Water standards set that the maximum contaminant levels (MCL) of mercury and cadmium in water are 0.002 mg/kg and 0.005 mg/kg, respectively. What are these values in parts per million (ppm) and indicate the maximum level of each contaminant (in mg) in 200 g of water?

• A. Mercury: 0.02 ppm, 4×10^–4 mg
  Cadmium: 0.005 ppm, 1×10^–3 mg
• B. Mercury: 0.002 ppm, 4×10^–4 mg
  Cadmium: 0.005 ppm, 1×10^–3 mg
• C. Mercury: 0.02 ppm, 0.4 mg
  Cadmium: 0.05 ppm, 1 mg
• D. Mercury: 0.002 ppm, 0.4 mg
  Cadmium: 0.05 ppm, 1 mg

Answer: (B)