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Ecotoxicology Transport of contaminants. The transport of contaminants in the atmosphere takes place: Globally Large-scale:> 1000 km Meso-scale:10 - 1000.

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Presentation on theme: "Ecotoxicology Transport of contaminants. The transport of contaminants in the atmosphere takes place: Globally Large-scale:> 1000 km Meso-scale:10 - 1000."— Presentation transcript:

1 Ecotoxicology Transport of contaminants

2 The transport of contaminants in the atmosphere takes place: Globally Large-scale:> 1000 km Meso-scale: km Micro-scale:< 10 km

3

4 The dispersal of chemicals is a function of their atmospheric lifetime Boundary layer →tropopause: > 5 days Whole tropospheric hemisphere: > 1 monthGlobal troposphere: > 2 yearsTroposphere → Stratosphere: > 10 years Examples NO 2 ( ~ 1 day) - only small exchange to the free tropopause Aerosol from Chernobyl ( ~ 1 month) - spreading to the whole Northern hemisphere Metan (~ 4 years) - mixing between both hemispheres Chlorfluorocarbon (CFC) (~ 100 years) - transport to the stratosphere

5 The global transport EquatorSouthNorth Hadley circulation

6 Typical forms and sizes of trace metals in aquatic systems Metal species Free metal ions Inorganic ion pairs Inorg. complexes Low mol. Wt. or- ganic complexes High molecular org. complexes Metals adsorbed onto inorganic colloids Metals adsorbed Into living cells Metals adsorbed Onto or incorpora- ted into mineral soils and precipita- tes Ex.Mn 2+ Cd 2+ NiCl + HgCl 4 2- Pb-humatesCo-MnO 2 Pb-Fe(OH) 3 Cu-clays PbCO 3(5) Soluble Colloidal Particulate Size nm nm nm nm

7 Concentration of Cr µg / l Average flow (m 3 s -1 ) DissolvedSuspended Nitrate Phosphor Concentration of chromium in the River Thames as a function of flow rate

8 Thermic boundary layer Wind + Coriolis force

9 Atmosphere-land surface exchange Dry deposition:particles and gases Wet deposition:Rainfall and fog Flux to surface = Vg atmospheric concentration at 1 m Vg = deposition velocity Vg = = cba rrr ++== 1 R - r a : aerodynamic resistance to within 1-2 mm of the surface - r b : the resistance of the individual roughness elements in the boundary layer (ca 1 mm) - r c : the resistance of the surface itself to take-up of the gas Flux to surface Atmospheric concentration at 1 m Resistance to deposition

10 Deposition velocity of particles depends on their size µm: Vg high (high diffusivity – like gasses) µm: Vg small (atmospheric lifetime: 7-30 days) µm: Vg high (heavy)

11 Washout from the atmosphere  W(drops) = Air:microgram/m 3 (1 m 3 air weighs 1,2 kg) Rain:mg/l Washout factor W Concentration in rain (mg/kg) Concentration in in air (mg/kg)

12 The flux between air and sea Henry’s law: H=K·α·P H = solubility of gas K = constant α = the gas’ coefficient of absorption P = partial pressure of the gas C air · H -1 = C water : equilibrium (H -1 Henry’s law constant) C air · H -1 > C water : net transport air  water C air · H -1 < C water : net transport water  air If:ΔC = C air · H -1 – Cwater The transport of material is: F = K (T)W · ΔC (K (T)W : ”transfer velocity”) aWWT HkkK 111 )(   where k w and k a are the individual transfer velocities for gasses in water and air

13 Air – sea transfer velocity for CO 2 Points: Experimental data Line: Calculated

14 Water – sediment exchange Dissolved Suspended Sediment Water - suspended K d = Water – sediment -less efficient due to limited extent of contact Suspended – sediment (sedimentation) most important for the removal of contaminants from the water Sedimentation rates are expressed as the rate of bottom increase -oceans: mm / 1000 years -lakes, estuaries: cm / year Distribution coefficient Concentration in solid phase material (mg/kg) Concentration in dissolved phase (mg/kg)

15 SedimentationExchange of pore water Physical mixing of sediment Upward flow of pore water Hydrostatic pressure Vand – sediment fluxe )( 0 SSz CUUC dz dC DPFfluxNet   P: Porosity (volume fraction occupied by water) D: Diffusion coefficient C: Concentration in solution C S : concentration in solids U: rate of pore water advection U S : Sedimentation rate z: Vertical distance

16 Redox-active compounds Example: Ion and Manganese Fe 2 O 3 MnO 2 Fe +++  Fe ++ Mn ++++  Mn ++ Oxic Anoxic Bound to sediment Dissolved in pore water Oxic zone Anoxic zone

17 Atmospheric CO 2 -concentration measured in Hawaii ( ) Lead concentration in ice core from Greenland


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