1. Environmental Chemistry
Chapter 6:
Environmental Organic Chemistry
Copyright © 2009 by DBS

2. Contents Introduction The Diversity Of Organic Compounds
The Fate of Organic Compounds
Chemical Partitioning
Chemical Transformation and Degradation
Chemical Transformation Through Photochemistry
Conclusions

3. Environmental Organic Chemistry Introduction
EOC – Environmental Organic Chemistry
Study of both natural and man-made organic chemicals
Developed as an area of interest through developments in gas chromatography
‘Organic chemist’ – synthesizes organic chemicals under lab conditions, produces highest possible yield, at a designated purity
‘EOC’ – works under Earth’s near surface conditions, quantifies the same chemicals, by-products from environmental media (e.g. soil, water, biota)

4. Environmental Organic Chemistry The Diversity of Organic Compounds
Categorized according to molecular weight, volatility and/or reactivity

5. Environmental Organic Chemistry The Diversity of Organic Compounds
Categorized according to molecular weight, volatility and/or reactivity
More volatile C1-C6 compounds have impact on atmospheric photochemistry
Oxidation of alkanes with OH radical to form peroxy (HO2) and alkoxy (RO2) radicals important for converting NO to NO2 and formation of ozone (Chp. 2)
Compounds of higher molecular weight react o to form hydroxyl carbonyl products which comprise organic aerosols
Semi-volatile organic compounds include the persistent organic pollutants (POP’s), aliphatic compounds (C chains >C15), normal, branched and cyclic alkanes and polycyclic compounds
Humic substances in soils

6. POP’s
Phase out of POP’s by the 2004 Stockholm Convention

7. Environmental Organic Chemistry The Diversity of Organic Compounds
Over 217,000 contaminated sites have been identified by EPA
Chlorinated phenols and organochlorines enter the environment as emissions from manufacture, incineration, use as a wood and leather preservative (Creosote) and biocide. - find their way into soil, sludges and sediments)
The scale and complexity of remediation sites pose problems in applying common treatment processes such as bioremediation
Incineration is effective, but can produce harmful chemicals during incomplete combustion. Projected cost is also high ($1200/ton).

8. Environmental Organic Chemistry The Diversity of Organic Compounds
Categorized according to molecular weight, volatility and/or reactivity

9. Environmental Organic Chemistry The Diversity of Organic Compounds
Identifying Sources of Hydrocarbons
Source appointment requires being able to distinguish between material of different origins (biogenic vs anthropogenic)
Carbon Preference Index (CPI) – concentration ration of odd:even numbered alkane chain lengths
e.g. recent biogenic n-alkanes favor odd-carbon numbered chain lengths, whereas aged organic material does not
CPI > 1 suggests that the aliphatic HC’s are biogenically derived
CPI < 1 suggests petrogenic (e.g. fossil fuel) derived sources
PAHs and their derivatives are used to distinguish between pyrolytic and petrogenic sources
Ratios of parent PAHs and parent PAH to alkylated versions may be used to identify petrogenic vs pyrolytic sources

10. Environmental Organic Chemistry The Fate Of Organic Contaminants
1000’s of organic chemicals of interest
EPA’s US Office for Pollution Prevention and Toxics (OPPT) maintains lists of high production volume chemicals as well as persistent bioaccumulative toxins (PBTs)
All must be risk assessed
Knowledge of both the usage (quantity released) and its behavior (transport, partitioning and transformation)
Once present in the environment EOCs are subject to two main processes:
Transport within and between phases
Chemical transformation driven by chemical and/or biochemical processes

12. Environmental Organic Chemistry Chemical Partitioning
Equilibrium partitioning
e.g.
between solid and liquid phases (dissolution)
Liquid and gas phases (volatilization)
Solution and solid (adsorption)
Solution and immiscible liquid (solvent partitioning)
Net transport of organic chemical between phases is quantified according to a partition coefficient (K)
K1,2 = C1/C2
Where C1 = concentration of chemical in phase 1, C2 = concentration of chemical in phase 2
Units are usually mol/L (mg/L) for liquids and mol/kg (mg/kg) for solids

13. Environmental Organic Chemistry Chemical Partitioning
Partition coefficient refers to one chemical species in each phase
Ionizable chemicals in water may be present in both neutral and dissociated forms, each would have a separate partition coefficient
For well-defined phases (pure water or pure liquid chemical) partitioning with another well-defined phase results in the use of the term partitioning constant (e.g. Henry’s Law constant)
Distribution ratios (e.g. soil-water distribution ratio Kd) describe partitioning between a heterogeneous solid phase (soil) and soil-water (containing a variety of compounds)
Distribution ratios account for all the speciated forms of a chemical and sorption mechanisms – it describes the distribution of a chemical rather than a partitioning

14. Environmental Organic Chemistry Chemical Partitioning
Important Partitioning Coefficients
Vapor pressure (solubility in air) and aqueous solubility explain the partitioning of chemicals
Kaw
Koa
Kow

15. Environmental Organic Chemistry Chemical Partitioning
Important Partitioning Coefficients
Octanol-water Partition Coefficient
(KOW) is a measure of the lipophilicity/hydrophobicity of a substance
KOW = concentration in octanol
concentration in water
Non-polar chemicals partition in octanol and give a high KOW
1000’s to 10,000’s, usually use log scale, pKOW

16. Environmental Organic Chemistry Chemical Partitioning
Dependence of KOW on increasing molecule size
Contaminant
KOW
Mol. Weight
Benzene
2.13 78
Napthalene
3.35
128
Phenanthrene
4.57
178
Pyrene
5.18
202
Benzo(a)pyrene
252
Dec. aqueous solubility

17. Environmental Organic Chemistry Chemical Partitioning
Chlorine substitution in organic compounds results in larger KOW values
Due to a steric effect
Contaminant
KOW
Mol. Weight
Benzene
2.13 78
Monochlorobenzene
2.8
113
Hexachlorobenzene
5.5
178
Dec. aqueous solubility

18. Environmental Organic Chemistry Chemical Partitioning
Bioconcentration – uptake of a chemical by an aquatic organism via respiratory surface (gils/skin)
BCF = bioconcentration factor (related to KOW)
Usually normalized to lipid content of the organisms to account for differences between organisms
Baird and Harrison

19. Environmental Organic Chemistry Chemical Partitioning
Bioconcentration factor, BCF
BCF = concentration of solute in organism
concentration of solute in water
From empirical studies:
BCF  KOW x % by weight of fat
(assumes fatty tissues have reached equilibrium, assume 5 % fat content)
For DDT
log KOW = 6 or
Kw=
BCF for DDT lies
Hence KOw can be used to predict BCF
Higher the KOw more
likely chemical is bound
to organic matter in soil
and fatty materials
See Bunce (1994) for a detailed look at pharmacokinetics

20. Question
Fish (5.0 % body fat) taken from a particular lake were tested and found to contain 200 ppm DDT in their tissues.
Determine the concentration of DDT (pKOW = 6.2) in this lake.
Log KOW = 6.2,  KOW = 106.2
BCF = KOW x (% body fat/100)
BCF = 1.6 x 106 x (5/100) = 7.9 x 104
BCF = concentration in fish / concentration in lake
Concentration in lake = 200 / 7.9 x 104 = 2.5 x 10-3 ppm = 2.5 ppb

21. Environmental Organic Chemistry Chemical Partitioning
Organic carbon to water partition coefficient (Koc)
Koc = Coc (mol/kg) / Cw (mol/L)
Units of Koc are L kg-1
Koc can be estimated from Kow according to an empirically derived relationship
Koc = 0.35Kow (units are L kg-1)
To describe partitioning as it relates to conc. Organic matter
Koc= Kd or Kp
Fraction of organic matter in sample
KOC = Kp/fOC

22. Environmental Organic Chemistry Chemical Partitioning
Lab work: solution of known pollutant mass and water, soil/sediment, or DOM is mixed together for 3 days
Solid and aqueous phases are separated by 0.45 μm filtration
Measurement in lab is an approximation!
Kd depends on pH, type of cations present, ionic strength, surface charge, solids-to-water ratio
Assumes reversible sorption

23. Environmental Organic Chemistry Chemical Partitioning
Table 3.2: Cd2+ on
sediment
Designates exp.
Measurements

24. Environmental Organic Chemistry Chemical Partitioning
Kp usually more constant
Methoxychlor (pesticide) on clay
Hydrophobic organic pollutant
Karickhoff et al., 1979

25. Environmental Organic Chemistry Chemical Partitioning
Hydrophobic pollutants sorb more with greater OM content
Slope here is: Kp/fOC = KOC
Karickhoff et al., 1979

26. Environmental Organic Chemistry Chemical Partitioning
Important Partitioning Coefficients
Henry’s Law Constant and Air-Water partitioning (Kaw)
Henry’s Law constant (H, units Pa/mol m3 )
H = p / Cw
Where p = partial pressure of chemical in air (Pa), Cw = concentration in water (mol/m3)
If PV = nRT
n/V = Ca = P/RT
If Kaw = Ca/Cw = P/RTCw

27. Environmental Organic Chemistry Chemical Partitioning
Important Partitioning Coefficients
Henry’s Law Constant and Air-Water partitioning (Kaw)
Henry’s Law constant for organic chemicals varies tremendously
e.g. short chain alkanes with high VP and low aqueous solubilities have high H compared to alcohols which have lower VP and higher aqueous solubility
Pesticides generally have low VP, but lower solubility can result in high H values, these chemicals appreciably partition to air from bodies of water

28. Environmental Organic Chemistry Chemical Partitioning
Pesticides generally have low VP, but have very much lower solubility, can result in higher than expected H values, these chemicals appreciably partition to air from bodies of water

29. Environmental Organic Chemistry Chemical Partitioning

30. Environmental Organic Chemistry Introduction
Octanol-Air Partition Coefficient A

31. Environmental Organic Chemistry Introduction
Temperature Dependence A

32. Environmental Organic Chemistry Introduction
Partition Maps A

35. Environmental Organic Chemistry Chemical Transformation and Degradation

36. Environmental Organic Chemistry Chemical Transformation Through Photochemistry

37. Environmental Organic Chemistry Chemical Transformation Through Photochemistry

38. Environmental Organic Chemistry Chemical Transformation Through Photochemistry

39. Environmental Organic Chemistry Chemical Transformation Through Photochemistry

40. Environmental Organic Chemistry Chemical Transformation Through Photochemistry

42. Environmental Organic Chemistry Summary

43. References Karickhoff et al., 1979
Mackay, D. (1982) Environmental Science and Technology, Vol. 16, pp
Maldonado, C. et al (1999) EST, Vol. 33, pp
Schwarzenbach, R.P., Gschwend, P.H. and Imboden, G.M. (2003) Environmental Organic Chemistry, 2nd ed., Wiley Interscience.
Yunker, M.B. and Macdonald, R.W. (2003) Organic Geochemistry, Vol. 33, pp