Persistent Organic Pollutants

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The Turtle by Ogden Nash   The turtle lives
'twixt plated decks Which practically conceal
its sex. I think it clever of the turtle In
such a fix to be so fertile.
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Uptake accumation of POPs in living organisms

• Some terms describing the uptake of chemicals by
  organisms

Bioconcentration the increase in concentration
of a chemical in an organism compared to that in
the medium in which it lives
Bioconcentration factor (BCF) the ratio of the
concentration of a chemical in an organism
compared to that in the ambient medium
Bioaccumulation the processes by which an
organism takes up and retains a contaminant
through multiple exposure routes
Biomagnification a series of processes that
results in a chemical becoming increasely
concentrated at successively higher trophic
levels of a food chain or food web.
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Examples of bioconcentration and
biomagnification of DDT in the Lake Kariba
ecosystem
The extent of bioconcentration is quantified with
the BCF
E.g. DDT in mussels of the Firth of Clyde (1989)
300 µg kg-1 DDT in sea water 1 ng L-1 BCF
30010-6 g (1 kg mussels) 110-9 g (1
kg water) 300 000
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Partitioning of organic solutes between water and
soil or sediment

• In the aqueous environment, molecules such as
  POPs distribute themselves between water and
  solids, whether sediment and suspended solids.

For organic solutes at low concentrations, a
reasonable description of this partitioning is
given by a modified Freundlich relation Cs
KdCaq where Kd is the distribution coefficient
(Kd Cs / Caq)
Kd depends on (a) solute, (b) chemical
physical nature of the solid phase, (c)
environmental factors such as temperature and
ionic strength
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Partitioning of organic solutes between water and
soil or sediment
Since Kd depends on multiple, partially defined
variables, its actual value is difficult to
predict with any accuracy
Other distribution coefficients are therefore
commonly used to quantify how much particulate
surfaces will take up an organic solute
KOW the octanol-water partition coefficient
KOM the organic matter-water partition
coefficient
These partition coefficients can be related to
the distribution coefficient, Kd
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Sorption of organic species by solids in the
environment
The distribution of organic species between the
solid phase and water depends on some properties
of the solid
1) Mineral components
Exposed surfaces may contain functional groups
(such as hydroxyl groups from hydrous oxides and
clays) that may form specific interactions with
organic solutes Interactions include
dipole-dipole and hydrogen bonding Interactions
with organic solutes are usually weak because
adsorption necessarily displaces water molecules
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Sorption of organic species by solids in the
environment
2) Organic components
Organic solutes generally interact more strongly
with organic matter on solids These include humic
material from plant and microbial sources Organic
matter has some polar functional groups but also
hydrocarbon regions Organic solutes have little
competition with water for these hydrocarbon
sites Organic solutes can adsorb onto or absorb
into these organic areas hence the term sorption
Even small concentrations of organic components
on solids typically dominate partitioning of
organic solutes from water
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Sorption of organic species by solids in the
environment
The equilibrium concentration of sorbed solutes,
Cs, is then Cs fOM COM fMM
CMM where fOM and fMM are the fractions of
organic matter and mineral matter in the soil or
sediment, and COM and CMM are the concentrations
of the organic solute in each phase
Since organic solutes interact weakly with
mineral surfaces in sediment, CMM is usually
small and we can write
Cs fOM COM
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Octanol-water partition coefficient
n-Octanol serves as a useful model for humic-like
substances - it is an amphiphilic solvent with
both hydrophilic and hydrophobic constituents -
it has a similar ability to associate with polar
and nonpolar compounds
The octanol-water partition coefficient, KOW,
therefore provides a convenient measure of the
extent to which a hydrophobic solute will
dissolve in water or be sorbed by organic matter.
KOW CO/Caq
where CO is the equilibrium molar solubility of
the solute in n-octanol and Caq is the
corresponding solubility in water
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Octanol-water partition coefficient
Large values of KOW indicate that the solute is
strongly associated with the organic matter
small KOW values that the solute favours the
aqueous phase
How does KOW relate to bioconcentration?
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KOW and BCF
As we would expect, there is a correlation
between KOW and BCF for a range of persistent
organic pollutants
KOW can therefore be used to predict the BCF of
a particular solute
Bioconcentration of a molecule becomes a concern
for BCF values above about 10 000
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The Ant by Ogden Nash   The ant has made
himself illustriousThrough constant industry
industrious.So what?Would you be calm and
placidIf you were full of formic acid?