Legacy Persistent Organic Pollutants

Question 1

What are POPs?

Answer 1

• POPs= persistent organic pollutants
• There are 12 initial pops, or legacy pops, that got on the Stockholm convention.
• These were pesticides, industrial chemicals and chemicals produced accidentially:
• They all contain the halogen chlor in the chemical structure.
• Examples:
  • Aldrin: insecticide
  • Endrin:
  • Chlordan: pesticide
  • DDT: used to combat malaria and tyfus
  • Dieldrien: pesticide
  • Heptachlor
  • Mirex: pesticide (insecticide-fireants). Also used as flame-retardant, in plastic and rubber.
  • HCB
  • PCBs: industrial chemicals. Used in electronics and in building materials. Used as sealants around windows as to keep the sealant soft.
  • Toxaphene: Pesticide
  • PCDDs: dioxins
  • PCDFs: similar to dioxins

Question 2

What are the physical-chemical properties of POPs?

Answer 2

• Common for all compounds: they contain the halogen chlor. Several of them are aromat-
ics/contain a benzene ring, others are cyclic. The molecular weigh is 200-500 g/mol.

• They are semi-volatile. That means that they partition back and forth. They have low water
solubility.

• Dissociation does not play a major role, as they are neutral substances.
• Kow: kow is usually on the very high end.
• Bioaccumulation: as logkow is high they have potential for being bioaccumulated.

• Degradation: low degradation of these chemicals, which highligts that these are rather persis-
tent chemicals.

• Toxicity: different from compound to compound, but there are some toxic issues.

Question 3

Explain POPs in relation to Transportation.

Answer 3

• POPs undergo longe-range transport due to primarily their Semi-volatile nature. (explain LRT)
• It is a criterium to be on the Stockholm convention then they have to undergo longe-range transport
  and be a PBT com.

Question 4

Explain POPs in relation to Distribution.

Answer 4

• Distribution is the most dominating process for legacy pop.

• They are both hydrophobic and semi-volatile i.e. that they can distribute in several media.

• Due to their persistent nature they had/have the time to distribute into the environment.
whereas we look at something as hydrocarbons in a e.g. oil-spill then one year later these
compounds are gone, most likely being degraded.

• Bioaccumulated in several organisms. Also see several studies show a biomagnification of the
compounds in higher trophic levels.

Question 5

Explain POPs in relation to transformation.

Answer 5

• PCBs can be anaerobically dechlorinated by organohalide respiring bacteria in sediments.
  • Low chlorine number, more water soluble and easier to cut out.
  • Some bacterial strains can degrade PCB congeners