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

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)

TIME (Min.)

Concentration (mg)








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.

Answer following –

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)

2 hours

0.428 mg/L


6 hours



12 hours

0.175 mg/L


24 hours



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

= 87.9KG

Equations to be used when advection is negligible –

C(x,t) =