Ethylene and ethane production in an estuarine river: formation from the decomposition of polyunsaturated fatty acids

Abstract

Ethylene and ethane concentration in an estuarine river (Georgia, USA) averaged 0.5 nM and 0.03 nM, respectively. Exposure of this water to sunlight for 8 h resulted in concentrations of ethylene and ethane increasing to 1.6 nM and 0.07 nM, respectively. Dark production of ethylene and ethane was very slow, with detectable increases occurring only after 24 h. Filtration (0.2 μm) of estuarine water before sunlight exposure reduced ethylene production four-fold; this finding indicates the importance of particulates in the production of ethylene. Previous work showed that diatoms can produce ethylene. Ethylene and ethane are among the products of the photo-decomposition of particulate and dissolved polyunsaturated fatty acids. Linolenic acid added to sunlit estuarine water resulted in the production of both ethylene and ethane. When estuarine water was sterilized before sunlight exposure, the concentrations of ethylene and ethane reached 4.3 nM and 0.09 nM, respectively. This increase in sterilized estuarine water was probably due to the decomposition of cellular polyunsaturated fatty acids, which are no longer protected against photolysis by protective enzyme systems found in living cells. We suggest that the ethylene produced in estuarine water is produced biotically by phytoplankton and abiotically by the photolysis of polyunsaturated lipids in particulate and dissolved organic matter. High concentrations of ethylene are predicted to be produced in areas with high primary productivity.