Which of the following is listed as a priority pollutant?

• A. Nitrates
• B. Cadmium, chromium, copper, lead, nickel, zinc, arsenic, cyanide, silver, mercury
• C. Phosphates
• D. Chloride

Answer: (B)

The question checks whether you know which contaminants are designated as priority pollutants under the Clean Water Act. These are the substances for which the EPA commonly sets stringent effluent limits and requires monitoring in NPDES permits. The group listed—cadmium, chromium, copper, lead, nickel, zinc, arsenic, cyanide, silver, and mercury—is exactly the set of metals and related toxins traditionally identified as priority pollutants. They are emphasized because even at low concentrations they can be highly toxic to aquatic life and humans.

Nitrates and phosphates are nutrients and common pollutants, but they aren’t part of the priority pollutant list. Chloride is a salt that’s regulated in various ways, but it isn’t one of the priority pollutants. So the option that lists the metals, arsenic, cyanide, silver, and mercury aligns with the official priority pollutants.