Chemical Transformations

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Chemical Transformations

• AE 520
• Carl E. Anderson

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Transformation and Degradation Processes

• Biological Transformations due to microorganisms
• aerobic
• anaerobic
• facultative
• Most Important

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Transformation and Degradation Processes

• Chemical Transformations
• Hydrolysis
• Oxidation-Reduction
• Photochemical Processes
• Only in the presence of light
• Only on or near the surface

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Major Factors Influencing Chemical Transformation

• Microbial Concentration
• Biological Rates increase with increased active
  population
• No effect on non-biological transformation

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Major Factors Influencing Chemical Transformation

• Chemical Concentration
• Biological Rates usually increase unless the
  chemical is toxic
• Non-biological rates may increase, but it depends
  on the particular reaction.

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Major Factors Influencing Chemical Transformation

• Temperature
• Biological Rates will increase with temperature
  within the range tolerated by the organisms
• Non-biological Rates increase with increased
  temperature

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Major Factors Influencing Chemical Transformation

• Oxygen
• Determines the types of organisms and degradation
  pathways for Biological Transformations
• It is a potential reactant for chemical
  transformation.

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Major Factors Influencing Chemical Transformation

• Nutrients
• These are needed for microbial metabolism. Thus
  they are needed for Biological Transformation
• Not important for non-biological transformations

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Major Factors Influencing Chemical Transformation

• Inorganic and organic composition
• Organic carbon may support microbial populations
  and affect bioavailability.
• These are potential reactants and catalysts for
  non-biological processes. May affect availability

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Major Factors Influencing Chemical Transformation

• pH
• Affects microbial population composition
• Affects bioavailability of the chemical
• Major effect on hydrolysis
• probable effect on most chemical reactions

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Major Factors Influencing Chemical Transformation

• Soil Water Content
• Needed for microbial growth
• Affects bioavailability
• May limit oxygen content
• Needed for hydrolysis
• May affect soil-water interface pH
• Affects chemical availability

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Major Factors Influencing Chemical Transformation

• Acclimation
• Only affects Bio-transformations
• Possible time lag in degradation while some
  enzymes are induced.

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Major Factors Influencing Chemical Transformation

• Light
• Only affects non-biological transformation
• Some chemicals have a reaction activation energy
  level that must be satisfied.

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Transformation and Degradation Processes

• Simplest Relationship is Zero-Order
• Few chemicals fit this model

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Transformation and Degradation Processes

• Usually assumed to follow a first-order linear
  function
• This leads to an exponential decay function for
  the concentration

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Transformation and Degradation Processes

• K is the Degradation Coefficient
• K is related to the Half-Life of the chemical in
  the environment (TH) where C/ C0 0.5
• The Half-Life is the time required for the
  concentration of the chemical to become half of
  the initial value. Usually expressed in days.

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Transformation and Degradation Processes
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Transformation and Degradation ProcessesEXAMPLE

• Metolachlor (Dual) TH90 days
• Initial Concentration 1.5 kg/ha
• Estimate the concentration at 120 days.

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Transformation and Degradation Processes EXAMPLE

• TH90 days Co 1.5 kg/ ha
• Estimate the concentration at 120 days.
• Alternate Approximate Solution
• After 90 Days C 0.5x1.5 0.75 kg/ ha
• After 180 days C 0.5x0.75 0.375
• After 120 days 0.75 gt C gt 0.375 and closer to
  0.75. (approx. 0.6)

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Transformation and Degradation Processes

• Consecutive First Order
• The product of the degradation of compound A is
  Compound B.
• KA Decay Rate for Compound A
• KB Decay Rate for Compound B

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Transformation and Degradation Processes

• Numerical Solution to the Consecutive First-Order
  Degradation System

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Transformation and Degradation Processes

• Second-Order Degradation Process
• Not Commonly Used

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Photochemical Degradation
Light energy in the visible-UV range adds
activation energy which starts the breakdown.
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Photochemical Degradation

• k1 is the rate at temperature T1
• k2 is the rate at temperature T2
• R is the Universal Gas Constant
• Ea is the energy of activation
• T is temperature in degrees absolute

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BIOTRANSFORMATION PROCESSES

• BIODEGRADATION
• The chemical serves as a substrate for growth
• COMETABOLISM
• The chemical is transformed by metabolic
  reactions but does not serve as an energy source
  for the organism

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BIOTRANSFORMATION PROCESSES

• POLYMERIZATION OR CONJUGATION
• The molecules are linked together with other
  chemicals
• ACCUMULATION
• The chemical is incorporated into the organism.

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BIOTRANSFORMATION PROCESSES

• SECONDARY EFFECTS OF MICROBIAL ACTIVITY
• The chemical is transformed because of changes in
  the pH, redox conditions, reactive products, etc.
  in the environment brought about by the
  microorganisms.

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BIOTRANSFORMATION PROCESSES

• The actual processes involved in
  bio-transformation include the chemical processes
  of OXIDATION, REDUCTION, AND HYDROLYSIS
• The reactions generally result in metabolites
  which are more water soluble and, in most cases
  less toxic

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BIOTRANSFORMATION PROCESSES

• Rates of biotransformation are influenced by
  chemical properties
• STRUCTURE Some molecules have structure which
  makes it difficult for microbes to attack the
  chemical bond which they need
• SOLUBILITY Low solubility chemicals are hard for
  microbes to degrade.

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BIOTRANSFORMATION PROCESSES

• SORPTION Chemicals which are strongly sorbed,
  particularly absorbed into the soil particles,
  are not easily transformed by microbes.

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Aerobic Conditions
Alachlor remaining
Time in Days
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Anaerobic Conditions
Alachlor remaining
Time in Days
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Pothuluri, et al. 1990 J. Env. Qual. 19(3)525-530
Aerobic Conditions
Alachlor remaining
Time in Days
34
Pothuluri, et al. 1990 J. Env. Qual. 19(3)525-530
Anaerobic Conditions
Alachlor remaining
Time in Days
35
Pothuluri, et al. 1990 J. Env. Qual. 19(3)525-530
Aerobic Conditions
Alachlor remaining
Time in Days
36
Pothuluri, et al. 1990 J. Env. Qual. 19(3)525-530
Anaerobic Conditions
Alachlor remaining
Time in Days