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Ecotoxicological Models

Ecotoxicological Models. Sven Erik Jørgensen DFU, Environmental CHEMISTRY University Park 2, 2100 Copenhagen Ø, Denmark sej@dfuni.dk. Assessment factor – safety factor. 1000 no long term effect is known and at least one short term effect is known 100 one long term effect is known

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Ecotoxicological Models

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  1. Ecotoxicological Models Sven Erik Jørgensen DFU, Environmental CHEMISTRY University Park 2, 2100 Copenhagen Ø, Denmark sej@dfuni.dk

  2. Assessment factor – safety factor • 1000 no long term effect is known and at least one short term effect is known • 100 one long term effect is known • 50 two long term effects are known • 10 three long term effects are known Field observations, microcosmos observations: evaluated from case to case.

  3. Characteristics of ecotoxicological models • 1.Many parameters are needed to cover all toxic substances • 2. High safety margin (RQ uses high assessment factors) • 3. Effect component • 4. Often simple due to 1) and 2)

  4. Procedure for development of ecotoxicological models • Obtain knowledge about focal processes • Get parameters from literature • Estimate unknown and a few known parameters • Compare results from 2 and 3 and explain discrepancies • Use sensitivity analyses for processes and parameters to simplify

  5. Three types of fate models: • Model the fate of a chemical compounds in a region. Often denoted fugacity model. This type of models has a high uncertainty. They are used to select the most environmentally friendly chemical • Model of a specific case of pollution by a toxic substance • Model that is calibrated and validated by a specific case and thereafter used more generally for ERA , often in a worse case situation

  6. Five types of effect models: • Organisms level • Population dynamic model with effect on mortality and growth etc. • Ecosystem model with effects of the presence of toxic substances on several parameters • Landscape model – several linked ecosystem models with effect on the parameters • Global model: the global dissemination of a toxic substance with effects on the global processes for instance the global cycles

  7. Chemostate case: • dC/ dt = (Q*Cin- Q*C)/V- k*C • Steady state C ( Q+ kV) = Q Cin or • C = Q Cin / (Q + kV) • Next slide shows C = f(time) when Cinitial = 0

  8. An organisms as the box: • dTx / dt = (daily) input - kTx • At steady state: • dTx /dt = 0 • kTx = input or Tx = input / k

  9. The concentration of a toxic substance considering growth • dW/dt = aWb - rWd b≈ 0.67; d≈ 0.75 • Uptake from water= BCF*Cw*dW/dt • Uptake from food= aWb*Cf*eff • Excretion= exc*Corg • dTx/dt = BCF*Cw*dW/dt + aWb*Cf*eff • - exc*Corg • Corg = Tx/W = f (time)

  10. Cr contamination in Faaborg Fjord

  11. MODEL DESCRIPTIONImportant Processes: • Precipitation of Cr(III) (OH)3 • Transport to the open sea by mainly tide • Bioaccumulation sediment -> blue mussels

  12. The following second order differential equation is valid: • dC / dt = D*C(X)´´ – QC(X)´ – K (C – Co) / h • Where • C is the chromium concentration (mg/l) • X is the distance from the discharge point (m) • Q is the waste water flow cubicmeter / 24h • K is the settling rate (m /24h) • Co is the soluble chromium concentration (mg/l) • h is the water depth (m)

  13. Solution of D*C(X)´´ = k (C – Co) / hY = K(C – Co) = (Cu/F)( hK/D) exp( -K /hD) X + IK*IK Cu is the total discharge. The annual total discharge is 22 400 kg

  14. We can find the settling rate K • Y mg Cr / m^2 day = K (C – Co), • Y is known and C- Co is known for all the station. Co is 0.2 mg/l • Is the found K-value reasonable?

  15. Process equations: • ads= tsw*ac – tss • dsp= tss/ac - tsw • dcp= dr*tsw*1.05(TEM- 20) • adm=msw*ad – mss • dsm=mss/ad – msw • dcm=dm*mss*1.05(TEM- 20) • drt=tsw*dra • drm=msw*dra • eva=eps+epp • dra= if wrz>= wf*400 then (0.1*(wrz-400*wf) else (sl*(400*wf- • wrz)/(ws-wp) • epp=( fa*la*0.931*dl*RAD) /((dl + 66.7)*2.47) • eps= 0.7*dl*RAD*fa*exp(-0.4*la) / ((dl + 66.7)*2.47) • put = tpl*eg*RAD*tsw / (rz*4.1*(tsw+msw) • pum = tpl*eg*RAD*msw / (rz*4.1*(tsw+msw)

  16. Additional equations: • dl= 3+ + 3*TEM +0.17*TEM2 • fa= if wrz>= wf*400 then (0.1*(wrz-400wf) else ((400*wf-wrz)/(400wf) • la= lm/(1+exp(1-0.01*TIME) (TIME is the time in days, which is used as the time unit). Notice it should be possible to select between the application of calculations for la by the shown equations or to give information about la as function of time. Notice that the time applicable for the shown equation is the growing season and if there are no plants it is a matter of setting lm = 0. • tpl = (tsw + msw)* (pw + 1.22*pl*Kow^b)* ( dp/dw) • wf=0.46*cl + 0.305*si+0.25*oc • wp= 0.33*cl+0.12*si+1.6*oc • wxs=0.69*cl+0.55*si+4.28*oc

  17. Parameters: • Parameter Symbol Unit Range Value • Adsorption coefficient ac kg/l 0-10000 128 • Adsorption coefficient • for metabolites ad kg/l 0-10000 128 • Decomposition rate dr 1/24h 0-100 0.35 • Decomposition rate • For metabolites dm 1/24h 0-100 0.20 • Water cont. in plants pw kg/kg 0-1.00 0.3 (plant dependent) • Lipid cont. in plants pl kg/kg 0-100 0.1 (plant dependent) • Octanol-water coeff. Kow - 0-10^6 1000*) • Eff. plant growth eg kg/ MJ 0.001-0.1 0.025 • Density plants dp kg/l 0.9-1.5 1.000 • Density water dw kg/l 0.95-1.05 0.998 (at 20oC) • Exponent b - 0.5-1.0 0.80 (plant dependent) • Root zone depth rz m 0.2-1.0 0.5

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