n-hexane Toxicity

Excerpt

n-Hexane is a straight-chain hydrocarbon molecule commonly used as a solvent in various industrial applications. The paint and coating industries employ n-hexane in paint thinners and coatings for its ability to dissolve oils and resins. In the printing industry, the alkane is used in inks due to its quick-drying properties. The food processing industry relies on n-hexane for the extraction of vegetable oils from seeds and crops. In the shoemaking and textile industry, n-hexane is a component of glue and a solvent for cleaning and processing materials. This chemical's versatility makes it an essential component in many industrial applications.

Hydrocarbons like n-pentane and n-heptane are used for the same purposes as n-hexane. However, 6-carbon molecules like n-hexane are notorious for their significant neurologic toxicity. The general aspects, anatomical considerations, natural history, and patterns of spread associated with n-hexane toxicity are explained below.

General Information

n-Hexane exposure mainly occurs through inhalation, particularly in occupational settings like shoe factories where it is used as a solvent. Acute exposure to high concentrations can produce immediate symptoms, including lightheadedness, headache, and confusion, progressing to severe central nervous system (CNS) depression in extreme cases. Chronic exposure, however, poses a more insidious threat as the toxicity primarily stems from n-hexane's metabolites rather than the alkane itself. These metabolites, particularly 2,5-hexanedione, are implicated in the neurotoxic effects observed in workers.

Anatomy

The primary target of n-hexane toxicity is the peripheral nervous system. Once absorbed, n-hexane is metabolized in the liver to several other compounds, including 2-hexanol, 2,5-hexanediol, and, ultimately, 2,5-hexanedione. The aliphatic compound's neurotoxic effects are attributed to these metabolites, which interfere with normal nerve function. Histological examinations of affected individuals reveal n-hexane–induced axonal swelling, as well as accumulation of neurofilaments and nerve degeneration, particularly in the distal regions of the nerves.

Natural History

The progression of n-hexane–induced polyneuropathy has been well-documented over the past few decades. Initially found among shoe workers, the condition begins with nonspecific symptoms such as nausea, anorexia, and weight loss, followed by sensory disturbances like paresthesias in the lower extremities. Over time, the neuropathy progresses to flaccid paralysis and muscle atrophy, with significant impairment in motor and sensory conduction. Despite the cessation of exposure, recovery can be prolonged and is sometimes incomplete, with residual deficits persisting even after clinical recovery.