By Dr Sk Faizan Ali Benzene - PowerPoint Presentation

Slide1

ByDr Sk Faizan Ali

Benzene

AROMATIC HYDROCARBONS--------BenzeneSynonymsBenzol, Benzole, Benzolene, Coal naphtha, Phenyl hydride, Annulene, Carbon oil, Cyclohexatriene, Mineral naphtha,Motor benzol, Phene, Pyrobenzol, Pyrobenzole.Physical AppearanceColourless, volatile, inflammable liquid, with a strong, pleasant odour.Sources■ Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural constituent of crude oil.■ Benzene can be recovered from coal tar and produced from the hydrodemethylation

of toluene under catalytic or thermal conditions.

■ A chief source of benzene is catalytic reformat, wherein the naphthenes and paraffins contained in naphtha are converted to aromatic hydrocarbons. Solvent extraction is then used to recover the benzene.■ Most of the benzene produced is generally derived from the petrochemical and petroleum-refining industries.■ Cigarette smoke also is said to contain benzene.Uses■ Benzene is extensively used in industry for the manufacture of drugs, chemicals, insecticides, glues, varnishes, paints, polishes, explosives, batteries, shoes, and rubber tyres.■ It is also used in printing, photography, and dry cleaning.■ It is a popular solvent in laboratories.■ Petrol often has significant concentrations of benzene.

Clinical Features1. Acute Exposure:a. Benzene can be absorbed through all routes.b. Most individuals can begin to smell benzene in air at 1.5 to 4.7 parts per million (ppm) and detect the odour of benzene in water at 2 ppm.c. Brief exposure (5 to 10 minutes) to very high benzene air concentrations (10,000 to 20,000 ppm) can result in death.d. On inhalation ,principal manifestations include vertigo, tinnitus, vomiting, dyspnoea, convulsions, coma, and death. Cardiac arrhythmias are possible.e. On ingestion, burning pain in the mouth and pharynx, epigastric pain, vomiting, vertigo, tachycardia, hypotension, dyspnoea, convulsions and

coma.f. Aspiration produces similar manifestations as in the case of aliphatic hydrocarbons.g. Locally (on skin), benzene has a strong irritating effect, producing erythema, burning and, in more severe cases, oedema and blistering.2. Chronic Exposure:a. Benzene -human carcinogen,These include aplastic anaemia, acute myeloblastic leukaemia, haemolytic

anaemia

, and

pancytopenia

. Benzene exposure is associated with translocations between chromosomes 8 and 21, and

hyperploidy

. These

aberrations may be involved in benzene-induced

leukaemia

.

b. Headache, dizziness, irritability, nervousness, fatigue, anorexia and epistaxis may also occur with chronic benzene poisoning.c. Paroxysmal nocturnal haemoglobinuria (PNH) is often associated with aplastic anaemia and rarely with acute leukaemia.d. Insulin-dependant diabetes mellitus e. An epidemiological study of pregnant women in a large petrochemical industry showed a positive

correlation between

reduced birth weight and exposure to

benzene and

work stress.

DiagnosisBenzene is metabolised extensively in the liver and excreted in the urine, with 51 to 87% excreted as phenol,6% as catechol, and 2% as hydroquinone. Monitoring benzene in expired air and urine phenol levels may be useful for observing workers exposed to benzene.2. Analysis of urinary t, t-muconic acid appears to be a better indicator than phenol for assessment of exposure to low levels

of benzene

.

3. Gas chromatography head-space analysis is the

preferred method

for determining benzene in blood or urine.

The lower

limit of detection is 0.64

nmol

/L for benzene in

blood and

0.51

nmol

/L in urine.

4. Obtain baseline CBC.

5. Monitor ECG for cardiac arrhythmias.

Treatment – Acute exposure is treated on the same lines as in the case ofaliphatic hydrocarbons.1. Ipecac-induced emesis is not recommended because of the potential for CNS depression and seizures.2. Consider pre-hospital administration of activated charcoal as an aqueous slurry in patients with a potentially toxic ingestion who are awake and able to protect their airway.3. Consider gastric lavage with a large-bore orogastric tube after a potentially life-threatening ingestion if it can be performed soon after ingestion (generally within 60 minutes).

4. Remove contaminated clothing and wash exposed area extremely thoroughly with soap and water.5. Administer 100% humidified supplemental oxygen, perform endotracheal intubation and provide assisted ventilation as required. Administer inhaled beta adrenergic agonists if bronchospasm develops. Exposed skin and eyes should be flushed with copious amounts of water.6. Treat convulsions in the usual manner.