Xylene: The toxic solvent that caused poisoning in the last national exam 

Xylene is a clear, colorless sweet smelling liquid. It is widely used as a degreasing agent and as a thinner and solvent in paints, polish, inks, glues and adhesives; solvent in pesticide products and   medical technology.  

It is volatile, and readily produces toxic concentrations at room temperature. The vapor is heavier than air and may cause asphyxiation in enclosed, poorly ventilated, or low-lying areas. Making people of short stature and children more vulnerable to their toxic effects. Presumably, the toxic vapor accumulating at the ground level may have contributed to the dozens of reported cases of intoxication of students and invigilators in the last chemistry practical exam. 

Xylene’s odor generally provides adequate warning of hazardous concentrations. Xylene’s odor threshold is about 1 ppm, which is 100 times less than the accepted limit of exposure by regulatory authorities.  

It exists in three isomeric forms (ortho-, meta- and para-xylene) which are of relatively similar toxicity profile; laboratory grade xylene may contain other potentially harmful contaminants such as ethyl benzene, toluene, trimethyl benzene, phenol, thiophene, pyridine  and hydrogen sulfide 

Xylene reacts with strong oxidizers (eg bromine and bromates, potassium/sodium permanganate etc) and strong acids to cause explosive reactions. This likely to have been the reaction responsible for most of the explosions and severe burns reported in a number of candidates handling the product. 

As a result of their high volatility, people are mostly exposed to xylene by inhalation; they may also be exposed through the skin and by ingestion. However, ingestion and inhalation of xylene is associated with significant absorption, and systemic toxicity. Absorption through the skin is of least significance toxicologically (comprises 2% of the absorbed dose). 

Xylene is mostly 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; methyl  hippuric  acid has been used as an index of exposure for occupational monitoring (level of urinary methyl hippuric acid correlates to that of xylene exposure).  

Xylenes tend not to accumulate in the body, but they may be stored briefly in fat tissues due to their lipophilicity; elimination of xylene is hence slower in obese individuals. Most of the xylene that enters the body leaves within 18 hours after the end of the exposure. 

The primary effects of xylene exposure involve the nervous system by all routes of exposure; the respiratory tract by inhalation; but, at higher oral exposure levels, reversible hepatic and renal effects can occur. The severity of the effects depends on several factors, including the amount of exposure and the duration of exposure. 

At sufficiently high concentrations, inhalation of xylene produces irritant effects on the skin, eyes and mucous membranes.  

Skin exposure to liquid xylene produces skin irritation, erythema, and vasodilatation. Repeated contact, dissolves the skin’s natural protective oils to cause dermatitis, dryness, flaking and cracking of the  skin (damaged  skin  allow  greater  absorption of  chemicals). When splashed in the eyes, xylene may cause burning painful sensation, conjunctivitis, and corneal damage.  

Inhalation of xyline not only causes CNS effects but also induces toxic effects on the respiratory tract including Reactive Airway Dysfunction Syndrome (RADS), pulmonary haemorrhages and edema appearing 72 hrs after exposure. 

Regarding systemic effects, the most prominent and consistent in humans and animals is symptoms of CNS depression: headache, light-headedness, dizziness, confusion, nausea, loss of body balance, and blurred vision. More severe effects include tremors, rapid respiration, paralysis, loss of consciousness, coma, and death. Coma may persist long after exposure has ceased.   

Inhalation of massive doses of xylene can cause cardiac abnormalities, by potentiating the arrhythmogenic effects of adrenaline. Cardiac arrest has been reported in solvent abusers, often immediately after intense physical activity. 

If swallowed, xylene can irritate the stomach, causing nausea, vomiting, and diarrhea. 

During recovery, patients may continue to experience impaired gait, lightheadedness, dilated and poorly responsive pupils, and decreased or absent deep-tendon reflexes. Anxiety, fatigue, and insomnia may last several days. No long-term effects due to acute xylene exposure have been reported. 

Although the mechanism of toxicity is not well understood, CNS effects are attributed to the liposolubility of xylene in the neuronal membrane. It has been suggested that xylene disturbs the action of proteins essential to normal neuronal function either by disruption of the lipid environment in which the membrane proteins function or by direct interaction with the proteins in the membranes. 

Some authors have also suggested that certain metabolic intermediates such as methylbenzaldehyde may be responsible for the toxicity of xylene.  

First Aid Procedures  

In the event  of  an  emergency,  remove  the  victim  from  further exposure, send for medical assistance and initiate the following emergency procedures.   

Eye exposure:  If xylene or a solution containing xylene gets into the eyes, immediately  flush  the  eyes  with  large amounts  of  water  for  a  minimum  of  15  min,  lifting  the lower  and  upper  lids  occasionally.  Get medical attention as soon as possible. 

Skin exposure: The contaminated skin should be washed with  soap  and  water  for  at  least 15  min.  If irritation persists, get medical attention. 

Inhalation:  If xylene  vapors  are  inhaled,  move  the victim  at  once  to  fresh  air  and  get  medical  care  as  soon as  possible.  If the victim is not breathing, perform cardiopulmonary resuscitation; if breathing is difficult, give oxygen. Keep the victim warm and quiet until medical help arrives  

Ingestion:  If xylene or a solution containing xylene is ingested, give the victim several glasses  of  water  to drink. Get medical help immediately.  Keep the victim warm and quiet until medical help arrives. Do not induce vomiting if the person is unconscious as it is associated with the danger of pulmonary aspiration 

Management of acute exposure 

Persons whose clothing or skin is contaminated with liquid xylene can cause secondary contamination by direct contact or through off-gassing vapor; Remove all contaminated clothes and double bag them. 

Decontaminate the skin and eye exposure by thoroughly washing with tepid water or normal saline and mild soap. 

In case of oral exposure, emesis may be considered only when one there is no likelihood of aspiration of stomach contents i.e only done after protecting the airway. 

Use of activated charcoal in order to limit the absorption of the chemical in the intestines has been suggested by some authors. 

Haemodialysis and haemoperfusion in order to hasten the removal of xylene from the body may be considered in recalcitrant cases. 

Patients who have bronchospasm may be treated with aerosolized bronchodilators, preferably selective beta-2 agonists. However, the use of sympathomimetic agents such as epinephrine and isoprenaline could precipitate fatal arrhythmias, and should be avoided. 

Observe hospitalized patients for signs of acute tubular necrosis, encephalopathy, and arrhythmias. In addition, patients exposed by inhalation should be watched for signs of pulmonary edema, and those who have ingested xylene should be observed for signs of aspiration pneumonitis. 




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