I am studying for the FE exam and have come across a question regarding calculating cancer risk. I'm fairly certain that the answer provided has typos, but I'm not 100% sure. Here is the question:

A carcinogen is in drinking water at a concentration of 0.01 mg/L. The cancer risk of 30 years of adult (75 kg) exposure, given a cancer slope factor of 0.80 [mg/(kg*day)]^-1, is most nearly:

I understand that the chronic daily intake equation is CDI = [(Concentration)(Ingestion Rate)(Exposure Frequency)(Exposure Duration)]/[(Body Weight)(Averaging Time)]

Here are my issues with solution provided:

  1. The ingestion rate is 2.3 L/day. That wasn't given in the question, and the standard ingestion rate anyways given by the EPA is 2 L/day. How did they come up with this number? Is it likely just a typo?
  2. For "Averaging Time", they have multiplied 75*365...shouldn't it be 30*365 since the question states that it is 30 years of exposure??
  • $\begingroup$ For the Medical Sciences Stack? $\endgroup$
    – Solar Mike
    Commented May 11, 2019 at 19:08
  • $\begingroup$ Not sure, since this is an environmental engineering topic I figured I'd put it in the engineering stack. $\endgroup$
    – Ryan_C
    Commented May 11, 2019 at 19:09
  • $\begingroup$ I just took FE this year, chemical. If I remember right, I think averaging time for CDI is lifespan, not years of exposure. Did they give an average lifespan? $\endgroup$
    – Ohio ChemE
    Commented May 12, 2019 at 1:10

1 Answer 1


The 75 is the exposure duration (ED) in this scenario it is a carcinogen so the lifetime duration is used. enter image description here

  • $\begingroup$ A reference/citation for the information in the answer should be included. $\endgroup$
    – Fred
    Commented Oct 19, 2022 at 18:30

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