Re: How do you test for the amount of cyanobacteria in water?

A few species of cyanobacteria can produce compounds that act as neurotoxins (damaging to nerves), hepatotoxins (damaging to liver cells), or enterotoxins (toxic to the intestine) in humans and animals. These toxins are usually associated with large blooms of cyanobacteria. There are many different kinds of cyanotoxins that have been identified, mainly from Microcystis and Oscillatoria species. The amount of cyanobacteria in a liquid sample can be determined roughly by measuring the absorbance of certain pigments (phycobilins) in a spectrophotometer. This will only work if the cyanobacteria are relatively abundant. My understanding of your project is that you wish to test and compare commercially available bottled waters. None of these will have enough cyanobacteria to measure spectrophotometrically. You might filter several hundred gallons and then examine the collected material, but this doesn't seem very practical for you. It is likely that the water has already been filtered during processing. It is unlikely that you will find significant numbers of cyanobacteria in these sources.

The level of cyanotoxins, if any will also be very low. You would need to extract and concentrate large volumes of water to detect these compounds. You would also need to use sophisticated chromatography equipment like HPLC (High Pressure Liquid Chromatography) or GC (Gas Chromatography). And remember that there are dozens of different cyanotoxins, each one requiring its own purification and identification scheme. I don't know of any easy way to test for cyanotoxins.

One approach that is popular in the wastewater industry is to use some kind of bioassay to measure toxicity. For example, Hach Company (800-227-4224) produces a kit called ToxTrack. Here bacteria are exposed to a potential toxic agent and then certain biochemical activities are measured. This will tell you if the water is toxic to the bacteria, but it does not identify the toxic agent. Also, it gives no indication if the toxic agent would be toxic for humans. You can also do growth measurements using serial dilutions of bacteria and lots of agar plates. Again, bacterial toxicity may have no relevance to human toxicity. Measurement of toxicity can be performed in rat or mouse model systems. Here you would maintain 5 mice on each of the waters being tested. Then the weight and vigor of the mice would be recorded over several weeks. This could also be done in metabolic cages for more information. At the end of the experiment, the mice are killed and their organs examined for gross changes and slices are made and stained for examination in the microscope. Not easily done by a novice.

It seems to me that bottled waters will be pure enough to make determination of their toxic effects difficult. Even measuring their chemical impurities may be difficult without sophisticated equipment. Although certain inorganics can be measured with kits and organic contents can be measured as biological or chemical oxygen demand. It still seems that these will be below the detection limit of the simple tests for these purified drinking waters.

Hope this helps.