Hydrocarbons

Overview

Hydrocarbons are a diverse group of organic compounds that contain hydrogen and carbon ( Table 147.1 ). Most hydrocarbons (such as gasoline) are byproducts of crude oil and are therefore called petroleum distillates. Essential oils such as turpentine or wormwood are derived from plants. Hydrocarbons are used as solvents and diluents in many products, including household cosmetics and chemicals, pesticides and fuels. The two main categories of hydrocarbons are aliphatic (straight chain structures, such as propane) and aromatic (cyclic structures, such as toluene). Hydrocarbons can also have multiple nonorganic side chains. For example, halogenated hydrocarbons will have at least one bromide, chloride, fluoride, or iodide moiety (e.g., carbon tetrachloride). Finally, hydrocarbons are used as a solvent base for many toxic chemicals, such as insecticides, carburetor cleaner (methanol), and heavy metals, which in turn can cause separate distinct syndromes of poisoning. Although there is a wide variety of toxic hydrocarbons, the majority of human exposures are confined to petroleum distillates.

Human exposure, both intentional and unintentional, to hydrocarbons is a common problem. In 2018, U.S. poison centers reported over 28,500 exposures to hydrocarbons accounting for over 1% of all calls with 121 major outcomes and 20 deaths. Over the prior decade, there were approximately 4000 pediatric exposures to hydrocarbons per year, and almost 10% were hospitalized. It is estimated that nearly 10% of the United States population aged 12 years and older have used an inhalant for its psychoactive properties. Toxic exposure to hydrocarbons is dermal, inhalational, or via ingestion (with potential for aspiration). Inhalational exposures are typically due to either intentional abuse of volatile hydrocarbons (huffing, sniffing, dusting or bagging) or household and workplace exposures. Ingestions are mostly accidental pediatric exposures, which can lead to aspiration pneumonitis. Dermal exposures are from household or workplace use of hydrocarbon-based agents and are rarely intentional.

Pathophysiology

Hydrocarbons are local gastrointestinal irritants, but acute toxicity usually manifests through effects on three main target organs: lungs, heart, and central nervous system (CNS). Most ingestions of hydrocarbons do not lead to serious systemic toxicity but localized gastrointestinal symptoms such as abdominal pain, vomiting, and diarrhea may occur. Exceptions include halogenated or aromatic hydrocarbons, and hydrocarbons containing metals or pesticides, which are capable of causing significant CNS, hepatic, or renal toxicity. Despite the fact that there are thousands of different types of hydrocarbons, their potential for acute toxicity depends on a few physical properties:

• Viscosity is the capacity to resist flow or change. Low-viscosity hydrocarbons, such as gasoline, lamp oil, and furniture polish, spread rapidly into the airway, with high risk of aspiration toxicity. Lubricants and mineral oil, conversely, have high viscosity and low aspiration potential.

• Volatility is a measure of a liquid’s ability to evaporate to a gas or vapor. Hydrocarbons with high volatility can displace alveolar oxygen and cause hypoxia. Butane and propane are examples of hydrocarbons with high volatility.

• Surface tension is the capacity for a liquid to adhere to a surface. Low surface tension, like low viscosity, enables a substance (e.g., turpentine) to disperse easily and may lead to pulmonary toxicity.

• Chemical side chains or substitutions often increase potential toxicity. These include metals (e.g., lead), halogens (e.g., the chloride ions in carbon tetrachloride), and those found on aromatic structures (e.g., the CH ₃ groups in toluene and xylene). Halogenated hydrocarbons may cause cardiotoxicity.

• Lipophilicity enhances blood brain barrier penetration resulting in CNS effects.