Some<unk>  chemicals are valued for various uses, the most common of which is in household cleaning agents. For example, most drain cleaners contain either acids or alkalis due to their capabilities of dissolving greases, proteins or mineral deposits such as limescale inside water pipes. In chemical uses, high chemical reactivity is often desirable, as the rates of chemical reactions depend on the activity (effective concentration) of the reactive species. For instance, catalytic sulfuric acid is used in the alkylation process in an oil refinery: the activity of carbocations, the reactive intermediate, is higher with stronger acidity, and thus the reaction proceeds faster. Once used,<unk> s are most often recycled or neutralized. However, there have been environmental problems with untreated<unk>  effluents or accidental discharges.
Corrosive substance
Inhalant
Organochlorine compound
Allergen
Cold medicine
Organobromine compound
Persistent organic pollutant
Toxicant