1 The Turtle by Ogden Nash 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.

2 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.

3 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 = 300×10 -6 g (1 kg mussels) 1×10 -9 g (1 kg water) =

4 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: C s = K d C aq where K d is the distribution coefficient (K d = C s / C aq ) K d depends on: (a) solute, (b) chemical & physical nature of the solid phase, (c) environmental factors such as temperature and ionic strength

5 Partitioning of organic solutes between water and soil or sediment Since K d 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: K OW – the octanol-water partition coefficient K OM – the organic matter-water partition coefficient These partition coefficients can be related to the distribution coefficient, K d

6 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

7 Sorption of organic species by solids in the environment 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 2) Organic components: Even small concentrations of organic components on solids typically dominate partitioning of organic solutes from water

8 Sorption of organic species by solids in the environment Since organic solutes interact weakly with mineral surfaces in sediment, C MM is usually small and we can write: The equilibrium concentration of sorbed solutes, C s, is then: C s = f OM × C OM + f MM × C MM where f OM and f MM are the fractions of organic matter and mineral matter in the soil or sediment, and C OM and C MM are the concentrations of the organic solute in each phase C s ≈ f OM × C OM

9 Octanol-water partition coefficient The octanol-water partition coefficient, K OW, therefore provides a convenient measure of the extent to which a hydrophobic solute will dissolve in water or be sorbed by organic matter. 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 K OW = C O /C aq where C O is the equilibrium molar solubility of the solute in n- octanol and C aq is the corresponding solubility in water

10 Octanol-water partition coefficient Large values of K OW indicate that the solute is strongly associated with the organic matter; small K OW values that the solute favours the aqueous phase How does K OW relate to bioconcentration?

11 K OW and BCF As we would expect, there is a correlation between K OW and BCF for a range of persistent organic pollutants: K OW can therefore be used to predict the BCF of a particular solute Bioconcentration of a molecule becomes a concern for BCF values above about

12 The Ant by Ogden Nash Ogden Nash The ant has made himself illustrious Through constant industry industrious. So what? Would you be calm and placid If you were full of formic acid?