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Random Walk Contaminant Spread

Random Walk Contaminant Spread. By Parrish Myers. DSES-6620 Simulation Modeling and Analysis Spring 2002. Median Lethal-Dose Acute Toxicity. Procedure Modeled after EPA SOP #2024 Data Obtained from EPA. Organism: Delphia Magna small freshwater crustacean Contaminant: Methyl Parathion

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Random Walk Contaminant Spread

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  1. Random Walk Contaminant Spread By Parrish Myers DSES-6620 Simulation Modeling and Analysis Spring 2002

  2. Median Lethal-Dose Acute Toxicity • Procedure Modeled after EPA SOP #2024 • Data Obtained from EPA • Organism: Delphia Magna • small freshwater crustacean • Contaminant: Methyl Parathion • insecticideLC50 = 0.14 ppb • EC50 = 0.09 – 0.2 ppb

  3. Simulation Assumptions • 2d • Contaminant spread: random walk of constant step size and not drift • The contaminant starts at the center of the system (0,0) • The contaminant is assumed discrete, containing N groups of molecules • Exits for molecule groups: • wander beyond system boundary • collision with an organism • Stochastic susceptibility for organisms • The organisms are stationary

  4. State Variables Modifiable • Number of Molecule Groups • Number of Organisms • Size of System System • System Time • Number of Dead Organisms • Number of Remaining Contaminant Molecule Groups • Radius of Contaminant

  5. RWCS System Area Organism Contaminant Simulation Controls Amount of Contaminant Number of Organisms Size of System State Variables State of Simulation

  6. Simulation Procedure • Keep system size at 50.0 and the number of organisms at 10 • Start with an amount of contaminant small enough to have minimal effect • Record the number of dead organisms at: • 1-Hour, 24-Hours, and 48-Hours • Increase the amount of contaminant and repeat step 3. • When organism mortality becomes 80%-90% STOP! • Tally data and find LD50.

  7. Simulation Results

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