When It Comes To
Hydrocarbons, That's Where the US Government Draws the Line, No Matter How
Fatal They Might Be...
Hydrocarbons are a heterogenous group of organic substances that are primarily composed of carbon and hydrogen molecules. They are quite abundant in modern society; their use includes fuels, paints, paint and spot removers, dry cleaning solutions, lamp oil, lubricants, rubber cement, and solvents. In addition, many volatile substances that contain hydrocarbons
(eg, glue, propellants) are commonly abused for their euphoric effects.
Hydrocarbons can be classified as being aliphatic, in which the carbon moieties are arranged in a linear or branched chain, or aromatic, in which the carbon moieties are arranged in a ring. Halogenated hydrocarbons are a subgroup of aromatic hydrocarbons, in which one of the hydrogen molecules is substituted by a halogen group. The most important halogenated hydrocarbons include carbon tetrachloride, trichloroethylene,
tetrachloroethylene, trichloroethane, chloroform, and methylene chloride.
The hydrocarbons can be derived from either petroleum or wood. Petroleum distillates include kerosene, gasoline, and naphtha, while wood-derived hydrocarbons include turpentine and pine oil. The length of the chains as well as the degree of branching determine the phase of the hydrocarbon at room temperature; most are liquid, but some short-chain hydrocarbons
(eg, butane) are gas at room temperature, while other long-chain hydrocarbons
(eg, waxes) are solid at room temperature.
Toxicity from hydrocarbon ingestion can affect many different organs, but the lungs are the most commonly affected organ. The chemical properties of the individual hydrocarbon determine the specific toxicity, while the dose and route of ingestion affect which organs are exposed to the toxicity.
The recreational use of inhaling hydrocarbons and other volatile solvents for the purposes of creating a euphoric state is becoming increasingly common. There are several methods for this
misuse, including "sniffing" (directly inhaling vapors), "huffing" (placing a hydrocarbon-saturated
cloth over the mouth and nose and then inhaling), or "bagging" (inhaling
through an opening in a plastic bag filled with hydrocarbon vapors).
Pathophysiology
The toxicity of hydrocarbons is directly related to their physical properties, specifically the viscosity, volatility, surface tension, and chemical activity of the side chains. The viscosity is a measure of resistance to flow and is measured in Saybolt Seconds Universal
(SSU). Substances with a lower viscosity (SSU <60, eg, turpentine, gasoline, naphtha) are associated with a higher chance of aspiration. The surface tension is a cohesive force created by van der Waals forces between molecules and is a measure of a liquid's ability to "creep." Like the viscosity, the surface tension is also inversely related to aspiration risk; the lower the viscosity, the higher the risk of aspiration.
Volatility is the tendency for a liquid to change phases and become a gas. Hydrocarbons with a high volatility can vaporize and displace oxygen, which can lead to a transient state of hypoxia. Not surprisingly, the degree of volatility is directly related with the risk of aspiration. The amount of hydrocarbon ingested has not consistently been linked to the degree of aspiration, and hence pulmonary toxicity.
Toxicity from hydrocarbon exposure can be thought of as different syndromes, depending on which organ system is predominately involved. Organ systems that can be affected by hydrocarbons include the pulmonary,
neurologic, cardiac, gastrointestinal, hepatic, renal, dermatologic, and hematologic systems.
Pulmonary
Pulmonary complications, especially aspiration, are the most frequently reported adverse effect of hydrocarbon exposure. While the aliphatic hydrocarbons have little GI absorption, aspiration frequently occurs, either initially, or in a semidelayed fashion as the patient coughs or vomits, thereby resulting in pulmonary effects. Once aspirated, the hydrocarbons can create a severe
pneumonitis.
Hydrocarbon pneumonitis results from a direct toxic affect by the hydrocarbon on the lung parenchyma. The type II pneumocytes are most affected, and as such, surfactant production and function are altered. The end result of hydrocarbon aspiration is interstitial inflammation, intra-alveolar hemorrhage and edema, hyperemia, bronchial necrosis, and vascular necrosis.
Nervous system
CNS toxicity can result from several mechanisms, including direct injury to the brain, or indirectly as a result of severe hypoxia or simple asphyxiation.
Many of the hydrocarbons that affect the CNS directly are able to make their way across the blood-brain barrier because certain hydrocarbons are highly
lipophilic. In addition for individuals who are huffing or bagging, the act of rebreathing can result in
hypercarbia, which can contribute to decreased level of arousal.
Prolonged abuse of hydrocarbons can result in white matter degeneration (leukoencephalopathy). In addition, prolonged exposure to certain hydrocarbons
(eg, n-hexane or methyl-n-butyl ketone [MnBK]) can result in peripheral neuropathy.
Cardiovascular
Exposure to hydrocarbons can result in cardiotoxicity.
Most importantly, the myocardium becomes sensitized to the effects of
catecholamines, which can predispose the patient to tachydysrhythmias, which can result in syncope or sudden death.
Gastrointestinal
Many of the hydrocarbons create a burning sensation, as they are irritating to the GI mucosa. Vomiting has been reported in up to one third of all hydrocarbon exposures.
Hepatic
The chlorinated hydrocarbons, in particular carbon tetrachloride, are quite
hepatotoxic. Usually, the hepatotoxicity results after the hydrocarbon undergoes phase I metabolism, thereby inducing free radical formation. These free radicals subsequently bond with hepatic macromolecules and ultimately cause lipid
peroxidation. This metabolite creates a covalent bond with the hepatic macromolecules, thereby initiating lipid
peroxidation.
The common histopathologic pattern is centrilobular (zone III) necrosis.
Liver function test results can be abnormal within 24 hours after ingestion, and clinically apparent jaundice can occur within 48-96 hours.
Methylene chloride, a hydrocarbon commonly found in paint remover, is metabolized via the P450 mixed function oxidase system in the liver to carbon monoxide (CO). Unlike other cases of CO exposure, with methylene chloride, CO formation can continue for a prolonged period of time.
Renal
Chronic exposure to toluene, an aromatic hydrocarbon, can result in a distal renal tubular acidosis and present with an anion gap acidosis. A patient may have chronic exposure either via an occupational environment or by repeated recreational inhalation.
Hematologic
Prolonged exposure to certain aromatic hydrocarbons (especially benzene), can lead to an increased risk of aplastic anemia, multiple
myeloma, and acute myelogenous leukemia. In addition, hemolysis has been reported following the acute ingestion of various types of hydrocarbons.
Frequency
United States
In 2004, 54,766 cases of hydrocarbon poisoning were reported to US poison control centers. Of these, more than 27,000 were in patients aged 19 years or younger. Therefore, hydrocarbon ingestions account for just more than 2% of all calls to US Poison Control centers.
International
In developing nations, kerosene is implicated in approximately one third of pediatric poisonings.
Mortality/Morbidity
In 2004, 9 deaths due to hydrocarbons were reported to US poison control centers. This number is slightly decreased from recent years. In addition, however, several other deaths are classified as being due to "chemicals, cleaning substances, fumes/gases/vaporizers," and "pesticides." Thus, the true number is probably somewhere in the range of 15-20 deaths.
Age
Proportionately, more fatalities are associated with children younger than 5 years who often accidentally ingest hydrocarbons, and among adolescents, who are more likely to abuse volatile hydrocarbons.
Inhalant abuse is becoming increasingly common among adolescents. In one study, the lifetime prevalence for inhalant abuse for 8th graders was 17.1%.
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"Millions
of American could become addicted to gasoline overnight... from
adults to mere toddlers, there could be a thousand deaths in one weekend
from huffing gasoline, and many more could be hospitalized.... But no
matter what happens, you will never, ever see the day when gasoline
becomes a controlled substance. It's economically and politically
impossible."