Why is there a concern about copper smelting plants? The copper slag can cause the leaching of some heavy metals into the environment? They may release sulphur dioxide as a pollutant? [2021]

Why is there a concern about copper smelting plants?

They may release lethal quantities of carbon monoxide into the environment.
The copper slag can cause the leaching of some heavy metals into the environment.
They may release sulphur dioxide as a pollutant.

Smelting is the process of extracting a metal from its ore. Copper smelting plants do not significantly emit carbon monoxide; this gas is mainly associated with incomplete combustion.

Carbon monoxide is a colourless, odourless, tasteless and highly toxic gas that is slightly less dense than air. It is short–lived (stay only a few months) in the atmosphere. It is produced from the exhaust of internal combustion engines and the incomplete combustion of various other fuels. Iron smelting also produces carbon monoxide as a by-product. It forms when there is not enough oxygen to produce carbon dioxide (CO2).
In the presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide.
Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere. Other natural sources of CO include volcanoes, forest fires, and other combustion processes.

Copper, while an essential nutrient, is toxic to animals and humans in high concentrations. The main pollutants are released by the process of smelting. Most copper ores are sulphur-based and smelting releases sulphur dioxide, an air pollutant known to have many harmful effects.
Sometimes, depending on the quality of the ore, the concentration of sulphur dioxide is so high that industries are forced to convert it into sulphuric acid, which itself is a water contaminant.
The other byproduct of smelting is slag, the waste matter separated from metals. This slag may leach heavy metals (arsenic, cadmium, lead, or mercury, depending on the ore’s composition) into groundwater reservoirs. Water with high heavy metal content is very toxic to humans.

Sulphur dioxide is a toxic gas with a pungent, irritating smell. It contributes to acid rain.
It is released naturally by volcanic activity. It is abundantly available in the atmosphere of Venus.
Sulphur dioxide is primarily produced for sulfuric acid manufacture.
Inhaling sulphur dioxide is associated with increased respiratory symptoms and premature death.
It also weakens the functioning of certain nerves.
It is also produced by
- burning coal in thermal power plants and diesel fuels.
- some industrial processes, such as the production of paper and smelting of metals.
- reactions involving Hydrogen Sulphide (H2S) and oxygen.
- The roasting of sulphide ores such as pyrite, sphalerite, and cinnabar (mercury sulphide).

Statement 1 can be eliminated using the “extreme wording” rule — the term “lethal quantities” is a strong, absolute claim and is unlikely in such contexts. UPSC generally avoids such exaggerations unless clearly established. In contrast, Statements 2 and 3 use moderate terms like “can” and “may”, which are more realistic in environmental science questions, making them more reliable.