Identification of oligosulfide odorous compounds and their source in the Lake of Galilee

The chemical source of objectionable odors that are emitted from the Lake of Galilee (Lake Kinneret) and the relationship to the lake algae were elucidated. The lake serves for recreation and as an operational water reservoir, supplying a quarter of the water consumption of Israel. Analysis by closed loop stripping apparatus (CLSA), coupled with GC/MSD, olfactory GC and other detectors, revealed that the odorous compounds belong to the methylsulfide family, including, dimethylsulfide, dimethyldisulfide, dimethyltrisulfide and methyl methanethiosulfonate. The odor episodes coincide with a bloom of Peridinium gatunense algae. Peridinium gatunense rich samples, taken from the lake during the bloom season, emitted the same sulfur compounds. Depth profiles of Peridinium algae, sulfur compounds, dissolved oxygen, pH and temperature revealed strong correlation between the algal photo-induced motion in the water column and the distribution of dimethyldisulfide and dimethyltrisulfide, while the concentrations of dimethylsulfide and methyl methanethiosulfonate did not follow the same trend. In all cases, the dimethyloligosulfides were produced in the oxic region and were independent of the anoxic conditions in the hypolimniumon or in the sediment.