What is Biphenyl?

Biphenyl (also known as diphenyl, phenylbenzene, 1,1'-biphenyl, or lemonene) is an organic compound that forms colourless crystals with a pleasant smell. It is an aromatic hydrocarbon with the molecular formula (C₆H₅)₂.

Biphenyl is known as a starting material for producing polychlorinated biphenyls (PCBs) and is also used as an intermediate in making various products such as

• Emulsifiers
• Optical brighteners
• Crop protection products
• Plastics

What are Biphenyl properties?

• Naturally found in coal tar, crude oil, and natural gas, and can be isolated by distillation
• Can be synthesised using a Grignard reagent (e.g., phenylmagnesium bromide + bromobenzene)
• Insoluble in water, but soluble in organic solvents
• Consists of two connected phenyl rings
• Lacks functional groups and is fairly non-reactive, but still undergoes benzene-like substitution reactions
• Thermally stable, but combustible at high temperatures:
  • Complete combustion: carbon dioxide and water
  • Incomplete combustion: carbon monoxide, smoke, soot, and low molecular weight hydrocarbons

In the Environment

• Poorly dissolves in water
• Mainly released into the air, where it either breaks down or settles onto land or water
• In water, it attaches to solids and is broken down by microorganisms
• In soil, it binds tightly and is unlikely to leach into groundwater
• Plants and animals may store small amounts

Sources and Routes of Exposure

How Exposure Occurs?

People can be exposed to biphenyl:

• In the workplace
• Through the environment (air, water, land, groundwater)
• By breathing contaminated air
• By eating or drinking contaminated food or water
• Through skin contact

Biphenyl does not stay in the body, as it is broken down and removed.

Sources of Biphenyl

Industry sources:

• Factories that produce, use, or handle biphenyl
• Used as a heat transfer agent, e.g. in electrical transformers

Diffuse sources and sub-threshold industrial sources

• Textile mills (used as a dye carrier, released in wastewater)
• Industrial processes
• Leaking heat exchangers
• Fumes from heat transfer use
• Volatilisation from soil and water

Natural sources:

• Found in trace amounts in crude oil

Consumer products:

• Used as a mould retardant in citrus fruit wrappers
• Found in plastics, optical brighteners, and hydraulic fluids
• Should not be intentionally present in consumer products
• May be found as a contaminant in food or dyed textiles

Health Effects

Acute Effects

In workers, short-term (acute) exposure to high levels of biphenyl has been associated with:

• Eye and skin irritation
• Toxic effects on the liver, kidneys, and both the central and peripheral nervous systems

Symptoms include:

• Headache
• Gastrointestinal pain
• Nausea
• Indigestion
• Numbness and aching in limbs
• General fatigue

Chronic Effects

In humans, long-term (chronic) exposure to biphenyl may cause:

Central nervous system symptoms, such as

• Fatigue
• Headache
• Tremor
• Insomnia
• Sensory impairment
• Mood changes
• These symptoms are rare

Reference Values:

• EPA has not established a Reference Concentration (RfC) for biphenyl
• Reference Dose (RfD): 0.05 mg/kg/day (based on kidney damage in rats)

Cancer Risk

• No human data is available on the carcinogenic effects of biphenyl
• EPA considers current animal studies on mice and rats to be inadequate
• One study in mice showed no increase in tumour incidence
• Another rat study found tumours in both treated and control groups, but they were not linked to biphenyl
• EPA classifies biphenyl as Group D: Not classifiable as to human carcinogenicity

Safety

First Aid Measures

Eye Contact:

• Remove contact lenses
• Rinse eyes with running water for at least 15 minutes, keeping eyelids open
• Get immediate medical attention

Skin Contact:

• Rinse skin with plenty of water for at least 15 minutes
• Remove contaminated clothing and shoes
• Apply an emollient to irritated skin
• Wash clothing and clean shoes before reuse
• Seek immediate medical attention

Serious Skin Contact:

• Wash with disinfectant soap
• Apply anti-bacterial cream
• Seek medical attention

Inhalation:

• Move to fresh air
• If not breathing, give artificial respiration
• If breathing is difficult, provide oxygen
• Get medical attention

Ingestion:

• Do not induce vomiting unless directed by medical personnel
• Never give anything by mouth to an unconscious person
• Loosen tight clothing (collar, tie, belt)
• Seek medical attention if symptoms appear

Exposure Control & Personal Protection

Engineering Controls

• Use process enclosures, local exhaust ventilation, or other controls to keep airborne biphenyl levels below exposure limits
• If work produces dust, fume, or mist, use ventilation to reduce exposure

Personal Protective Equipment (PPE)

When handling biphenyl:

• Splash goggles
• Lab coat
• Dust respirator (certified/approved)
• Gloves

In case of large spills:

• Splash goggles
• Full protective suit
• Dust respirator
• Boots
• Gloves
• Use a self-contained breathing apparatus (SCBA) to avoid inhaling the substance

Protective equipment may not be sufficient—consult a safety specialist before handling.

Exposure Limits

• TWA: 0.2 from ACGIH (TLV) [United States] [1995] 
• TWA: 1.3 from ACGIH (TLV) [United States] [1995]
• Worksafe Australia: Maximum 8-hour time weighted average (TWA) exposure: 0.2 ppm.