Problem $4\mathrm{.}17($modified$),$ Masters and Ela, Introduction to Environmental Engineering and Science, $3$rd Ed$.$:

You have just taken a job at a metal plating plant, and some of the metals you work with contain arsenic as an impurity. The heated metals give off arsenic vapors, which create an average concentration of arsenic of $4\mathrm{.}5{10}^{-5}m\frac{g}{m^3}$ in the air in the workplace.

a$.$ What is your increased risk of cancer if you continue to work in this job for your entire career?

b$.$ There are about $225,000$ workers in the United States in metal casting plants similar to the one in which you work. How many worker deaths above the background cancer rate $(21\%$ of deaths$)$ would be expected due to their occupation?

c$.$ Of the $225,000$ workers in metal casting plants, how many would be expected to die of cancer in total?

d$.$ Suppose your workplace air also contains mercury in the air with an average concentration of $1\mathrm{.}8{10}^{-4}m\frac{g}{m^3}.$ Would the combined hazard index for arsenic and mercury suggest that this a safe level of exposure?