254
G.E. Napolitano and D.S. Cicerone
Lipid markers are widely used in geochemical and ecological studies of freshwater and marine environment (see Napolitano, this volume). Although foam can
hold a diverse microbial community of bacteria. algae, and fungi, ecological
studies of this microenvironment are rare. Furthermore, the trophic structure of
foam could be far more complex due to the possible inclusion of neustonic
organisms commonly found in surface water (i.e .. rotifers, nematodes, microarthropods). The biomass, trophic interactions, and the physiological status of
these neustonic communities could be assessed by the analysis of lipid content
and lipid composition.
Although foams are a natural phenomenon, the sudden development foam
patches in lakes and streams may also be related to industrial operations and,
therefore, can raise serious regulatory and compliance concerns. Some government and industrial regulations require the reporting of the characteristic and the
origin of foam formations in lakes and streams near industrial sites. However, the
differences between natural and artificial foams are subtle, and they are based on
subjective criteria such as appearance. color, and texture (Valentine, Environmental Compliance, ORNL, U.S. Department of Energy, personal communication).
The presence of foam as result of a water pollution event is obviously associated
with the release of detergents or other potent surface active products. Therefore,
the definitive characterization of a particular foam as of natural or man-made
origin will require the isolation and identification of the contaminant surfactant.
This procedure may sometimes become time-consuming and expensive. The analysis of lipids in foam and surface microlayers has the potential to be used as an
alterative method to distinguish between natural and artificial foam. The proposed
method does not require the identification of the surfactants. Instead, it consists of
extracting the surface active compounds from the water by means of current
standard methods, their subsequent hydrolysis, and a chromatographic analysis of
their hydrophobic chains. Hypothetically. industrial surfactants would show a
relatively simple chromatographic profile, mainly consisting ofthe C- I 2 and C- 14
acyl or alkyl moieties normally used in the formulation of detergents and emulsifiers. Contrarily, biogenic surfactants would present a much wider spectrum of
acyl and alkyl moieties and the dominance of the C- I 6 and C-J8 fatty acids
typically present in natural lipids.
10.8. Final Remarks
In the preceding sections, we have shown that lipids, derived from the decay and
exudates of aquatic and terrestrial biota and from autochthonous neustonic populations, accumulate in the water-surface microlayer. We have defined the surface
microlayer as the top 30-100 f.Lm of the water column and showed how the
transport of material across this environment can be qualitatively described by the
stagnant boundary layer model (Whitman, 1923) and the surface renewal model
(Danckwerts, 1951; Higbie, 1935). Hydrophobic pollutants and metals are also
concentrated in the surface microlayer by the production of bubbles and other
transport agents, contributing to the load of organic and inorganic matter de-
G.E. Napolitano and D.S. Cicerone
Lipid markers are widely used in geochemical and ecological studies of freshwater and marine environment (see Napolitano, this volume). Although foam can
hold a diverse microbial community of bacteria. algae, and fungi, ecological
studies of this microenvironment are rare. Furthermore, the trophic structure of
foam could be far more complex due to the possible inclusion of neustonic
organisms commonly found in surface water (i.e .. rotifers, nematodes, microarthropods). The biomass, trophic interactions, and the physiological status of
these neustonic communities could be assessed by the analysis of lipid content
and lipid composition.
Although foams are a natural phenomenon, the sudden development foam
patches in lakes and streams may also be related to industrial operations and,
therefore, can raise serious regulatory and compliance concerns. Some government and industrial regulations require the reporting of the characteristic and the
origin of foam formations in lakes and streams near industrial sites. However, the
differences between natural and artificial foams are subtle, and they are based on
subjective criteria such as appearance. color, and texture (Valentine, Environmental Compliance, ORNL, U.S. Department of Energy, personal communication).
The presence of foam as result of a water pollution event is obviously associated
with the release of detergents or other potent surface active products. Therefore,
the definitive characterization of a particular foam as of natural or man-made
origin will require the isolation and identification of the contaminant surfactant.
This procedure may sometimes become time-consuming and expensive. The analysis of lipids in foam and surface microlayers has the potential to be used as an
alterative method to distinguish between natural and artificial foam. The proposed
method does not require the identification of the surfactants. Instead, it consists of
extracting the surface active compounds from the water by means of current
standard methods, their subsequent hydrolysis, and a chromatographic analysis of
their hydrophobic chains. Hypothetically. industrial surfactants would show a
relatively simple chromatographic profile, mainly consisting ofthe C- I 2 and C- 14
acyl or alkyl moieties normally used in the formulation of detergents and emulsifiers. Contrarily, biogenic surfactants would present a much wider spectrum of
acyl and alkyl moieties and the dominance of the C- I 6 and C-J8 fatty acids
typically present in natural lipids.
10.8. Final Remarks
In the preceding sections, we have shown that lipids, derived from the decay and
exudates of aquatic and terrestrial biota and from autochthonous neustonic populations, accumulate in the water-surface microlayer. We have defined the surface
microlayer as the top 30-100 f.Lm of the water column and showed how the
transport of material across this environment can be qualitatively described by the
stagnant boundary layer model (Whitman, 1923) and the surface renewal model
(Danckwerts, 1951; Higbie, 1935). Hydrophobic pollutants and metals are also
concentrated in the surface microlayer by the production of bubbles and other
transport agents, contributing to the load of organic and inorganic matter de-