Environmental Engineering Reference
In-Depth Information
those for anionic formulations are 1 to 50 ppm. These values are much less than
the corresponding cmc values, indicating that aquatic toxicity stems from a
surfactant monomer. Nonionic surfactants are mostly less toxic than the ionic and
alkylphenoxy ethoxylates are generally less toxic than their degradates, nonyl and
octylphenols. The toxicity of nonionic surfactants to both aquatic and terrestrial
organisms has been reviewed by Krogh et al. (2003). Their effects on various
biological activities are considered to originate from interactions with bioactive
macromolecules such as proteins, peptides, amino acids, and membrane
phospholipids (Cserháti 1995). Nonionic surfactants are known to bind readily to
various proteins and membranes, which alters the protein structure and the
permeability of the membrane. Chattopadhyay et al. (2002) have demonstrated by
using various sequences in two-dimensional 1 H- and 13 C-NMR that bovine heart
cytochrome c oxidase is stabilized by association with lauryl maltoside via inter-
action of its polar head group with the protein surface. The fluidity of the plasma
membrane of corn roots was found to change with the concentration of nonionic
surfactant Brij-58 by fluorescence depolarization techniques (Behzadipour et al.
2001). Either the decrease in maximum buildup of a membrane potential or the
enhanced decay of the potential in the chromatophores of Rhodobacter sphaeroides
by linear alcohol ethoxylates showed the nonspecific interactions of these
surfactants with the membrane and their effective concentration correlated well
with their biological toxicity (Müller et al. 1999).
The effect of surfactants on soil microbiology was studied in a sandy agricultural
soil by using polydisperse LAS (Elsgaard et al. 2001). Except for
-glucosidase
activity, all soil parameters including basal respiration and the content of phospholi-
pid fatty acids were found to be sensitive to LAS with EC 10 values from < 8 to
22 mg/kg of dry soil weight, which was likely to originate from interactions of LAS
with cell membranes.
Distribution of microorganisms in a water-sediment system is known to be
affected by the presence of some surfactants. By using sodium dodecyl sulfate
(SDS) and its homologues with different alkyl chains, Marchesi et al. (1991)
examined the population dynamics of both free-living and attached bacteria by
epifluorescence microscopy in a freshwater microcosm. Alkyl sulfates having decyl
or dodecyl chains that were adsorbed to sediments and bioavailable to bacteria were
found to cause the adhesion of bacteria to the sediment surface. Bacteria are known
to be attached on the surface of various solids, which is related to the hydrophobic-
ity of the cell wall being examined by the contact angle of water on cells (Van
Loosdrecht et al. 1987). Linear alcohol ethoxylates can alter this cell wall hydro-
phobicity, depending on the chain length in alkyl and polyethoxy moieties. The
longer the polyethoxy moiety, the less adhesion of Sphingomonas sp. strain
DGB01o onto solid (Brown and Jaffé 2006). When the alkyl chain was elongated,
higher adhesion was observed. The alteration of cell wall hydrophobicity was found
to be also dependent on bacterial strains from a biodegradation study of octadecane
by four Pseudomonas aeruginosa strains in the presence of rhamnolipid biosur-
factant (Zhang and Miller 1994).
β
Search WWH ::




Custom Search