Formalin

A solution of formaldehyde in water, commercially available at 37–50% strength. Also known as formol. Used as a disinfectant, germicide and preservative for biological specimens; handling requires ventilation and protective equipment. Because of formaldehyde’s toxicity and carcinogenicity it has no permitted use in foods. In laboratories it fixes tissue specimens for histology, while in aquaculture it treats external parasites on fish — with strict withdrawal and environmental controls. Its pungent vapours irritate eyes and airways and it is a sensitiser, so occupational exposure limits apply; food-fraud use as a preservative is a criminal offence in most jurisdictions.