108: Hydrocarbons

HISTORY AND EPIDEMIOLOGY

The modern world could not exist without hydrocarbons. Virtually everything we touch is either coated with or made up primarily of hydrocarbon products. Organic chemistry originated during the Industrial Revolution, evolving largely due to advances in coal tar technology. In the coking process, bituminous (soft) coal is heated to liberate coal gas. This gas contains volatile hydrocarbons that can be captured and separated into a variety of natural gases. The viscous residue left over from the coking process forms coal tar, which can, in turn, be distilled into kerosene and other hydrocarbon mixtures.

Over the years, petroleum has replaced coal tar as the principal source of commercial organic compounds. Crude oil processing involves heating to a set temperature within processors that separate (distill) hydrocarbon fractions by vapor (or boiling) point. Because of the relationship between boiling point and molecular weight, distillation roughly divides hydrocarbons into like sized molecules. The most volatile fractions come off early as gases, and these are used primarily as heating fuels. The least volatile fractions (larger than about 10 or 12 carbons) are used chiefly for lubricants or as paraffins, petroleum jelly, or asphalt. The remaining mid sized distillation fractions (5 to 10 carbons) are those most commonly used in combustion fuels and as solvents. Petroleum distillates are used as chemical feedstocks and as precursors or intermediates in feedstock production.

For decades in the United States, kerosene ingestion in children was a major public health concern.¹²¹ Only through public education, consumer product safety initiatives, and modernization of the use and distribution of cooking and heating fuels has this problem been largely eliminated. ­However, in the developing world, these same challenges have yet to be resolved, with large numbers of children ingesting kerosene from poorly labeled and poorly secured containers.^{1,18,19,46,63,93,109,125,137,159}

Recent public attention and debate surrounds the potential for hydrocarbon exposures following environmental spills. Even more controversial is the practice of “induced hydraulic fracturing” of rock or shale, commonly called “fracking.” Fracking is performed on up to 60% of oil and gas wells drilled today, to liberate pockets of trapped gas or oil from within the fractured rock.^103,165 The intent is to capture and collect trapped hydrocarbons, but some escape into nearby aquifers, thereby entering water supplies or otherwise contaminating human environments. Critics are concerned about the composition of the hydraulic fluids used, as these may be comprised mainly of methanol, ethylene glycol, benzene, or other hydrocarbons. Components of these fluids are found in area groundwater, with resultant risk of human exposure^62,175 and untoward health effects.⁹⁹

The true epidemiology of hydrocarbon exposure and illness is difficult to ascertain from available data sources. But three populations appear to be at particular risk for hydrocarbon related illness. These are ...