Hydrocarbons toxicity
Hydrocarbons are organic compounds that contain hydrogen and carbon.
They may be divided into aliphatic (straight chain); or aromatic (benzene
ring) compounds; and halogenated (aliphatic and aromatic) hydrocarbons.
Examples of hydrocarbons
1- Aliphatic
Gases: methane, propane, butane.
Liquid: hexane, octane.
Waxes: paraffins.
2- Aromatics
Benzene, toluene,xylene, styrene, vinyl chloride.
3- Halogenated hydrocarbons
Aliphatic: chloroform, carbon tetrachloride.
Aromatic:
lindane.
dichloro-diphenyl-trichloethane
(DDT),
chlordane,
4- Petroleum distillates: petroleum ether (benzene), gasoline,
nephtha, kerosene, fuel oil, paraffin.
5- Distillate of pine wood: turpentine.
6- Distillate of coal tar: benzene, toluene, xylene.
Characteristics of hydrocarbons
Each hydrocarbon has unique characteristics including molecular weight,
volatility, surface tension and viscosity.
Surface tension refers to cohesiveness of molecules on a liquid surface.
Volatility refers to the tendency of a liquid to change into gas or vapor.
Viscosity refers to the resistance of a substance to flow over a surface.
The most volatile hydrocarbons the low M.W. (C1-C5) gases and are
asphyxiants.
Aromatic hydrocarbons such as benzene, toluene and xylene are also
volatile and well absorbed from GIT, they can produce systemic toxicity
if absorbed. Some petroleum distillates are highly volatile but generally
poor absorbed after ingestion. Inhalation of their fumes may cause CNS
depression.
Mechanism of toxicity
The two most common routes of exposure to hydrocarbons inhalation and
ingestion, ingestion is the more common one. Hydrocarbons ingestion
produces toxic effects in the pulmonary, CNS, gastrointestinal, hepatic,
and cardiovascular systems; pulmonary system is the most seriously
damaged due to aspiration pneumonitis.
Halogenated hydrocarbons particularly those containing fluorine sensitize
the heart to catecholamines and induce arrhythmias in susceptible
individuals.
Petroleum distillate and turpentine
Petroleum distillate ingestion involves a relatively small number of
poisoning and not all of them are of aspiration risk. High viscous
substances e.g. paints, glues, asphalt, rubber, cement etc. have little
significant hazard of aspiration. Obstruction occurs greatly after ingestion
of highly viscous product. Compounds with low viscosity and high
volatility such as gasoline, kerosin have greater risk of aspiration.
Pathogenesis
1- Gastrointestinal tract: produce GI irritation and burning, often
resulting in emesis and risk of aspiration.
2- CNS: CNS depression after hydrocarbons ingestion is due to a
direct effect on the CNS or occurs secondary to hypoxic cerebral
damage resulting from chemical-induced pneumonitis.hughly
volatile hydrocarbons as gasoline, benzene, toluene, turpentine and
xylene are associated with greater risk of CNS toxicity because of
their high lipid solubility. However large amount need to be
swallowed and absorbed to produce significant CNS effects, they
have a disagreeable taste and large volume and rarely ingested.
3- Respiratory system: pulmonary toxicity is primarily related to the
aspiration of hydrocarbons during or after ingestion and vomiting.
The risk of aspiration and lung damage is directly proportional to
volatility and indirectly related to surface tension and viscosity.
Hydrocarbons that most likely to be aspirated are highly volatile
and have low surface tension and viscosity, these properties permit
the hydrocarbons to move up the wall of the esophagus and enter
the trachea.
Characteristics of poisoning
1- Petroleum distillate and turpentine:
Acute (inhalation, ingestion)
GIT: nausea, vomiting, burning sensation, odor on breath.
Respiratory: cough, shortness of breath, dyspnea, pulmonary
edema and aspiration pneumonitis.
CNS: Dizziness, depressed reflex, unconsciousness and
convulsions.
Chronic inhalation
Dizziness, anemia, weakness, weight loss and parasthesia.
2- Aromatic hydrocarbons