Aniline

Aniline was first isolated from coal tar in 1826 and became one of the most important industrial chemicals of the 19th century as a dye precursor — aniline dyes launched the synthetic textile dye industry [1]. Today the majority of aniline production goes to methylene diphenyl diisocyanate (MDI) for polyurethane production, with smaller amounts used in rubber additives, agricultural chemicals, and pharmaceuticals. About 7 billion pounds are produced annually globally [2]. Production facilities are concentrated in the Gulf Coast region. Aniline contamination of soil and groundwater occurs near manufacturing facilities and from historical waste disposal. Aniline can also be formed from environmental reduction of nitrobenzene in anaerobic conditions [3].

Occupational inhalation and skin absorption in aniline manufacturing, rubber processing, and dye manufacturing are the primary routes [1]. Aniline is readily absorbed through both inhalation and skin contact — a spill on skin can cause significant systemic toxicity. Community air near production facilities and nitrobenzene reduction in contaminated groundwater are environmental sources [2]. Consumer exposure from products made with aniline-derived chemicals is generally very low once the final polymers or dyes are formed [3].

Aniline, like nitrobenzene, causes methemoglobinemia by oxidizing hemoglobin iron — producing cyanosis, weakness, and at high levels, cardiovascular collapse [1]. Bladder cancer is the primary long-term carcinogenic concern — aniline is metabolized to reactive ortho-aminophenols and hydroxylaminobenzene that accumulate in urine and react with bladder urothelium. The dye industry's bladder cancer epidemic of the early 20th century (sometimes called "aniline cancer") established aniline and related aromatic amines as bladder carcinogens [2]. IARC classifies aniline as Group 3 (inadequate evidence for classification), but given the strong mechanistic and structural analogy to known bladder carcinogens (benzidine, beta-naphthylamine) in the aromatic amine class, occupational exposure is treated with caution [3].

Workers in aniline production, MDI/polyurethane manufacturing, rubber processing, and dye manufacturing face occupational exposures [1]. People who had significant exposure to aromatic amines in dye manufacturing historically (especially those employed in the mid-20th century before modern controls) should be aware of elevated bladder cancer risk and discuss screening with their physician [2].

Workers in aniline environments: use enclosed systems and local exhaust ventilation; wear impermeable nitrile or neoprene gloves and chemical splash protection [1]. Regular urinalysis and urine cytology (checking for abnormal bladder cells) should be part of health monitoring for workers with significant aniline exposure history [2]. Community members near aniline production facilities should consult EPA's ECHO and Envirofacts databases for facility emission profiles [3].