Surface microlayer reactions

Another mechanism for the removal of surface films was discovered by Wheeler (1972), who found that fatty acid films on seawater collapsed to form particles when exposed to near-ultraviolet radiation. The results indicated that there was an introduction of hydroperoxide groups into the parent fatty acid molecule with resultant polymerization of the products. Instead of polymerization, Timmons (1962) found that the constituents of plankton oil films were converted to smaller and more soluble fragments when exposed to artificial sunlight. Photochemically initiated solubilization appears to be a process common to some constituents of crude oil and fuel oil films as well, with low molecular weight acids, sulfoxides, and peroxides comprising some of the product soluble fraction (Burwood and Speers, 1974 Hansen, 1975 Larson et al., 1977). The rate of photo-oxidation of films of various fractions of crude oil spread on water was greatly increased 

The naphthalene derivatives apparently acted as photosensitizers which caused an increase in solubilization of the films through a reaction mechanism involving the formation of peroxides and alcohols. A case was made for the addition of photosensitizers to oil spills at sea to accelerate their removal by sunlight photo-oxidation, but in view of the observed toxicity of photoproducts from oil layer degradation towards aquatic microorganisms (Lacaze and Villedon, 1976 Larson et al., 1977), this approach warrants careful consideration. The use of chemical dispersants was found to magnify the toxicity by a factor of at least 10—15 (Lacaze and Villedon, 

Although metals such as the alkaline earth group should not promote photo-oxidative processes via CTTM transitions, they have been implicated in the photodecomposition of pteridines in seawater (Landymore and Antia, 1978). This has been explained through a structural modification of 

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I does not appear to be oxidized to I03 to any significant degree in the ohotic zone or the surface microlayer by chemical reactions. However, iodide oxidation may occur by biological mechanisms as found with macroalgae (3). Kennedy and Elderfield (36, 37) provide evidence for iodide oxidation (presumably bacterial) in sediments, but biologically mediated oxidation has not been shown yet as a significant process in the photic zone. 

Because 03 does not penetrate the ocean microlayer from the atmosphere, its reactions are significant only in the microlayer. The reaction of iodide with ozone has been documented at the surface microlayer of the ocean... 

Surface microlayers are Implicated in many chemical processes. They are exposed to the full solar spectrum of light arriving at the surface, and are often Inqiortant In photochemlcally mediated reactions. The microlayer, associated with most natural waters. Is considerably different In chemical composition from the underlying water column (26). Hence, the photochemlcally mediated reactions that take place In this layer may differ substantially from those In the water column. The differences In the reactions may be one of kinetics (rates of the reaction), or maybe mechanistic In nature and the reactlon(s) proceed(s) via different pathways resulting In different reaction products. 

Nevertheless, this small fraction of e or H transfer reactions could be a significant source of free radicals In the environment. Futhermore, flavins, because of their biological source and limited water solubility, could function more efficiently via e or H transfer reactions in substrate enriched micro-environments such as on particles, micro-organisms or In the sea surface microlayer. 

Effects of microlayer constituents or other surface-active agents on photochemical reactions in aqueous media have not been widely studied. Zadelis and Simmons (1983) demonstrated that the photodecomposition of naphthalene in Lake Michigan microlayer material was slower by a factor of about 2 relative to that in lake water. Larson and Rounds (1987) also showed that a 30 mM concentration of a surface-active material (sodium dodecyl sulfate) significantly decreased the photolysis rate of 1-naphthol at pH 7. In contrast, Epling et al. (1988) showed that borohydride-promoted photodechlorination of polychlorinated biphenyls was significantly increased in the presence of ca. 100 mM concentrations of the surface-active agents Brij-58 (a polyethoxyethanol) and sodium dioctyl succinate. The mechanisms for these observed rate effects are unknown. 

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