Xylene is an aromatic
hydrocarbon widely used in industry and medical technology as a solvent. It is a
colorless, sweet-smelling liquid or gas occurring naturally in petroleum, coal
and wood tar, and is so named because it is found in crude wood spirit . It has
a chemical formula of C6 H4 (CH 3)2 and is referred to as “dimethyl benzene”
because it consists of a six-carbon ring to which two methyl groups are bound.
It exists in three isomeric forms: ortho-, meta- and para-xylene.
Xylene is used as a solvent in the printing, rubber, paint and leather
industries. It is found in small amounts in airplane fuel, gasoline and
cigarette smoke. In dentistry, xylene is used in histological laboratories for
tissue processing, staining and cover slipping and also in endodontic
retreatment as a guttapercha solvent. Its high solvency factor allows maximum
displacement of alcohol and renders the tissue transparent, enhancing paraffin
infiltration. In staining procedures, its excellent dewaxing and clearing
capabilities contribute to brilliantly stained slides.
Exposure to xylene can occur via inhalation, ingestion, eye or skin contact. It
is primarily metabolized in the liver by oxidation of a methyl group and
conjugation with glycine to yield methyl hippuric acid, which is excreted in the
urine. Smaller amounts are eliminated unchanged in the exhaled air. There is a
low potential for accumulation. Xylene causes health effects from both acute
(<14 days) and also chronic (>365 days) exposure. The type and severity of
health effects depends on several factors, including the amount of chemical you
are exposed to and the length of time you are exposed for. Individuals also
react differently to different levels of exposure
The main effect of inhaling xylene vapor is depression of the central nervous
system, with symptoms such as headache, dizziness, nausea and vomiting. The
effects listed below can begin to occur with exposure to air levels of about 100
ppm. They are reversible and become more noticeable and serious as the length of
time of exposure increase
Irritation of the nose and throat can occur at approximately 200 ppm after 3–5
min. Accidental splash in the eye may damage the surface of the eye, which will
heal within a few days
Exposure to xylene at levels of 200 ppm or greater can irritate the lungs,
causing chest pain and shortness of breath. Extreme overexposure (e.g., in a
confined space) can result in pulmonary edema, a potentially life-threatening
condition in which the lungs fill with fluid. However, there is no evidence that
repeated, low-level exposure has any long-term effects on the lung
At very high levels of exposure, xylene can injure the liver and kidneys, but
this is extremely unlikely to happen without noticeable effects on the nervous
system. Generally, such damage is reversible. Low-level occupational exposure
does not affect the liver and the kidneys.
Preventive measure
Substitution
Local exhaust ventilation
Proper protective equipment
Substitution means finding a substance that can perform the same function and
which may lessen the hazard. Care should be taken not to introduce any new
hazards when selecting a substitute for a hazardous material. After the
hazardous effects of xylene became indisputable in the 1970s, many potential
substitutes became available, some with as many if not more hazards. In general,
these substitutes fall into four classes and are marketed under various
tradenames. The chemical components are one of the following:
Limonene reagents
Aliphatic hydrocarbon mixtures
Aromatic hydrocarbon mixtures
Mineral oil mixtures
Conclusion
Efforts to reduce the health hazards in the histology laboratories should be
made to create a safer working atmosphere by making the histopathology
technicians more familiar with the health hazards of xylene, safety measures and
emergency procedures. The hazards of xylene are well documented, but the
substitutes are not so thoroughly evaluated. Most of the less-expensive
alternatives to xylene do not have the same miscibility with alcohol, wax and
resinous mountants, and nearly all are sold under trade names without any
obvious disclosure of the chemicals of which they are composed. The assumption
that they are safe just because the manufacturer says so is ill advised. It may
not be comforting to get exposed on a daily basis to large volumes of a product
of unknown chemical composition and largely untested health effects. Usage of
proper personal protective equipment and a decent fume hood prevents the
hazardous effects of xylene. In view of the established adverse effects of
xylene, the Indian Association of Occupational Hygiene should make a law to
safeguard the histopathology technicians against occupational hazards.