Q1. Given that daily cancer death rate (CDR) is calculated using (Equation 1):
CDR= (Carcinogenicity potency of radon)×(Radonconcentration)×(Exposuretime)……….. (1)
If radon concentration in a village varies between 0.28 pCi/L and 2.72 pCi/L values, calculate range of CDR values for residents exposed to it for 20 hours/day? (Radon cancer potency = 10-8 Cancer deaths per hour of exposure at1 pCi/L).(10points)
CDR= (Carcinogenicity potency of radon)×(Radonconcentration)×(Exposuretime)
Q2. What do you understand by threshold response and non-threshold response? Explain this concept taking chemicals as example contaminants and by plotting on the risk vs dose plane? (10 points for write up + 5 points forplot)
Q3. Suppose a 50-kg individual drinks 2 L day of chloroform and 0.1 mg L1 phenol.What is the hazard index? Is there cause for concern? (10 points)
Q4. Estimate the cancer risk for 70-kg individual consuming 1.5 liters of water containing trichloroethylene (TCE) per day for 70 days. (10 points)
Q5. Using the U.S. Environmental Protection Agency IRIS database (www.epa.gov/iris), find the critical effect, uncertainty factor, and NOAEL, LOAEL, and RfD for mercury, chromium, and chloroform. In drinking water, which one would be the most toxic? (10 points)
Q6. A small stream with a flow rate of 0.1m3/sec empties into a river that has a flow rate of 2m3/sec. The stream is affected by mining operations and is contaminated with arsenic at a concentration of 50mg/L. The river is not affected by mining and has arsenic concentration of 0.03mg/L upstream from the small stream. What is the arsenic concentration in the river downstream from the stream? Provide the conceptual model to support your solution.
(15 points for calculation + 5 points for conceptual model)
Q7. Consider the electroplating facility that discharges to a river liquid wastes containing chromium. The effluent flow rate is 0.05m3/sec and the river flow rate is 5m3/s. if the concentration of chromium in the river is not allowed to exceed 100microgram/L, what is the maximum allowable concentration of chromium in the effluent?
(10 points for calculation + 5 points for conceptual model)
Q9. Consider a contaminant having a concentration C0= 10mg at t=0 which undergoes firstorder decay with k=0.4min-1. Generate a table of C as a function of time upto a maximum time of 10 minutes in step of 2 min. Plot this C v/s TIME on a sheet of paper (preferably graph paper) with proper labels and titles. Sample graph sheet is provided below, you can paste your excel plot directlytoo.(15 points for calculation + 5 points forplot)
Q10. If 3.0 g of substance AA decomposes for 36 minutes the mass of unreacted A remaining is found to be 0.375 g. What is the half life of this reaction if it follows first-order kinetics? (5 points)
Q11. A tank aboard a barge traveling along the Chicago Ship Canal suddenly collapses, releasing its benzene content (C6H6, density = 0.879 g/cm3), of which 100 liters find their way quickly to the water. The rest of the benzene remains contained on the barge. Assuming rapid mixing across the canal section (8.07 m deep and 48.8 m wide) and estimating the turbulent diffusion coefficient at 3.0 m2/s. The canal has the Peclet number << 1, which means that the flow rate of canal water is negligible and Diffusion is the only force acting in spreading thecontaminant.
i) what are the concentrations of benzene 2, 6, 12 and 24 hours after the accident, at the site of the spill and 300 m away? Fill your answers for 5 blanks in thetablebelow. (15pts)
Conc. at spill (mg/L)
Conc at 300m(mg/L)
ii) calculate the exact time at which the concentration reaches its maximum (answer in hr:min) (5pts)
iii) what that maximum concentration is? (answerinmg/L) (5pts)
iv) Comment on the concentration profile at 300m. Is it dropping continuously or increasing or both,andwhy? (5pts)
Important conversions: gms/cm3 = kg/L; 1Kg = 1000 mg
HINT: – Mass = density * Volume; so mass of spill is = 0.879 g/cm3* 100L = 0.879kg/L*100L
Equations to be used when advection is negligible –