From Unofficial Stationeers Wiki
Pollutant, also known as X, is produced when smelting certain metals. A concentration of 0.1Mol or greater will cause your suit to warn about pollutants/poison in the air, and it's not recommended to breath air containing Pollutant.
Pollutant has a specific heat of 24.8 Joule / mol, making it great for using as a Coolant.
You can collect Pollutant from the following sources:
|Copper Ore||1 mol|
|Gold Ore||2 mol|
|Iron Ore||2 mol|
|Lead Ore||2 mol|
|Nickel Ore||1 mol|
|Silicon Ore||1 mol|
|Silver Ore||1 mol|