Hepatotoxic Cyanobacterial Blooms in the Lakes of Northern Poland Joanna Mankiewicz, 1 Jarka Koma ´ rkova ´, 2 Katarzyna Izydorczyk, 1 Tomasz Jurczak, 3 Malgorzata Tarczynska, 3 Maciej Zalewski 1,3 1 International Centre for Ecology, PAS, 3 Tylna, 90-364 Lodz, Poland 2 University of South Bohemia, 31 Branis ˇ ovska ´ , Cz-37005 C ˇ eske ´ Bude ˇ jovice, Czech Republic 3 Department of Applied Ecology, University of Lodz, 12/16 Banacha, 90-237 Lodz, Poland Received 17 February 2005; revised 2 May 2005; accepted 9 May 2005 ABSTRACT: The lakes of northern Poland are among the recreational sites most valued by Polish and German holiday makers. Given the socioeconomic importance of these lakes, water quality should be maintained at high levels for such intensive recreational purposes. In 2002 studies of species composition, biomass, and toxin production by phytoplankton and the attendant physicochemical variables were per- formed in order to assess the risk of cyanobacterial blooms in selected northern lakes: Lakes Jeziorak, Jagodne, Szymoneckie, Szymon, Taltowisko, Siecino, and Trzesiecko. The research showed that total phosphorus (0.1 mg P/L) and total nitrogen (1.5 mg N/L) in the studied lakes almost exceeded the permis- sible limits for eutrophication of water bodies. Most phytoplankton samples were taken in late summer, when cyanobacteria were expected to reach their highest biomass. At the time of sampling most of the lakes were dominated by oscillatorialean and nostocalean species. Average chlorophyll-a concentration was higher than 10 g/L in almost all the lakes studied, which corresponded with an average microcystin concentration in the range of 4–5 g/L. The main microcystins in the analyzed samples were dmMC-RR, MC-RR, MC-YR, and MC-LR. The results demonstrated a potential for intensive cyanobacterial blooms to appear during the summer in northern Polish lakes. The levels of cyanobacteria found in the lakes investi- gated indicated that toxicity had reached the first-alert level according to World Health Organization rec- ommendations. If microcystin-producing cyanobacteria dominate, with a microcystin concentration of 2–4 g/L, symptoms of toxicity can appear in the swimmers most sensitive to exposure. Analysis of cya- nobacterial assemblages in northern Polish lakes also indicated a significant presence of Aphanizomenon species including a Scandinavian species, A. skujae (Skuja) Kom.-Legn. & Cronb. Future investigations of Polish lakes also should assess neurotoxins and study the biology of their producers. This study was the first attempt to evaluate the potential danger of toxic cyanobacterial blooms in the lakes of northern Poland. # 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 499–506, 2005. Keywords: cyanobacteria; phytoplankton; diversity; microcystin; recreational water; health risk; PPIA; HPLC INTRODUCTION Eutrophication of water bodies often leads to the formation of intensive cyanobacterial blooms (Carmichael, 1997; Chorus et al., 2000, 2001). This process is a result of incomplete sewage purification and increased agricultural  C 2005 Wiley Periodicals, Inc. 499 Correspondence to: J. Mankiewicz; e-mail: mankiew@biol.uni.lodz.pl Contract grant sponsor: MIDI-CHIP. Contract grant number: EVK2-CT1999-00026 and EVK2-2002-00546. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.20138