Toxicology of Industrial Compounds

348 TOXICOLOGY OF SURFACTANTS
and the respective metabolites are eliminated in the urine. The metabolic
degradation of the linear alkyl chain is performed by -oxidation followed
by β-oxidation. The ether-linkage in the ethoxylate portion of sulphated
alcohol ethoxylates seems to be resistant to metabolism.
Linear alkylbenzene sulphonates and branched alkylbenzene sulphonates
are metabolized to short chain sulphophenyl carboxylic acids. N-alkyl
sulphates are metabolized by -oxidation of the hydrophobic end followed
by β-oxidation. Butyric acid-4-sulphate and acetic acid-2-sulphate are the
end products, which are then further converted in small amounts nonenzymatically
to sulphate and -butyrolactone (Ottery et al., 1970). Studies
by Taylor et al. (1978) demonstrated that alkyl sulphonates are degraded
via the same pathway as alkyl sulphates.
Cationic surfactants can be assumed to be resorbed in the intestine only
to a small extent. This was confirmed in a study with trimethyl cetyl
ammonium bromide (Isomaa, 1975; Isomaa et al., 1976). Due to the low
level of resorbed surfactant, an unquestionable identification of the
metabolites was not possible. Parts of absorbed cationic surfactants were,
as found for anionic surfactants, excreted together with bile in the faeces
and to a lesser degree with the urine.
Nonionic surfactants are resorbed to a large degree in the intestine
(Drotman, 1980). A significant part of the material is eliminated with the
bile. Cleavage of the ether linkage is obviously possible. Homologous
ethyleneglycol ethers are probably generated as metabolites along with the
corresponding carboxylic acids which are formed through oxidation of the
terminal hydroxymethyl group (Drotman, 1980). The sorbitan fatty esters,
which are often used as emulsifiers, and the ethoxylated fatty acid esters
are hydrolysed in the gastrointestinal tract after oral administration
through cleavage of the ester bond. While the resulting fatty acid is treated
metabolically like a natural fatty acid, the polyol component of the
sorbitan fatty acid is absorbed in the intestine, but is not further oxidized
and is eliminated predominantly with the urine (Elworthy and Treon, 1967).
Systemic effects
Talking about systemic effects means, in contrast to local effects, the
description of reactions arising after the substance has entered the organism
after swallowing, skin penetration or inhalation. For surfactants,
resorption through the skin has to be considered in particular. As described
in the previous section, it is relatively small. But for products that
frequently come into close contact with the skin, either unintentionally or
due to their intended use, the resorption of very small amounts over a long
period of time cannot be prevented.