Depth profiles of cyanobacterial hepatotoxins (microcystins)in three Turkish freshwater lakes

摘要

The Turkish freshwater lakes,Sapanca,Iznik and Taskisi(Calticak) have been enriched with nutrients from agriculture and domestic sources for many years.A major bloom of cyanobacteria(blue-green algae) in Lake Sapanca was recorded in May 1997,closely followed by a sish kill.Investigations were subsequently made on cyanobactria and water qualityof the lakes,including analysis for cyanobactrial hepatotoxins(microcystins) in the filteredparticulate fraction.Samples,taken from the beginning of May to end of August 1998,were analysed for microcystins by high-performance liquid chromatography with photodiode array detection (HPLC-PDA),protein phosphatase inhibition assay(PPIA) and an enzyme-linked immunosorbent assay(ELISA).No microcystins were detected in tehwater column in Lake Sapanca above 10 m,but toxins were found in filtered cyanobacterial samples from 20m depth at a concentration of 3.65 mug l~-1 microcystin-LR equivalents.Ninety percent of the microcystin pool detected in L.Sapanca was foudn between depths of 15 and 25 m.The principal microcystin detected by HPLC-PDA wwas imilar ot microcystin-RR.Two unidentfied microcystin variants were found in Lake Taskisi surfacesamples at a concentration of 2.43 mug l~-1 mcrocystin-LR equivalents in teh filtered ycanobacterials cell fraction.Althouth 10 water samples (10 X 51) were taken from Lake Iznik(surface to 20 m,5m intervals),no microcystins were detected by HPLC-PDA(limit of detection 10 ng).Thedepth at which microcystins were detected in L.Sapanca coincided with the draw-off depth for the drinking water supply for the city of Sakarya.