Algal off-flavors in reservoirs

Historically, the proliferation of certain naturally occurring algae and the musty and earthy odors and flavors they produce have try reduced the quality of drinking water in reservoirs around the world. These algae can similarly affect fish flavor because off-flavor compounds in water become concentrated in lipid-rich fish tissue. The only successful treatment for off-flavor water in reservoirs has been the application of copper sulphate crystals to algal beds. Biocontrol with filter-feeding fish is currently being examined in pond research and may hold promise. Off-flavor compounds in drinking water and fish flesh are detected by taste and odor testing or by gas chromatography. We have developed a low-cost rest for musty and earthy off-flavors based on colorimetric procedures and designed for use by fisheries and waterworks researchers and managers. The major compounds producing musty and earthy off-flavor, 2-methylisoborneol (MIB) and geosmin, are first extracted from a l-L water sample by solid-phase adsorbent. The solvent is combined with the color-producing compound in concentrated sulfuric acid. Color development is completed in 30 min for MIB and approximately 20 h for geosmin and read with color comparators or with a colorimeter. Concentrations in fish are similarly determined but require distillation in a microwave oven. The sensitivity level is 1 part per billion for a l-L sample.