Biologically active compounds were detected in water blooms on Lake Ladoga for the first time. Screening for cytotoxicity and for trypsin and acetylcholinesterase inhibitors revealed a degree of inhibitory activity by the water bloom biomass, which indicates the presence of cyanobacterial toxins in Lake Ladoga. High performance liquid chromatography (HPLC) of extracts of selected samples from the lake demonstrated a rather high diversity of bioactive compounds including hepatotoxic cyclic peptides (microcystins), enzyme inhibitors (cytotoxins), and a series of unidentified substances. Thirteen toxins and protease inhibitors were identified by the HPLC. The toxins were most diverse in the most eutrophic southern part of the lake (up to 12 bioactive compounds). Chromatograms showed that planktopeptin BL dominated in most of the samples investigated, except those from Svir Bay, where mcyst-LR prevailed. The results obtained indicate anthropogenic eutrophication of Lake Ladoga and a decrease in water quality. This lake is used as the only source of drinking water for the city of St. Petersburg.
Lake Ladoga (the largest lake in Europe) was characterized by good water quality some decades ago . Now as a result of human impact, the saprobity and toxicity of water have changed, phytoplankton biomass has increased, and populations of many sensitive species have declined . Morphological deformities of invertebrates are observed in heavily polluted areas and toxic effects are commonly encountered in fishes . The ecological crisis of Lake Ladoga is caused by human activities in its drainage area . This area is characterized by a relatively high degree of industrialization and economic development . The adverse environmental effects appear to be spatially irregular, occurring mostly in isolated bays and near-shore areas, especially when thermal bars are present, but there is also evidence of general increase of nutrient concentrations in the entire lake . Urgent measures should be taken for restoration of Lake Ladoga ecosystem .
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