I am undergoing renal dialysis treatment. Am I more at risk than others for exposure to cyanobacterial toxins?

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What are cyanobacteria and how could it affect you in you participate in renal dialysis?

Cyanobacteria is the scientific name for blue-green algae, or "pond scum." The first recognized species were blue-green in color, which is how the algae got their name. Species were identified since the range in color from olive-green to red. Cyanobacteria form in shallow, warm, slow-moving or still water. They are made up of cells, which can house poisons called cyanobacterial toxins. A mass of cyanobacteria in a body of water is called a bloom. When this mass rises to the surface of the water, it is known as surface scum or a surface water bloom. Although we don't know the extent to which cyanobacterial blooms occur across the US, we do know they mostly appear in the hot summer months and are quite prevalent in the prairies.

Just what are cyanobacterial toxins? Cyanobacterial toxins are the naturally produced poisons stored in the cells of certain species of cyanobacteria. These toxins fall into various categories. Some are known to attack the liver (hepatotoxins) or the nervous system (neurotoxins); others simply irritate the skin. These toxins are usually released into the water when the cells rupture or die. Health Canada scientists are more concerned about hepatotoxins than neurotoxins because neurotoxins are not considered to be as widespread as hepatotoxins in water supplies. Very few cyanobacterial toxins have actually been isolated and characterized to date. Better methods of detection are being developed to help us learn more about them, especially to find out which toxins are a problem and what conditions encourage their production.

While the proposed level of microcystins allowed for drinking purposes will not adversely affect the health of most people, patients undergoing renal dialysis treatment may be more susceptible to the associated health risks. Because dialysis patients receive dialysis two or three times per week (exposure to more than 300L of water per week), there is potential for dialysis patients to be exposed to elevated levels of these toxins.

Conventional surface water treatment processes are usually effective in removing the algal cells but are not very effective at removing or destroying dissolved toxins, particularly from supplies that contain high levels of organic material. Specialized surface water treatment processes can reduce the toxin levels to below the drinking water guideline, but these levels are still of concern for dialysis patients.

Most municipal water treatment plants do not regularly look for cyanobacterial toxins in the water supply. However, because cyanobacteria have strong smells and tastes and interfere with certain water treatment processes, most municipalities with a history of blooms monitor their surface water supplies for cyanobacteria. Once cyanobacteria are detected in the water supply, treatment plants can remove them in a number of ways. Conventional water treatment facilities can remove the cells by adding chemicals that bind them together. As the cells clump together, they become heavier and fall to the bottom of the reservoir or tank, where they can be easily filtered out.

While this method will remove cells, it will not remove potentially harmful cyanobacterial toxins. These can be removed using certain oxidation procedures or activated charcoal. Further research in this area is required. Generally speaking, chemicals (such as copper sulfate) or any other treatment method that causes the cells to break down and release their toxins should not be used. The best way to avoid the problems associated with cyanobacterial blooms is to prevent blooms from forming. This can be done by reducing the input of nutrients, such as phosphates, into the water source or by mixing the water in a reservoir.

If you think your water supply comes from surface water, you or your dialysis treatment provider, should ask your local treatment plant if this source of water is prone to blue-green algae blooms. If, after contacting your source water supplier, you discover there may be microcystins in your water, sampling should be done to determine whether the toxins are in the dialysate (hospitals and treatment centers may already have additional treatment capacity in place to eliminate all toxins of this nature). Additional treatment of the water may be necessary. These treatments can range from granular activated carbon filtration followed by reverse osmosis to much more complex membrane filtration systems (e.g., ultrafiltration). The extent of additional treatment will depend entirely on the quality of the municipal water supply.

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