Ecotoxicology Transport of contaminants

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

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

The global transport EquatorSouthNorth Hadley circulation

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

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

Thermic boundary layer Wind + Coriolis force

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

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)

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)

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

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

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)

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

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

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