Shadows Over Calixis
Slag fields are formerly vast agri fields that have fallen into disrepair for a multitude of reasons, least of which is the pollution made by industry seeping into the area and collecting in the fields, and rendering them useless.
over time the corrosive materials coalesce into large pools of slime, which corrode literally everything they touch , and further emits noxious vapors into the air.
Typically these fields are found in the under hives of large cities, where the atmosphere has completely changed into toxic chemicals, and permeated the lower levels of the hive.
Because of the toxic nature of these levels, especially around the slag fields because the permeable soil in the once agri fields soak up far more pollutants than the metal halls, only mutants with suitable mutations or those with respirators or re breathers can survive.