Toxicology of Industrial Compounds

this allows a realistic evaluation of the risk when these compounds are
used.
Due to their economic importance, most studies have been carried out
with anionic surfactants. Fewer studies exist for the other classes of
surfactants. In vitro measurements of the percutaneous absorption of
sodium dodecyl sulphate indicated a low absorption value for rat skin as
well as for human skin (Blank and Gould, 1961; Embery and Dugard,
1969; Howes, 1975). The low cutaneous absorption of sodium dodecyl
sulphate could also be confirmed in experiments with rats (Greb, 1980).
After application of a 0.7 per cent aqueous solution of sodium dodecyl
sulphate (contact time 15 min), a cutaneous absorption of 0.26 µg cm −2
within 24 h was measured (Howes,1975).
In summarizing the results of the available studies, one can conclude that
only small amounts of surfactants are resorbed through the intact skin.
Since human skin in general is less permeable to chemicals (Rice, 1977;
Wester and Maibach, 1982), the amounts of surfactants absorbed
cutaneously in everyday use are probably even smaller. If the epidermis is
removed completely or partially, e.g. damaged skin, the degree of
absorption can increase substantially (Scala et al., 1968). In vitro studies
demonstrated that cationic surfactants are absorbed by the skin to a much
lesser extent than anionic surfactants (Scala et al., 1968; Geisler, 1976;
Faucher et al., 1979).
The degree of percutaneous absorption is generally larger for nonionic
surfactants than for anionic or cationic surfactants. Studies on the
percutaneous absorption of alkyl polyethyleneglycol ethers of the structure
C 12-(CH 2-CH 2-O) 3H, C 12-(CH 2-CH 2-O) 6H , C 12-(CH 2-CH 2-O) 10H, and
C 15-(CH 2-CH 2-O) 3H were performed under conditions of use (Black and
Howes, 1979). The aqueous solutions of the applied surfactants were
washed off after a contact time with the skin of 15 min. Under these
conditions, the penetration of the alkyl polyethyleneglycol ethers was
greater than the penetration of the analogous alcohol sulphates or alcohol
ether sulphates. The penetration increased with increasing length of the
carbon chain. Percutaneous absorption decreases for an ethylene oxide
content of 6 moles or more in the ethoxylate moiety.
Intestinal absorption, metabolism and excretion
W.STERZEL 347
The ingestion of surfactants is possible e.g. through the use of
surfactantcontaining toothpaste, through residues from dishwashing
detergents and through traces of surfactants in potable water. Anionic
surfactants are resorbed well in the intestine (Michael, 1968; Black and
Howes, 1980; Bartnik and Künstler, 1987). After absorption, a part of this
is excreted together with bile in the faeces and is subject to a enterohepatic
cycle. The majority of the absorbed surfactant is metabolized in the liver