10. Lipids in Water-Surface Microlayers and Foams
251
Foam formed in the tidal channels and at the edge of the water during rising
tides in the Bay of Fundy showed a high lipid content (made up mainly of
triacylglycerols, phospholipids, sterols, hydrocarbons, and pigments), typically at
a concentration of 65 mg . L - 1 (Napolitano et a!., 1992). The hydrocarbons
present in this foam consisted of a series of n-alkanes, from C-20 to C-39, with no
odd/even-chain length preference (CPI = 1.008), reflecting a very low level of
petroleum contamination.
10.6.2. Fatty Acids
Analysis of fatty acids in surface microlayers and foams is of special interest
because they provide information of sources and sinks of organic matter in aquatic
systems and about the type of organisms involved in their production (see Napolitano, this volume). Furthermore, the abundance of saturated and polyunsaturated
fatty acids in a sample is an indicator of the relative contribution of detritus and
viable biomass, respectively (White, 1995).
Despite some anomalies in the chemical composition of surface waters, due to
highly localized processes, some generalizations about the distribution of fatty
acid types are valid. For example, the concentration of short-chain fatty acids in
subsurface waters is usually higher than in the microlayer (Garret, 1967). Shortchain fatty acids are displaced from the surface film by longer-chain species due
to the competitive/adsorptive process. Long-chain fatty acids are less watersoluble and more surface-active. Also, the concentration of polyunsaturated fatty
acids is typically lower at the surface microlayer due to photoxidation at the airwater interface (Armstrong et a!., 1966).
There are very few detailed analyses of fatty acids in foams or surface microlayers in fresh water. Table lOA compares available data on the fatty acid composition of surface microlayers and foams from freshwater and marine environments. The fatty acid composition of foam and surface waters from the different
environments obviously reflects unique chemical and biological processes occurring at each site, and therefore generalizations are difficult to make. It is interesting to observe, however, that in studies of both marine and freshwater samples,
saturated and monounsaturated fatty acids accounted for 80-90% of the total fatty
acids, and long-chain polyunsaturated fatty acids (PUFA; characteristic components of organismal aquatic lipids) were not detected. Although the surface microlayers from fresh water and marine waters lack or have only trace concentrations
of PUFA (Simoneit et a!., 1980), estuarine and marine foam has significant concentrations of 0)6 and 0)3 PUFA (Napolitano et a!., 1992; Marty and Choiniere,
1979).
In estuarine waters, the concentrations of saturated and monounsaturated fatty
acids in the lipids of the particulate fraction of the surface microlayers more
closely resemble those of the foam than those of the dissolved lipids in the
microlayer itself (Marty and Choiniere, 1979). These results suggest that particulate organic matter in the surface microlayer is effectively captured during the
process of foam formation. However, lipids in foams collected during a I-year
251
Foam formed in the tidal channels and at the edge of the water during rising
tides in the Bay of Fundy showed a high lipid content (made up mainly of
triacylglycerols, phospholipids, sterols, hydrocarbons, and pigments), typically at
a concentration of 65 mg . L - 1 (Napolitano et a!., 1992). The hydrocarbons
present in this foam consisted of a series of n-alkanes, from C-20 to C-39, with no
odd/even-chain length preference (CPI = 1.008), reflecting a very low level of
petroleum contamination.
10.6.2. Fatty Acids
Analysis of fatty acids in surface microlayers and foams is of special interest
because they provide information of sources and sinks of organic matter in aquatic
systems and about the type of organisms involved in their production (see Napolitano, this volume). Furthermore, the abundance of saturated and polyunsaturated
fatty acids in a sample is an indicator of the relative contribution of detritus and
viable biomass, respectively (White, 1995).
Despite some anomalies in the chemical composition of surface waters, due to
highly localized processes, some generalizations about the distribution of fatty
acid types are valid. For example, the concentration of short-chain fatty acids in
subsurface waters is usually higher than in the microlayer (Garret, 1967). Shortchain fatty acids are displaced from the surface film by longer-chain species due
to the competitive/adsorptive process. Long-chain fatty acids are less watersoluble and more surface-active. Also, the concentration of polyunsaturated fatty
acids is typically lower at the surface microlayer due to photoxidation at the airwater interface (Armstrong et a!., 1966).
There are very few detailed analyses of fatty acids in foams or surface microlayers in fresh water. Table lOA compares available data on the fatty acid composition of surface microlayers and foams from freshwater and marine environments. The fatty acid composition of foam and surface waters from the different
environments obviously reflects unique chemical and biological processes occurring at each site, and therefore generalizations are difficult to make. It is interesting to observe, however, that in studies of both marine and freshwater samples,
saturated and monounsaturated fatty acids accounted for 80-90% of the total fatty
acids, and long-chain polyunsaturated fatty acids (PUFA; characteristic components of organismal aquatic lipids) were not detected. Although the surface microlayers from fresh water and marine waters lack or have only trace concentrations
of PUFA (Simoneit et a!., 1980), estuarine and marine foam has significant concentrations of 0)6 and 0)3 PUFA (Napolitano et a!., 1992; Marty and Choiniere,
1979).
In estuarine waters, the concentrations of saturated and monounsaturated fatty
acids in the lipids of the particulate fraction of the surface microlayers more
closely resemble those of the foam than those of the dissolved lipids in the
microlayer itself (Marty and Choiniere, 1979). These results suggest that particulate organic matter in the surface microlayer is effectively captured during the
process of foam formation. However, lipids in foams collected during a I-year