Chapter 24

• The term solvent refers to a class of liquid organic chemicals of variable lipophilicity and volatility, small molecular size, and lack of charge.
• Absorption of inhaled volatile organic compounds occurs in the alveoli, with almost instantaneous equilibration with blood in the pulmonary capillaries.
• Solvents are readily absorbed from the gastrointestinal tract and across the skin.
• Most solvents produce some degree of CNS depression.

The term solvent refers to a class of liquid organic chemicals of variable lipophilicity and volatility, small molecular size, and lack of charge. Solvents undergo ready absorption across the lung, skin, and gastrointestinal (GI) tract. In general, the lipophilicity of solvents increases with increasing molecular weight, while volatility decreases. Solvents are frequently used to dissolve, dilute, or disperse materials that are insoluble in water. Most solvents are refined from petroleum. Many, such as naphthas and gasoline, are complex mixtures consisting of hundreds of compounds.

Solvents are classified largely according to molecular structure or functional group. Classes of solvents include aliphatic hydrocarbons, many of which are chlorinated (i.e., halocarbons), aromatic hydrocarbons, alcohols, ethers, esters/acetates, amides/amines, aldehydes, ketones, and complex mixtures that defy classification. The main determinants of a solvent's inherent toxicity are: (1) its number of carbon atoms; (2) whether it is saturated or has double or triple bonds between adjacent carbon atoms; (3) its configuration (i.e., straight chain, branched chain, or cyclic); and (4) the presence of functional groups. Subtle differences in chemical structure can translate into dramatic differences in solvent toxicity.

Nearly everyone is exposed to solvents during normal daily activities. Environmental exposures to solvents in air and groundwater use multiple exposure pathways (Figure 24–1). Though not reflected in Figure 24–1, household use of solvent-contaminated water may result in solvent intake from inhalation, and dermal and oral absorption. In many cases, environmental risk assessment requires that risks be determined for physiologically diverse individuals who are exposed to several solvents by multiple exposure pathways.

###### Figure 24–1

Solvent exposure pathways and media. (From EPA: Risk Assessment Guidance for Superfund. Human Health Evaluation Manual Part A, Interim Final. Washington, DC: Office of Emergency and Remedial Response, 1989.)

The Occupational Safety and Health Administration (OSHA) has established legally enforceable Permissible Exposure Limits (PELs) for over 100 solvents. The majority of existing PELs were adopted from the list of Threshold Limit Values (TLVs) published by the American Conference of Governmental Industrial Hygienists (ACGIH). Whereas the ACGIH's TLVs for an 8-h work day, 40-h work week are designed to be protective for a working lifetime, its Short-term Exposure Limits (STELs) and ceiling values are designed to protect against the acute effects of high-level, short-term solvent exposures. If warranted, the ACGIH will assign a skin notation to a solvent, indicating that significant dermal exposure is possible.

Most solvent exposures involve a mixture of chemicals, ...

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