Organic solvents are a chemical class of compounds that are used routinely in commercial industries. They share a common structure (at least 1 carbon atom and 1 hydrogen atom), low molecular weight, lipophilicity, and volatility, and they exist in liquid form at room temperature. They may be grouped further into aliphatic-chain compounds, such as n -hexane, and as aromatic compounds with a 6-carbon ring, such as benzene or xylene. Aliphatics and aromatics may contain a substituted halogen element and may be referred to as halogenated hydrocarbons, such as perchloroethylene (PCE or PER), trichloroethylene (TCE), and carbon tetrachloride. Alcohols, ketones, glycols, esters, ethers, aldehydes, and pyridines are substitutions for a hydrogen group. Organic solvents are useful because they can dissolve oils, fats, resins, rubber, and plastics.
Organic solvents arose in the latter half of the 19th century from the coal-tar industry. Their application grew to be wide and diverse in both developed and developing countries. The introduction of chlorinated solvents in the 1920s led to reports of toxicity. Although solvents number in the thousands, only a few have been tested for neurotoxicity.
Workers in industries that use these agents may have occupational exposure, whereas other individuals may have environmental exposures if they live near industrial installations and/or have contact with contaminated water, soil, air, or food. Drinking water, shower water, ambient air, indoor air, and food, among other sources, are common routes of exposure to environmental toxins. Inhalation, ingestion, and dermal absorption are also important mechanisms of toxic exposure. [1, 2, 3] Exposures often involve mixtures of solvents. Some of these incidents may occur deliberately when an individual recreationally inhales paints, glues, and other products; these exposures are described in more detail in the Medscape Reference article Inhalants.
The Occupational Safety and Health Administration (OSHA) regulates worker exposure. The National Institute for Occupational Safety and Health (NIOSH) and the American Congress of Governmental Industrial Hygienists (ACGIH) also publish standards for use in occupational settings in the United States.
Short-term, high-level exposures such as those frequently reported in case reports can result in acute reversible and irreversible health effects that involve the CNS and PNS. In population studies, intermediate- and long-term, low-level exposures have led to reversible and nonreversible subclinical and clinical abnormalities in the CNS and PNS. In some cases, these exposures were estimated to be below acceptable levels, as designated in regulations for workers. Neurophysiologic, neuropsychological, and neuroimaging diagnostic tools have been used to evaluate individuals and groups exposed to organic solvents.
In 1987, NIOSH reported that 9.8 million workers were exposed to organic solvents in occupational settings. However, most occupational exposures involved solvent mixtures. Workers who use these agents include printers, paint manufacturers, painters, microelectronics workers, degreasers, dry cleaners, carpet layers, coating workers, gluers, dye workers, carpenters, anesthesia personnel, petrol filling workers, laboratory workers, inkers, and textile workers; others are those who work with polymers, pharmaceuticals, synthetic fabrics, agriculture products, refining, or in airplane refitting. Table 1 lists common sources of organic solvent exposures.
Table 1. Organic Solvents and Their Common Industrial Uses (Open Table in a new window)
|Acrylamide||Mining and tunneling, adhesives, waste treatment, ore processing|
|Benzene||Fuel, detergents, paint removers, manufacture of other solvents|
|Carbon disulfide||Viscose rayon, explosives, paints, preservatives, textiles, rubber cement, varnishes, electroplating|
|Ethylene oxide (ETO)||Instrument sterilization|
|N- hexane||Glues and vegetable extraction, components of naphtha, lacquers, metal cleaning compounds|
|Hydrogen sulfide||Sulfur chemical manufacturing, by-product of petroleum processing, decay of organic matter|
|Methyl mercaptan||Odorant in natural gas and fuels|
|Methyl-N- butyl ketone||Many industrial uses|
|Methylene chloride (dichloromethane)||Solvent, refrigerant, propellant|
|PCE||Dry cleaning, degreaser, textile industry|
|Styrene||Fiberglass component, ship building|
|Toluene||Paint, fuel oil, cleaning agents, lacquers, paints and paint thinners|
|1,1,1-Trichloroethane (methyl chloroform)||Degreaser and propellant|
|TCE||Cleaning agent, paint component, decaffeination, rubber solvents, varnish|
|Vinyl chloride||Intermediate for polyvinylchloride resins for plastics, floor coverings, upholstery, appliances, packaging|
|Xylene||Paint, lacquers, varnishes, inks, dyes, adhesives, cements, fixative for pathologic specimens|
Environmental exposures to organic solvents occur. Solvents are also present in home products. According to NIOSH, 49 million tons of organic solvents were produced in the United States in 1984. Contamination affecting community water supplies, food additives, or household chemicals is an important source of exposure. Well-water sampling, both in the United States and abroad, has revealed quantities of chlorinated hydrocarbons and other solvents. Health effects secondary to these exposures have been described.
Estimating rates of occupational exposure is difficult because of a variety of factors. Worker exposures vary even within the same job, exposures vary during a workday, many routes of absorption are possible, personal protective equipment (PPE) is used inconsistently, and solvents are commonly used in various mixtures. For environmental exposures, similar challenges exist. Industrial hygienists and risk-assessment scientists work to overcome these challenges.
Details of morbidity are available in the History section below.
Occupational exposures affect persons of working age. Environmental exposures affect persons of all ages.