Which of the following would indicate the greatest health hazard?

• A. 0.18 mg/L Chromium
• B. 0.01 mg/L Chromium
• C. 0.30 mg/L Copper
• D. 0.50 mg/L Lead

Answer: (A)

Health hazard in drinking water depends on how toxic a contaminant is and how much of it is present. Chromium is particularly concerning because, in its hexavalent form, it is highly toxic and carcinogenic. A chromium concentration of 0.18 mg/L signals a significant health risk due to the potential presence of Cr(VI), making it more hazardous than the other options at their given levels. The other values involve chromium at a much lower level (0.01 mg/L), copper well below common limits (0.30 mg/L), and lead at 0.50 mg/L—which is indeed dangerous, but in this context chromium’s form and concentration indicate the greatest health hazard.