Aromatic Hydrocarbon Toxicity: Benzene and Toluene

Etiology

The effects of toluene and benzene toxicity is usually acquired through inhalation.

Inhalation occurs by three different methods[2]:

• Huffing: the individual soaks a rag with a chemical and then places it over the mouth and nose.
• Bagging: the individual puts the chemical in a bag and repeatedly inhales deeply from the bag.
• Sniffing: the chemical is directly inhaled via the nostrils. 

Epidemiology

Toluene is the most widely abused inhaled volatile drug. Abusers who seek its euphoric effect are typically teenagers and younger adults. According to the Toxic Exposure Surveillance System of the American Association of Poison Control Systems, 54% of the abusers of inhaled volatile substances were teenagers age 13 to 19 years old, and 15% were children aged 6 to 12 years old. In addition, there is a higher incidence of volatile substance abuse in states with larger rural populations and in lower socioeconomic groups.[3]

Pathophysiology

The toxic potential of hydrocarbons depends on the following:

• Physical Characteristics
  • Viscosity: thickness of a liquid. Fluids with low viscosity flow more easily.
  • Surface tension: the ability of liquid molecules to cohere to each other.
  • Volatility: the ability of a liquid or solid to vaporize.
• Chemical Characteristics
  • Aliphatic
  • Aromatic
  • Halogenated
• Presence of Toxic Additives
  • Pesticides
  • Heavy metals
• Routes of Exposure
  • Inhalation
  • Ingestion
  • Topical
• Concentration 
• Dose

Toluene and benzene are highly volatile aromatic hydrocarbons with a usual route of exposure in the form of inhalation. Inhalation of an aromatic hydrocarbon can result in systemic absorption and the potential for significant toxicity.[4]

Pulmonary Toxicity

All hydrocarbons, including toluene and benzene, can cause chemical pneumonitis by direct contact with the pulmonary parenchyma and destroying alveolar and capillary membranes. This results in vascular permeability and edema.

Cardiac Toxicity

All hydrocarbons can cause life-threatening dysrhythmias, such as ventricular tachycardia and ventricular fibrillation.

Central Nervous System Toxicity

Toluene causes euphoria followed by depression.

Renal and Metabolic Toxicities

Toluene specifically causes renal tubular acidosis. The typical metabolic profile is a normal anion gap hyperchloremic acidosis with hypokalemia and a urine pH of 5.5. Toluene’s metabolites, hippuric acid and benzoic acid, are possibly the cause for an elevated anion gap metabolic acidosis. In addition, toluene also causes hypokalemia leading to muscle weakness and if low enough, muscle paralysis. Rhabdomyolysis is a common complication.[5]

Hematological Toxicities

Exposure to benzene is associated with an increased incidence of hematologic disorders, such as aplastic anemia, acute myelogenous leukemia, and multiple myeloma.[6]

Toxicokinetics

Toluene

Toluene is inhaled via the lungs and distributed widely throughout the body, specifically adipose tissue, brain, liver, and kidneys. The liver converts toluene into organic acids. Toluene is metabolized by the cytochrome P-450 system. The end products include benzoic acid and hippuric acid. Hippuric acid is excreted by the kidney. Some toluene is excreted unchanged in expired air and urine.[7]

Benzene

Benzene is absorbed in the body through inhalation, skin exposure, and ingestion. It is rapidly metabolized in the liver, becomes water soluble, and is excreted by the kidneys within 48 hours. Benzene itself is non-toxic, but its metabolites form in the liver, specifically benzoquinone and malonaldehyde, have bone marrow toxicity.[8]

History and Physical

History

While taking the history, try to obtain the following information:

• To what drug or substance was the patient exposed?
• Was it intentional or accidental exposure?
• What was the route of exposure inhalation or ingestion?
• How long ago did exposure occur?
• How long was patient inhaling/ingesting the toxic substance?
• Did patient use or was exposed to any other toxic substance?

Physical Exam for Hydrocarbon Exposure[4]

After exposure to hydrocarbons, any of the following can be present: 

Pulmonary

• Tachypnea
• Grunting
• Wheezing
• Retractions

Cardiac

• Ventricular arrhythmias

Central nervous system

• Slurred speech
• Ataxia
• Lethargy
• Coma

Gastrointestinal

• Nausea
• Vomiting
• Abdominal pain 

Specific for toluene

• Headache
• Dizziness
• Confusion
• Muscle weakness and paralysis

Specific for benzene

• Lethargy
• Shortness of breath

Evaluation

There are no specific hydrocarbon tests in standard use when evaluating suspected hydrocarbon intoxication.[4]

When evaluating these patients, initial actions include:

• Cardiac monitor
• Pulse oximetry
• ECG

Laboratory tests include:

• Complete blood count
• Complete metabolic panel
• Arterial blood gas
• Creatine kinase

Radiographic tests include:

• Chest x-ray. However, Note that the initial radiograph in a symptomatic patient may be deceptively clear. Radiographic changes usually occur in 2 to 6 hours and are almost always present by 24 hours. The most common radiographic finding is bilateral infiltrates at the bases with multi-lobar involvement.

Treatment / Management

There is no specific antidote for toluene or benzene toxicity.[9][4][10](B2)

When treating these patients, the following actions should be taken:

• Contact poison control
• Secure airway
• Provide supplemental oxygen, if wheezing
• Administer B2-agonists, if wheezing
• Ventilatory support
• Treat hypotension with aggressive IV crystalloid fluid
• Treat hydrocarbon induced dysrhythmias with propranolol, esmolol, or lidocaine
• No benefit to gastric lavage or activated charcoal
• Correct electrolyte abnormalities
• Administer blood products as needed

Differential Diagnosis

• Acute Respiratory Distress Syndrome (ARDS)

• Alcohol Toxicity

• Aspiration

• Barbiturate Toxicity

• Benzodiazepine Toxicity

• Carbon monoxide poisoning

• Co-ingestions

• Inhalation injury

• Suicidality

• Toluene Toxicity

Surgical Oncology

• Acute respiratory distress syndrome (ARDS)

• Alcohol toxicity

• Aspiration

• Barbiturate toxicity

• Benzodiazepine toxicity

• Carbon monoxide poisoning

• Co-ingestions

• Inhalation injury

• Suicidality

• Toluene toxicity