Industrial mercury pollution sources: Which industry has historically been a significant source of mercury discharge to air and water, especially where the mercury cell process was used?

Introduction / Context:
Mercury is a potent neurotoxin with well-documented environmental and health impacts. Identifying principal industrial sources is key to regulatory control and remediation strategies.

Given Data / Assumptions:

• Focus on historical and legacy discharges rather than modern closed-loop plants.
• Mercury cell chlor-alkali processes used mercury as a cathode in chlorine and caustic soda production.
• Other listed industries may emit different pollutants but are not classic mercury sources.

Concept / Approach:
In the mercury cell process, losses of elemental mercury could occur via fugitive emissions, brine sludge, and wastewater, leading to contamination of local environments. Many jurisdictions have phased out or retrofitted such plants, but the historical association remains strong.

Step-by-Step Solution:
Match pollutant to process: mercury → mercury cell chlor-alkali.Eliminate distractors: tanneries (chromium), nitric acid (NOx), phosphoric acid (fluoride, phosphogypsum), beverages (minimal pollutants).Select “Chlor-alkali industry.”

Verification / Alternative check:
Environmental case studies of riverine mercury hotspots often trace back to legacy chlor-alkali plants using mercury technology.

Why Other Options Are Wrong:
Tanneries: concerns include chromium and sulfide, not mercury.Beverage plants: sanitary wastewater, not heavy metals.Phosphoric acid: fluoride and radionuclide issues dominate.Nitric acid: NOx emissions, not mercury.

Common Pitfalls:
Confusing mercury with chromium or lead sources; overlooking the specific electrochemical process that used mercury metal.

Final Answer:
Chlor-alkali industry