The occurrence of heavy cyanobacterial blooms in eutrophic fresh waters has been a worldwide problem. Microcystins (MCs) produced by cyanobacteria are potent hepatotoxins.This study mainly contains two parts, ecological and toxicological studies of MCs.
The first part was a field survey of MCs in Gonghu Bay of Taihu in China from Jan. 2008 to Dec.2008. Seasonal variations of intracellular MCs and extracellular MCs were studied with disucssion on the possible effects of physico-chemical and biological factors underlying these variations. Water temperature was an important factor in determining cyanobacterial biomass and toxin production. During the study period, higher MCs concentration was found in summer and autumn, and Microcystis biomass and MCs concentrations reached peaks in October. Among the sampling-sites in Gonghu Bay, MCs concentration was higher in the water areas with less fluidity. Microcystis biomass, intracellular and extracellular MCs were significantly correlated with water temperature, suggesting that breakout of water bloom was closely related with temperature. There were significant correlations among N or P concentrations, Microcystis biomass and MCs content, suggesting that N and P levels affected MCs production through influencing Microcystis biomass. In Gonghu Bay, the maximum MCs concentration reached as high as 17μg/L MC-LR and was considerably higher than the drinking water safety standard recommended by WHO. So it is urgently needed to monitor MC pollution in Lake Taihu and to reduce the exposure risk of cyanobacterial toxins to both aquatic animals and human beings.
The second part was a laboratory study on distribution and deputation patterns of MCs in various tissues of Wistar rats via intravenous injection with discussion on the possible mechanisms underlying these patterns. Rats were injected intravenously (i.v.) with extracted MCs at a dose of 80 μg MC-LRequivalent/kg body weight. Free MCs concentrations in various tissues were detected at 1, 2, 4, 6, 12 and 24 h post-injection using liquid chromatography–mass spectrometry (LC–MS). MCs entered into the circulatory system rapidly after intravenous injection, and were transported to various organs, which subsequently resulted in different levels of MCs in various tissues. The highest concentration of MCs was found in kidney (0.034–0.295 mg/g dry weight), followed by lung (0.007–0.067 mg/g dry weight), stomach (0.010–0.058 mg/g dry weight) and liver (0.003–0.052 mg/g dry weight). MCs concentration was higher in kidney than in liver during the experiment, and two peaks of MCs concentration (at 2 and 24 h, respectively) were observed in kidney, indicating that MCs can be excreted directly via kidney of rat. Rapid accumulation and degradation of MCs were found in liver of the rats. It was difficult for MCs to be eliminated from gonad, hence MCs may cause chronic toxicity in the reproductive system.Though heart,intestine, spleen, brain and stomach contained less than 0.2% of injected MCs during the whole experiment stage, the presence of MCs in these tissues represents potential damage to them.