PRINCIPLES OF TOXICOLOGY

372 PROPERTIES AND EFFECTS OF ORGANIC SOLVENTS
TABLE 16.3 Occupational Exposure Guideline Definitions
ACGIH: American Conference of Governmental Industrial Hygienists
TLV-TWA: threshold limit value—time-weighted average—time-weighted average concentration for a normal
8-h workday and a 40-h workweek, to which nearly all workers may be repeatedly exposed, day after
day, without adverse effects
STEL: short-term exposure limit—defined as 15 min TWA exposure that should not be exceeded during a
workday; concentration to which workers can be exposed continuously for a short period without suffering
irritation, chronic or irreversible tissue damage, or narcosis sufficient to increase likelihood of injury, impair
self-rescue or materially reduce work efficiency, provided the TLV-TWA is not exceeded
Categories for carcinogenic potential:
A1 Confirmed Human Carcinogen
A2 Suspected Human Carcinogen
A3 Animal Carcinogen
A4 Not Classifiable as a Human Carcinogen
A5 Not Suspected as a Human Carcinogen
OSHA: Occupational Safety and Health Administration
PEL-TWA: permissible exposure limit–time-weighted average—concentration not to be exceeded during
any 8-h workshift of a 40-h workweek
C: ceiling limit—ceiling concentrations must not be exceeded during any part of the workday; if instantaneous
monitoring is not feasible, the ceiling must be assessed as a 15-min TWA exposure
USEPA Integrated Risk Information System (IRIS database)
Categories for carcinogenic potential:
A Known Human Carcinogen
B1 Probable Human Carcinogen (based on human data)
B2 Probable Human Carcinogen (based on animal data)
C Possible Human Carcinogen
D Not Classifiable as to Human Carcinogenicity (based on lack of data concerning carcinogenicity in
humans or animals)
have direct applicability in industrial settings. They can be acquired directly from USEPA on databases
such as the Integrated Risk Information System (IRIS).
Absorption, Distribution, and Excretion
Most commonly, due to the characteristic of volatility, solvent exposure occurs via the inhalation route,
but there also may be absorption through the skin following exposures to vapors or through direct
contact with the liquid form. While penetration of solvent vapors through the skin typically is
considered to be negligible at low air concentrations, ACGIH and OSHA specifically note for a number
of substances that this route may be significant, hence the “skin” designation in occupational
guidelines. This is particularly true in cases where high concentrations exist in confined spaces and
where respiratory protection (e.g., use of air-purifying or air-supplied respirators) limits the potential
for inhalation exposure. As an example, it has been demonstrated that exposure to vapor of 2-butoxyethanol,
a glycol ether, under some conditions may result in uptake through the skin which exceeds
uptake via inhalation.
Characteristic of all volatile materials, the quantity of solvent that is absorbed by the lungs is
dependent on several factors, including pulmonary ventilation rate, depth of respirations, and pulmonary
circulation rate, all of which are influenced by workload. The partition coefficients that are
representative of solvent behavior in various tissues (i.e., for air:blood, fat:blood, brain:blood) are
specific to the chemical structure and properties of the individual solvent. Toluene, styrene, and acetone
are examples of rapidly absorbed solvents.