Metals as water/air pollutants There are several metals classed as priority pollutants for health and environmental reasons. Which metal listed below is generally not treated as a toxic priority pollutant in typical regulations?

Introduction / Context:
Environmental regulations often identify certain metals as toxic pollutants because they bioaccumulate, persist, or cause acute/chronic toxicity. Understanding which metals are prioritised helps engineers focus monitoring and treatment on substances of greatest concern.

Given Data / Assumptions:

• “Pollutant metals” refers to toxic priority metals commonly cited in water/air regulations.
• We compare toxicity, persistence, and regulatory emphasis.
• We select the one not typically listed as a priority toxic metal.

Concept / Approach:
Mercury, arsenic, lead, and cadmium are classic toxic metals with strict limits due to neurotoxicity, carcinogenicity, or kidney damage. Aluminium, while abundant and regulated for aesthetic/operational issues in water treatment, is not usually grouped with the “toxic priority metals” like Hg, Pb, Cd, As. Hence, aluminium is the correct choice here.

Step-by-Step Solution:

Verification / Alternative check:
Regulatory frameworks consistently treat Hg, Pb, Cd, and As as hazardous with very low permissible limits, whereas aluminium often has secondary (aesthetic/operational) guideline values in drinking water.

Why Other Options Are Wrong:

• Mercury, Arsenic, Lead, Cadmium: All are well-known toxic priority pollutants with stringent controls.

Common Pitfalls:
Confusing “commonly occurring” with “non-pollutant”; abundant presence does not imply low concern, but in aluminium’s case, regulatory focus is typically different from heavy toxic metals.

Final Answer:
Aluminium