Essential Questions: Transformation

Question 1

What are the main transformation processes for organic priority pollutants?

Answer 1

• Chemical transformation
• Photochemical transformation
• Biologically mediated transformation
• Degradation in WWTP
• Biodegradation kinetics testing in mixtures at environmentally low concentrations
• Biotransformation in larger organisms
• Parent compounds and metabolites

Transformation processes take place in both the environment and within the organism. Bio-processes usually take place aerobically (most dominant) rather than anaerobically.

Question 2

Can you explain the difference between Phase 1 and Phase 2 reactions within biotransformation?

Answer 2

Phase 1 reactions include oxidation, reduction, and hydrolysis => introduction of functional group (-OH, -COOH, -NH2, -SH). There are simple reactions, where typically a more polar group is introduced.

Phase 2 reactions include conjugation => conjugation with endogenous water soluble moiety (glutathione, sulfate, carbohydrates, …). The moiety (“a small fragment”) is something that the organism invests in, which evolutionarily speaking is something it does to get rid of things, i.e. to excrete the compounds.

Question 3

Do Phase 2 reactions increase or decrease excretion from the body?

Answer 3

Increase.

Question 4

What is bioactivation? Can you give an example?

Answer 4

In some cases, biotransformation makes things worse by transformation a toxic chemical into an even more toxic one. This is called bioactivation.
Example: epoxidation of benzo[a]pyrene (product: epoxide).

Question 5

Does biotransformation lead to higher or lower bioaccumulation?

Answer 5

Lower. That is, it leads to lower concentration of the parent compound.

Question 6

Does biotransformation lead to higher or lower toxicity?

Answer 6

Lower, but depends. In some cases, the product can be as toxic or even more toxic than the parent compound.

Question 7

Which removal processes in WWTP are transformation and which are distribution processes?

Answer 7

Stripping and sorption are distribution processes.

Biodegradation is transformation.

Question 8

Which agent can be used for chemical oxidation of pollutants?

Answer 8

Ozone (note: Chlorination is more of a sterilization).