a) Lab analysis of water from a lake showed it contains 0.25 mg/L cyanide, 0.19 mg/L nickel2+ and 12.2 mg/L chromium 3+. Provided the reference dose value for cyanide, nickel and chromium are 0.02mg/kg-day, 0.02 mg/kg-day and 1.0 mg/kg-day, respectively. Assess whether consumption of this water is safe or not. Assume adult is 70kg and drink 2L/day. [5 marks] b) Determine the maximal number excess lifetime cancer cases expected for a population of 1 million from benzene via inhalation (from multiple sources including second-hand smoke, gasoline vapor, etc.). Assume that the chemical benzene, a known carcinogen, found in air at a constant concentration of 1ug/m' with potency factor 0.029 (mg/kg-day)?. Calculate the risk to this benzene for an average adult who inhales 20 m' air per day with 50% absorption for a lifetime. [5 marks]