Handbook of Solvents - George Wypych - ChemTech - Ventech!

1316 Tilman Hahn, Konrad Botzenhart, Fritz Schweinsberg
20.1.1.2.1 Inhalation
Inhalation is the most common pathway of solvent absorption, especially at working sites.
The pulmonal absorption of solvents depends on the following parameters: 3-6
• Exposure (concentrations and concentration fluctuations in the ambient air,
exposure time, physical exertion). The alveolar concentration of solvents or the
difference between air and blood concentration levels determine the diffusion
process into alveolar blood vessels. Physical exertion influences lung parameters,
especially ventilation, and consequently alveolar and blood concentrations.
• Lung parameters (pulmonary and alveolar ventilation, pulmonary perfusion,
air-blood coefficient, blood-tissue coefficient). These coefficients describe the
amount of solvents which can diffuse. The blood-tissue partition coefficient
influences the tissue equilibrium concentrations. Solvents with stronger
hydrophobic properties (e.g., toluene) reach equilibrium more rapidly because of a
low tissue-blood coefficient. Intraindividual differences such as child/adult are also
of significance.
• Physicochemical characteristics of solvents (solubility such as hydrophobic and
hydrophilic properties, state such as liquid or gaseous and degree of volatility).
20.1.1.2.2 Dermal uptake
Dermal uptake of solvents requires skin contact and depends on the area of contact, skin
thickness, dermal state (e.g., eczema and defects in the stratum corneum), exposure parameters
(contact time, etc.) and solvent properties. 7,8
The main barrier against percutaneous uptake of solvents are structures of the stratum
corneum, especially intercellular lipids and fibrous keratin. Removal of lipids by polar solvents
such as ethanol or hydration in the stratum corneum is associated with an increase of
skin permeability. Defects or lack of stratum corneum that may occur in skin diseases, at
particular skin locations such as hair follicles or glandula regions enhance the percutaneous
movement of solvents. The absorption through mucosa membranes is facilitated because of
the lack of the stratum corneum.
Skin defects or diseases can be provoked by solvents which cause irritation, cellular
hyperplasia and swelling, or removal of lipids. Skin defects are provoked mainly by frequent
use of solvents thus enhancing their absorption.
Other characteristics, which influence percutaneous absorption, are solvent concentration
gradients, solvent partitioning (water/lipid partition coefficient) and permeability
constants.
Lipophilic chemicals are absorbed most easily (for example, benzene). These can include
liquid solvents or solvents having low vapor pressure. 9-11 Vapors absorbed by dermal
uptake can significantly contribute to the body burden as a result of the whole body exposure:
e.g. 1-2 % of xylene or toluene, up to 5-10 % 1-methoxypropane-2-ol. 10 For other substances,
much higher skin absorption rates were measured after the whole body exposure:
2-methoxyethanol up to 55 %, 2-ethoxy-ethanol up to 42 %. 12
It is important to consider that the dermal uptake of vapors is especially significant
when using a gas-mask. 10 In addition to inhalation measurements, measurement of
percutaneous absorption is an important method for assessing health or environmental
risks.