Chapter 70 Petroleum Hydrocarbons
SOURCES
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.
TOXIC DOSE
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).
Table 70-1 Acute Toxicity of Some Commonly Encountered Hydrocarbons
| Compound | Dose | Clinical Signs |
|---|---|---|
| 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).
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.
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