Handbook of Solvents - George Wypych - ChemTech - Ventech!

18.4 Solvent uses with exposure risks 1253
Most industrial countries have occupational exposure limits (OELs) for airborne concentrations
to prevent excessive exposures. The threshold limit values (TLVs) published by
the American Conference of Governmental Industrial Hygienists (ACGIH 15 ) are unofficial
but have had a great impact on OELs in the Western countries. These are updated annually
based on new epidemiological and toxicological data. Organic solvents are often used as
mixtures. Because the OELs for most solvents base on their neurotoxic properties, their effect
is considered to be additive and the combined exposure levels (or hygienic effects) are
calculated as the sum of the fraction of the OEL that each solvent represents. If the sum is
larger than one, a noncompliance situation exists. Compounds which may be dangerous by
uptake through the skin carry a skin notation. However, no quantitative dermal exposure
limits are available yet. Methanol, turpentine, glycol ethers, and many chlorinated and aromatic
hydrocarbons have the skin notation.
Exposures can also be assessed by analyzing biological specimens, such as blood or
urine. Metabolites of compounds are usually analyzed from urine samples. The amount of
biological exposure limits or indices (BEIs) is, however, much smaller than that for airborne
concentrations. However, biological monitoring may be useful although no BEI has been
established to ascertain effectiveness of personal protection or to follow exposure trend. Biological
monitoring reflects exposure via all routes. This is beneficial for individual exposure
assessment. Biological monitoring also reveals possible accumulation of a compound.
This is, however, of minor importance for most solvents because of their short half-lives.
The largest disadvantage of biological monitoring is that it does not provide any information
on the reasons of exposure. About twenty solvents have an ACGIH BEI (e.g., acetone,
carbon disulfide, 2-ethoxyethanol, n-hexane, methanol, methyl ethyl ketone,
perchloroethylene, styrene, toluene, trichloroethylene, and xylene). 15
Airborne concentrations of solvents are most commonly determined by taking samples
on adsorbents, such as activated carbon. Sampling can be done with a pump or passively
based on diffusion. In industrial working places where airborne concentrations of
solvents are on ppm-level, samples are generally extracted with a solvent (carbon disulfide
is the most common one). In offices and other nonindustrial environments where concentrations
are at ppb-level, samples are taken onto Tenax adsorption tubes which are desorbed
thermally. In both cases, gas chromatography is the most common analytical method. Because
the sampling time generally varies, it is important to calculate the time-weighted average
(TWA) concentration. TWA concentration is obtained by using the sampling times as
weights. Sampling and analysis has been reviewed e.g. by Soule. 16 Direct-reading instruments,
such as infrared or photoionic analyzers are good if only one solvent is present but
interferences may be a problem when solvent mixtures are analyzed.
Monitoring methods for dermal exposure have not been standardized as well as the
methods to assess inhalation exposure. Adsorptive pads of activated carbon cloth can be
used for monitoring of dermal exposure to organic solvents. Patches are attached on various
parts of the body under the clothing and the amounts analyzed are then multiplied with the
areas of each body region. 17 Exposure assessment is complicated by the contribution of solvent
vapor on the samples. Because the adsorptive surface of activated carbon is much
larger than that of the skin, pads will adsorb much more solvents than the skin. However,
only exposure to liquid phase is usually significant; therefore, the adsorbed vapor should be
subtracted from the total mass analyzed. 18 However, this makes the exposure assessment