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Generic model for population Generic model for population affected - - PowerPoint PPT Presentation
Generic model for population Generic model for population affected - - PowerPoint PPT Presentation
Generic model for population Generic model for population affected by chronic irradiation affected by chronic irradiation A.I. Kryshev Kryshev, T.G. , T.G. Sazykina Sazykina A.I. Research & Production Association Research &
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The following umbrella endpoints were taken into consideration: morbidity, reproduction, decrease of the population size
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The effects caused by chronic irradiation in population are considered to be a result of superposition of three major processes – creation of damage by radiation, recovery of damage by means of repairing mechanisms, natural growth of population
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‘Repairing system’ is considered as a complex entity (a kind of “black box”), which repairs damage caused by ionizing radiation and other stressors.
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Let us consider an isolated generic population, living under ideal conditions (no predators, no limitation by food,
- ptimal temperature and other
environmental factors), which is exposed to chronic ionizing radiation with a dose rate p (mGy/day)
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We assume, that organisms composing the exposed population may be in one of the following states: undamaged, reversibly damaged, lethally damaged
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Reversible damages are recovered by the repairing mechanisms, the repairing pool is spent for the repairing processes. Effect on morbidity of organisms in the population depends on decrease
- f the repairing pool (in % from its
initial value). The ionizing radiation also cause a direct damage to the repairing pool itself.
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Reproduction system increases number of normal organisms in the population, but itself is affected by the ionizing radiation
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A system of differential equations describing the effects of chronic radiation exposure on fish population can be written as:
max max max max max max max
) ( ; ) ( ; ) ( ; ) ( ) ( ) ( ) ( ) ( F F R R y x x F F F x x F F p dt dF R p yR R R R dt dR yR y px dt dy F x x yR px dt dx
f f r r r
= = = = − ⋅ ⋅ + − ⋅ ⋅ − ⋅ ⋅ − = ⋅ ⋅ − ⋅ − − ⋅ ⋅ = − − = ⋅ − ⋅ + + − = µ µ α α κ µ κ ε α µ κ α
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Effect of the chronic radiation exposure on the survival was estimated using the ratio X/Xmax. Effects on reproduction were described by the ratio F/Fmax. Effects on morbidity were described by the ratio R/Rmax.
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0,2 0,4 0,6 0,8 1 20 40 60 80 100 Dose rate, mGy/day Survival of population, %
Decrease of population size with the increase of dose rate
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0,2 0,4 0,6 0,8 1 5 10 15 20 25 Dose rate, mGy/day Repairing pool, %
Decrease of repairing capacity with the increase of dose rate
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Dose rate – effect curve in general form:
α
) / ( 1 1 ) (
50
P P P X + =
In our model: P50=32.5 mGy/day; α=5.5
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0,2 0,4 0,6 0,8 1 1,2 20 40 60 80 100 Dose rate, mGy/day Survival decrease, % Empiric formula Model calculation
Dose-effect curves obtained from the general empiric formula and from the dynamic population model
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