!
1950 1960 1970 1980 1990 2000
GramsPerLiterg/L ???
100
10-3
10-6
10-9
10-12
10-15
ppthppm
ppbppt
ppq
Year
Analytical Technology Has Advanced FasterThan Biological Understanding
BBBB
B
B
B
B
B
0
5
10
15
20
25
30
35
40
45
0.001 0.01 0.1 1 10
Atrazine Reporting Limit (µg/L)
% Frequency
Frequency of Atrazine Detection in Shallow AquifersIncreases as Reporting Limit Decreases
Kolpin et al. JEQ 25 (1996)
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Pesticide Residues--Frequencies/Identities/Concentrations
Method Detection Limit Method Quantitation Limit Concentrations
means medians geometric mean percentiles
Relevant Questions General Chemistry Review
Emphasis on Functional Groups&
The Concept of Polarity
# of Electrons in Shella
Name Symbol AtomicNumber
AtomicMass
1(K)
2(L)
3(M)
4(N)
5(O)
NetCharge of
Kernel
No. ofCovalent
BondsHydrogen H 1 1.008 1 1+ 1Helium He 2 4.003 2 0
Carbon C 6 12.011 2 4 4+ 4Nitrogen N 7 14.007 2 5 5+ 3, (4)c
Oxygen O 8 15.999 2 6 6+ 2, (1)d
Fluorine F 9 18.998 2 7 7+ 1Neon Ne 10 20.180 2 8 0
Phosphorus P 15 30.974 2 8 5 5+ 3,5Sulfur S 16 32.060 2 8 6 6+ 2, 4, 6, (1)c
Chlorine Cl 17 35.453 2 8 7 7+ 1Argon Ar 18 39.948 2 8 8 0
Bromine Br 35 79.904 2 8 18 7 7+ 1Krypton Kr 36 83.800 2 8 18 8 0
Iodine I 53 126.905 2 8 18 18 7 7+ 1Xenon Xe 54 131.290 2 8 18 18 8 0
Table 2. Electronegativities of Atoms (the greater the number the greater the EN)Charge of kernel1 +1 +4 +5 +6 +7
H2.2
Increasing Size of kernell
C2.5
N3.0
O3.5
F4.0
l
P2.2
S2.5
Cl3.0
l
Br2.8
l
I2.5
l
1 The kernel refers to the nucleus and the inner filled electron shells
Electronegativity (EN)
EN increases left to right across columns;EN decreases top to bottom across rows
e- e-
e-C
e-e-
e-
e-Ce-
Covalent Bonds
Formed between atoms by sharingelectrons
e-
e-e-
e-
e-
e-
e-
e-
e-
e-
C C
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Polarity (Polar Bonds) Owing to differences in electronegativity,
sharing of electrons in the bondingorbitals may be unequal, i.e., towardone atom or the other
Thus, positive (electron deficient) andnegative (electron rich) poles are set upbetween atoms in a molecule
C Oδ+ δ−
Ionic Bonding When atoms of very large differences in EN
bond, such as between column 7 andcolumn 1 or 2 elements, then the electronsmay be transferred from the atoms of lowestelectronegativity to the atoms of highestelectronegativity
Thus, the atoms of highest EN would have a“permanent” negative charge
The atoms of lowest EN would have a“permanent” positive charge
Na+ Cl-
O Hδ+δ−
Nδ−
Hydrogen Bonding When hydrogen (H) is bonded to O or N,
which are more electronegative, then therelatively positive H can be attracted to anelectronegative atom on nearby molecules Especially if the more EN atom has an unbonded
pair of electrons Forms a hydrogen bond; not as strong as
covalent or ionic bond, but it can form stablemolecular interactions
Geometry (Bond Angles) Atoms within molecules actually exist in
definite geometric spatial relationshipsto one another that are characteristic ofthe type of bond For ex., carbon atoms have four valence
electrons, each oriented toward the cornerof a tetrahedron;
C
N
Nitrogen often uses three valence electrons (with anunpaired electron available for bonding an electrondeficient species like H); its spatial geometry tends toby trigonal
Geometry (Bond Angles) Double bonds will make a molecule
more rigid, giving the atoms lessdegrees of freedom to flop around androtate about each other
C C
Geometry (Bond Angles) Aromatic structures (alternating double bonds
in ringed systems) tend to be planar (i.e., lessfree rotation of the carbon atoms) Characterized by delocalized ‘pi’ electrons that
can impart some electronegative character Aromatic structures also are more stable than
non-cyclic structures
Note that double bonds in linear structures also havedelocalized ‘pi’ bonds
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Dipole Moment
The overall polarity of a molecule depends onboth the presence of polar bonds and on thegeometry of the molecule Planar, trigonal, tetrahedral
The the determinant of overall polarity is thevector sum of the individual polar bonds (i.e.,dipole moment of individual bonds), which iscalled the molecular dipole moment
CH
HH Cl
C OO
Dipole Moment (p) = 0
http://www.chem.tamu.edu/organic/Spring99/dipolemoments.html
p = 6.2 X 10-30 C.mor
1.84 D (debyes)
Intermolecular Forces
Attraction betweenmolecules due toinstantaneous dipolemoments
Intermolecular Forces
Intermolecular Forces
Substance Molecular Mass Dipole Momentµ (D)
B oiling Point°K
propane, CH3CH2CH3 44 0.1 231dimethyl ether, CH3OCH3 46 1.3 248methyl chloride, CH3Cl 50 2.0 249acetaldehyde, CH3CHO 44 2.7 294acetonitrile, CH3CN 41 3.9 355
The various intermolecular interactions canexplain various physicochemical properties
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R1 NR3
R2amino (primary amine, R2 = R3 = H secondary amine, R3 = H tertiary amine, R1, R2, R3 = C
aniline if R =
-C-C-C-C-
R-OH
R-SH
R1-O-R2
R1-S-R2
alkyl (can be denoted by R)
hydroxy (alcohol, if phenol then R = )
mercapto (thiol, mercaptan)
ether
sulfide (thioether)
Functional Groups impart characteristics upon molecules thatare important in intermolecular interactions and reactivity
R1 C R2
O
carbonyl (ketone, aldehyde when R 2 = H
R C OH
O
carboxy (carboxylic acid)
R1 C O R2
O
ester (carboxylic acid ester)
R1 C S R2
O
thioester
R1 C N
OR2
R3
amide
R C N cyano (nitrile)
phosphate ester (if X = O); thiophosphate ester (if X = S)
nitro
R N O
R NO
O
P O R3R2 O
R1 O X
nitroso
H3C CH2 CH3
Saturation
CH3H3C CH2
Unsaturation
ortho meta para
1 2345
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anthracene
Vapor Pressure The pressure of the vapor of a
compound at equilibrium with its purestate Think of VP as the escaping tendency of
the molecules of a pure substance fromitself
Compound to compound variationsarise as a result of intermolecular forces
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Pressure Gauge
Solution of benzene
Vapor PressureRanges forSeveral Groups ofContaminants
Schwarzenbach et al. 1993
Smaller moleculesin homologousseries tend to havehigher VPs
Schwarzenbach et al. 1993
Vapor pressure tends todecrease with increasecarbon chain length
Vapor pressure isdependent onambient temperature
Schwarzenbach et al. 1993
Water Solubility
The amount of a substance thatdissolves in a given quantity of water ata given temperature to form a saturatedsolution Think of it as the escaping tendency of
molecules from one another when placedin water
Limitations to Water Solubility Regular, highly ordered structure of water
Results from high degree of hydrogen bonding Cause of very high surface tension for such a
small moleculeSurface tension is the intermolecular, cohesive
attraction between like molecules of a liquidthat cause it to minimize its surface area
Causes the high boiling point of water A solute dissolving in water has to disrupt the
orderly structure of water (with consequentenergy costs) Think of it as punching a hole in the water
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O
H H HH
O
HH
O
HH
O
HH
O
HH
O
HH
O
HH
O
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diph2o.html#c3
Highly ordered structure ofwater due to extensivehydrogen bondingbetween molecules
Imbalance of intermolecular forces at“edge” of water tends to draw outerlayer of molecules into the interior,thereby reducing the surface area.
The water molecules inthe interior of the liquidare attracted equally inall directions.
Surface tension is the measure of inward forces at the surfacethat must be overcome to expand the surface area of the liquid.
Solutes (for ex., any contaminantin water) disrupt the waterstructure. That is, theintermolecular forces betweenwater molecules are disrupted.
If contaminant has functional groupsthat can hydrogen bond with water,then the water structure is disruptedless and more of the contaminant candissolve in the water (comparativelyless free energy in the system) Schwarzenbach et al. 1993
Change in HeatContent
Schwarzenbach et al. 1993
Facilitation & Limitationsof Water Solubility
If a dissolving molecule has functional groupsthat allow hydrogen bonding, then theregularity of the water structure is disruptedless than if the molecule lacked the capabilityof hydrogen bonding
If no polar functional groups, than moreenergy must be expended to disrupt thewater structure Thus, entropy would necessarily be higher, and
consequently, WS would be less
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Examples of WaterSolubility Rangesfor DifferentGroups ofContaminants
Schwarzenbach et al. 1993
Distilled Water vs. SeawaterCompound Solubility, distilled H2O (ppm) Solubility, seawater (ppm)toluene 506.7± 6.1 418.5 ± 5.0acenaphthene 2.42 ± 0.02 1.84 ± 0.04pyrene 0.13 ± 0.01 0.09 ± 0.01
Effect of Temperature on Solubilitylog solubility (ppb)
Compound Molar Volume (mL) 15°C 20°C 25°Ctoluene 109 5.61 5.61 5.62acenaphthene 150 2.33 2.74 3.26pyrene 172 1.75 1.85 1.95
Rossi & Thomas, Environ. Sci. Technol. (1981), p. 715
Other dissolved substances can affect watersolubility of a compound. Solubility can befacilitated by the co-dissolved solvent re-orientingthe water structure so that the compound “fits” intothe water structure in a more thermodynamicallyfavorable manner.
Schwarzenbach et al. 1993
Schwarzenbach et al. 1993
Schwarzenbach et al. 1993
Recall that solution pH is the negative logarithm of the hydrogen ion [H+]concentration. H20 <====> H+ + OH-
H+ + H2O <===> H3O+, and K = 1 at equilibrium; Kw = [H+] x [OH-] = 1 x 10-14 M (the ion product constant for water)
For any acid (or base):HA + H2O <====> H3O+ + A-
Ka = [H + ][A − ]
[HA]= acidity dissociation constant
pH=pKa + log[A− ][HA]
pKa can be thought of as a measure of the tendency of an acid to dissociate (i.e.,deprotonate); by the same analogy, pKb is the tendency of a base to protonate
pKa (and pKb) can be thought of as the tendency of an acid to dissociateor a bases to accept a proton (H+). When pH = pKa, the concentration ofA- (the salt form) and HA are equal.
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Schwarzenbach et al. 1993
Note that protondissociation wouldonly occur atunrealistically highpHs.
Schwarzenbach et al. 1993
pH influences the relative abundance of the species of an organic acid,especially those with more than one acid or base functional group.
Schwarzenbach et al. 1993
Molar Volume
The volume occupied by one mole of asubstance in the gas phase. Regarding liquids and solids, the molar
volume is the volume occupied by a moleof substance in aqueous solution
In a very dilute solution, the molar volumeapproaches that of water (18 x 10-6 m3/mol)
Correlated with WS and VP
Schwarzenbach et al. 1993
As molar volume increases, the entropy for dissolutionalso increases because more energy has to be put intothe system to reorganize the water.
Schwarzenbach et al. 1993