| Abstrakt: |
AbstractCyanobacterial toxins are a serious water quality concern in productive water bodies worldwide. Microcystins (MCs), which are hepatotoxins, are prevalent in Canadian freshwaters while the occurrence of neurotoxins anatoxin-a, anatoxin-a(s) and saxitoxin appears to be much less common. Concentrations of microcystin-LR (MCLR), presumed to be the most common of the more than 70 MC analogues, are highly variable in phytoplankton assemblages of lakes and greatly influenced by phytoplankton species composition. The frequency of occurrence and concentrations of MC in lakes in western Canada tend to increase with lake trophic status as well as decreasing N:P ratio. Microcystins accumulate in the aquatic food web through feeding activities of invertebrates (i.e., filter-feeding by clams and grazing by zooplankton and gastropods). Eventual trophic transfer of MC to fish, and resulting mortalities have been documented. Human health may also be at risk. Conventional water treatment may adequately remove low MC concentrations from source water, but can fail to completely remove MCs when initial concentrations are high. To address human health concerns, Health Canada established a drinking water guideline of 1.5 μg/L of MCLR. More recently, it has been suggested that β/N-methylamino-L-alanine (BMAA), a non-protein amino acid produced by many species of cyanobacteria, may cause neuro-degenerative disease, thus representing a significant emerging health issue. |
