Benzidine, (4,4′-diaminobiphenyl), is the solid organic compound with the formula (C6H4NH2)2. [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”] It is a manufactured chemical that does not occur naturally. Benzidine is a crystalline (sandy or sugar-like) solid that may be greyish-yellow, white, or reddish-grey. It will evaporate slowly from water and soil. Its flammability, smell, and taste have not been described. In the environment, benzidine is found in either its “free” state (as an organic base), or as a salt (for example, benzidine dihydrochloride or benzidine sulphate). In air, benzidine is found attached to suspended particles or as a vapour.  Benzidine has been linked to bladder and pancreatic cancer. Since August 2010 benzidine dyes are included in the EPA’s List of Chemicals of Concern.
In the past, industry used large amounts of benzidine to produce dyes for cloth, paper, and leather. However, it has not been made for sale in the United States since the mid-1970s. Major U.S. dye companies no longer make benzidine-based dyes. Benzidine is no longer used in medical laboratories or in the rubber and plastics industries. However, small amounts of benzidine may still be manufactured or imported for scientific research in laboratories or for other specialised uses. Some benzidine-based dyes (or products dyed with them) may also still be brought into the United States.
In the Environment 
In the past, benzidine entered the environment largely when it was being made or used to produce dyes. Industry released it to waterways in the form of liquids and sludges, and transported benzidine-containing solids to storage or waste sites. Benzidine was sometimes accidentally spilled, and it was released to the air as dust or fumes. For the most part, companies no longer make or use benzidine, and the government strictly regulates these activities. Today, most benzidine still entering the environment probably comes from waste sites where it had been disposed. Some may also come from the chemical or biological breakdown of benzidine-based dyes or from other dyes where it may exist as an impurity. Only very small amounts of free benzidine will dissolve in water at moderate environmental temperatures. When released into waterways, it will sink and become part of the bottom sludge. Benzidine salts can dissolve more easily in water than free benzidine. Only a very small portion of dissolved benzidine will pass into the air. Benzidine exists in the air as very small particles or as a vapor, which may be brought back to the earth’s surface by rain or gravity. In soil, most benzidine is likely to be strongly attached to soil particles, so it does not easily pass into underground water. Benzidine can slowly be destroyed by certain other chemicals, light, and some microorganisms (for example, bacteria). Certain fish, snails, algae, and other forms of water life may take up and store very small amounts of benzidine, but accumulation in the food chain is unlikely.
Sources & Routes of Exposure
Sources of Exposure 
The general population is not likely to be exposed to benzidine through contaminated air, water, soil, or food. Benzidine is a manufactured chemical that does not occur naturally in the environment. Currently, the United States industry makes and uses very little (if any) benzidine, and no releases to air, water, or soil are reported on the Toxic Release Inventory (TRI). Only rarely has benzidine been detected in areas other than waste sites, and it has not been found in food. Some dyes used to colour foods or drinks may contain impurities that can be broken down to benzidine once inside the body. If you live near a hazardous waste site, you could be exposed to benzidine by drinking contaminated water or by breathing or swallowing contaminated dust and soil. Benzidine can also enter the body by passing through the skin. Some quantities of dyes made from benzidine may still be brought into the United States. These may contain small amounts of benzidine as a contaminant, or chemicals that may be broken down in the body to benzidine. If you use such dyes to dye paper, cloth, leather, or other materials, you may be exposed by breathing or swallowing dust, or through skin contact with dust. You may be exposed in a similar way if you work at or near hazardous waste sites.
Routes of Exposure 
Benzidine can enter your body if you breathe air that has small particles of benzidine or dust to which benzidine is attached. It can also enter your body if you drink water or eat food that has become contaminated with benzidine. If your skin comes in contact with benzidine, it could also enter your body. Generally, it will take only a few hours for most of the benzidine to get into your body through the lungs and intestines. It may take several days for most of the benzidine to pass through your skin. Breathing, eating, or drinking benzidine-based dyes may also expose you to benzidine. Your intestines contain bacteria that can break down these dyes into benzidine. Once in your body, only a small portion of benzidine will leave as waste in your urine and feces. Your body will change most of the benzidine into many different chemical forms (called metabolites), which dissolve readily in your bodily fluids and are easy for your body to remove. Some of these changed forms of benzidine appear to cause many of the chemical’s harmful effects. Studies show that after benzidine has entered your body, most of it (and its changed forms) will be removed within a week.
Health Effects 
No information is available on the acute effects of benzidine in humans via inhalation exposure. Benzidine is considered to be very acutely toxic to humans by ingestion. Symptoms of acute ingestion exposure include cyanosis, headache, mental confusion, nausea, and vertigo. Dermal exposure may cause skin rashes and irritation. Tests involving acute exposure of rats and mice have shown benzidine to have high toxicity from oral exposure.
Chronic Effects (Noncancer)
Chronic exposure to benzidine in humans may result in bladder injury. The Reference Dose (RfD) for benzidine is 0.003 milligram per kilogram body weight per day (mg/kg/d) based on brain cell vacuolisation in mice and liver cell alterations in female mice. The California Environmental Protection Agency (CalEPA) has established a chronic reference exposure level of 0.01 milligrams per cubic metre (mg/m3) for benzidine based on neurological, liver, and spleen effects in mice.
- Numerous epidemiologic studies have demonstrated occupational exposure to benzidine to result in an increased risk of bladder cancer.
- Animal studies have reported various tumour types at multiple sites from benzidine exposure via oral, inhalation, and injection exposure.
- EPA has classified benzidine as a Group A, human carcinogen.
First Aid Measures
- Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical attention.
- Skin Contact: In case of contact, immediately flush skin with plenty of water. Cover the irritated skin with an emollient. Remove contaminated clothing and shoes. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention.
- Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream. Seek medical attention.
- Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention.
- Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen tight clothing such as a collar, tie, belt or waistband.
Exposure Control/Personal Protection
- Use process enclosures, local exhaust ventilation, or other engineering controls to keep airborne levels below recommended exposure limits. If user operations generate dust, fume or mist, use ventilation to keep exposure to airborne contaminants below the exposure limit.
Personal Protective Equipment
The following personal protective equipment is recommended when handling benzidine:
- Splash goggles;
- lab coat;
- dust respirator (be sure to use an approved/certified respirator or equivalent); and
Personal Protection in Case of a Large Spill:
- Splash goggles;
- full suit;
- dust respirator;
- boots; and
- A self-contained breathing apparatus should be used to avoid inhalation of the product.
OSHA: The Occupational Safety & Health Administration has set the following Permissible Exposure Limit (PEL) for benzidine:
- General Industry: 29 CFR 1910.1010 requirements identical to 29 CFR 1910.1003 – 13 Carcinogens (4-Nitrobiphenyl, etc.) — Cancer-Suspect Agent
- Construction Industry: 29 CFR 1926.1110 requirements identical to 29 CFR 1910.1003 – 13 Carcinogens (4-Nitrobiphenyl, etc.) — Cancer-Suspect Agent
- Maritime: 29 CFR 1915.1010 requirements identical to 29 CFR 1910.1003 – 13 Carcinogens (4-Nitrobiphenyl, etc.) — Cancer-Suspect Agent
ACGIH: The American Conference of Governmental Industrial Hygienists has set the following threshold Limit Value (TLV) for benzidine: Exposure by all routes should be carefully controlled to levels as low as possible; Skin; Appendix A1 – Confirmed Human Carcinogen
NIOSH: The National Institute for Occupational Safety and Health has set the following Recommended Exposure Limit (REL): Appendix A – NIOSH Potential Occupational Carcinogens; Appendix C – Supplementary Exposure Limits