Fact Sheet

Fact Sheet: Benzidine-Based Chemical Substances

Benzidine and its related chemical substances are used to manufacture dyes. Benzidine-based dyes are used in the production of textiles, paints, printing inks, paper, and pharmaceuticals. They are also used as reagents and biological stains in laboratories, and have more recent uses in laser, liquid crystal displays, ink-jet printers, and electro-optical devices.

Benzidine and dyes that can be metabolized to benzidine, which is classified as a known human carcinogen. EPA

Exposure to benzidine-based dyes are of concern to consumers, workers and children because benzidine dyes can be converted in the body into a chemical that is known to cause cancer. 

Benzidine is rapidly absorbed through the skin in solid and vapor form. It is also quickly absorbed through the lungs on inhalation and from the gastrointestinal tract on consuming contaminated water and food. Generally, it will take only few hours for most of the benzidine to get into the body through the lungs and intestine. Breathing, eating, or drinking benzidine-based dyes may also expose a person to benzidine because the intestinal bacteria can break down these dyes into benzidine. It is a lipophilic substance, hence easily stored in fat tissues, and it firmly binds to cell receptors. Benzidine is metabolized to aromatic amine by intestinal microflora or liver azo-reductase. The liver is the chief organ of metabolism where benzidine is converted to more reactive, toxic, and mutagenic (carcinogenic) N-hydroxyarylamides and N-hydroxylamine is considered to be a proximate carcinogen. NHydroxylamides are converted to the ultimate carcinogens through conjugation with sulfuric, acetic, or glucuronic acids. NAcetoxyarylamines are also produced as metabolites and are highly reactive mutagens and carcinogens. Glutathione transferase plays an important role in the elimination of reactive metabolites of benzidine. Sulfonation, carboxylation, deamination, or substitution of an ethyl alcohol or an acetyl group for the hydrogen in the amino groups leads to a decrease in mutagenicity of benzidine metabolites as well as to easy elimination, primarily through urine and feces.