Chapter 70 Petroleum Hydrocarbons
Petroleum is a highly complex mixture of hydrocarbons. “Petroleum poisoning” is actually the sum of the toxic effects and interactions of a mixture of disparate compounds. Although crude oil intoxication occurs in large animals and is a serious environmental problem, pets are most frequently exposed to more refined petroleum products. These include fuels such as propane, gasoline, kerosene, or diesel oil; solvents, such as paint thinner, engine degreaser, or laboratory chemicals; and lubricants, such as motor oil, waxes, or asphalt. Petroleum-based solvents are often used as “inert” carriers for a number of pesticides, paints, and medications. Petroleum-based chemicals are also the basic feedstock for products as diverse as plastics and pharmaceuticals. In other words, petroleum products represent a very diverse group of chemicals and are very widespread throughout the modern environment.
The precise composition of any specific petroleum product varies with its intended use and the characteristic process or processes used to produce it. For most of the simpler products like gasoline, the refining process consists largely of differential distillation and cracking. The product itself is defined in terms of boiling point rather than any specific composition. Thus, volatility provides one convenient index with which to broadly classify petroleum products. Some products, notably fuels with a high boiling point such as fuel oil, receive little further processing. Others, such as gasoline, are modified with a considerable number of additives, such as methanol or methyl tertbutyl ether, which possess significant toxic properties of their own. Finally, some products, such as the thermoplastics, are chemically modified to such an extent that their physical, chemical, and toxic properties are quite distinct from petroleum hydrocarbons as a whole. This last group is not included in this chapter. Conversely, some hydrocarbons of nonpetroleum origin, such as turpentine or linseed oil, are similar enough to be considered with petroleum-based solvents of similar molecular weight.
In people, the most frequent cause of petroleum poisoning involves substance abuse (e.g., using petroleum products to get “high”). Animals usually exhibit a little more common sense, but may still sample motor oil or gasoline out of curiosity if it is available. Inappropriate containers and failure to clean up spills are common sources of exposure to pets. Pets, especially cats, may ingest significant amounts of gasoline or other petroleum products via grooming and transdermally after topical exposure. Gasoline or kerosene are sometimes used in an attempt to remove sticky material, such as tar, from an animal’s coat. Many folk remedies contain inappropriate types and amounts of petroleum products. For example, a Doberman Pinscher came to a diagnostic laboratory after having been force-fed a mixture of gasoline and smokeless powder to make it more aggressive (the treatment was not successful).
The toxicity of a specific petroleum product theoretically varies with its composition. Given the huge number of distinct petroleum products in common use, it is impossible to track the toxicity of each individually. Fortunately, however, it is possible to make some broad generalizations about the toxicity of petroleum hydrocarbons on the basis of simple physical and chemical properties such as boiling point. Products with very high boiling points, such as asphalt, mineral oil, or waxes, are relatively nontoxic. In general the more volatile the compound, the more readily it is absorbed and thus the greater possibility for systemic toxicity. Very volatile compounds, such as benzene, also tend to be more readily aspirated and thus are more likely to cause chemical pneumonitis (Table 70-1).
|Acetone||Oral LD50: 5–10 mg/kg||CNS depression, narcosis, coma|
|Benzene||Oral LD50: 4 mL/kg||CNS depression, narcosis, bone marrow suppression|
|Carbon disulfide||Oral LD50: 5–10 mg/kg Inhalation LC50: 15 mg/L||Tremor, cyanosis, vascular collapse, coma|
|Cyclohexane||Oral LD50: >8 mL/kg||CNS depression, ataxia, narcosis, coma|
|Diesel fuel||Oral LD50: 9 mL/kg||Relatively nontoxic; diarrhea, GI upset|
|Gasoline||Oral LD50: 18 mL/kg||Moderate topical and GI irritant, aspiration pneumonia|
|Home heating oil||Oral LD50: 18 mL/kg||Relatively nontoxic; diarrhea, GI upset if dose is sufficient|
|Isopropanol||Oral LD50: 6–13 g/kg||CNS depression, ataxia, acidosis, coma|
|Jet fuel A||Oral LD50: >20 mL/kg||Relatively nontoxic; diarrhea, GI upset if dose is sufficient|
|Motor oil||Oral LD50: >22 mL/kg||Relatively nontoxic; diarrhea, GI upset if dose is sufficient|
|Toluene||Oral LD50: 6–8 mL/kg||CNS depression, ataxia, liver and kidney damage|
|Turpentine||Minimum lethal dose (children): 15 mL/kg||Strong irritant, readily absorbed through skin and by inhalation|
|Xylene||Oral LD50: 4 mL/kg||Strong topical irritant, CNS depression, tremors, coma|
The likelihood of pneumotoxicity is also determined by viscosity and surface tension. Lower viscosity enhances the penetration of the product into smaller and therefore more numerous airways. Low surface tension facilitates the spread of hydrocarbons over larger areas of pulmonary tissues. As little as 0.1 mL of a low-viscosity hydrocarbon-like mineral spirits, when aspirated directly into the trachea of dogs, may produce severe pneumonitis. In contrast, products with a high viscosity, such as motor oil, have a much more limited pneumotoxic potential (Box 70-1).
Box 70-1 Petroleum Products Listed in Order of Decreasing Viscosity
Hydrocarbon solvents, including petroleum distillates, turpentine, etc., are skin and eye irritants by virtue of their lipid solvent properties and are capable of producing erythema, dermatitis, and epithelial necrosis. Systemic toxicity should be considered following heavy dermal exposure, especially with strong solvents such as gasoline. This is especially important in small animals (e.g., pups or kittens), which have a relatively high body surface area to mass ratio. Again the relative toxicity of various products by this route of exposure seems to be inversely proportional to molecular weight and volatility. Toxicity is further enhanced by other factors such as long or matted hair that trap the hydrocarbon against the skin.