Ecological And Toxicological Studies On Microcystins

Microcystins are a kind of hepatotoxic cyanotoxin. This study mainly contains two parts, ecology and toxicology of microcystins.The first part is a field survey of microcystins in Lake Xingyun, a subtropical plateau lake in China. Seasonal variations of dissolved MC, MC in seston and algal blooms were studied, and the effects of physico-chemical and biological factors on MC dynamics were discussed to evaluate on the possible mechanisms underlying these variations. The results were summarized as follows:1. Correlation analysis suggested that the production of Microcystis in Lake Xingyun was correlated with N content (such as TN and TDN) and optimum temperature (between 20 and 25℃).2. Significant linear relationship between total MC (dissolved MC + MC in seston) and the product of MC in algal blooms and Microcystis biomass suggested that MC concentration is regulated by both the biomass of toxin-producing phytoplankton in the water column and the concentration of MC produced per unit mass of these phytoplankton, and that factors affecting MC production are not necessarily the same with those affecting the biomass of the toxin-producing phytoplankton.3. In Lake Xingyun, the maximum MC concentration reached as high as 42.12μg l^-1 during the warm season and was considerably higher than those of Microcystis blooms in other regions of the world. It is urgently needed to monitor MC pollution in Lake Xingyun and to reduce the exposure risk of cyanobacterial toxins to both aquatic animals and human beings.The second part is a laboratory study on tissue distribution and deputation of microcystins in bighead carp via intraperitoneal injection. The possible mechanisms underlying these patterns in comparison with other fishes of different feeding modes were also discussed. The results were summarized as follows:1. This is the first to report MC contents (by HPLC–MS) in various organs of warm–water planktivorous bighead carp via intraperitoneal injection with two different doses, 200 and 500μg MC-LReq.kg^-1 BW. The highest level of MC was found in the kidney (0.094 - 4.641μg g^-1 DW), followed by the gallbladder (0.328– 2.474μg g^-1 DW), intestine (0.014– 0.751μg g^-1 DW), muscle (0.008 - 0.106μg g^-1 DW) and spleen (0 - 0.017μg g^-1 DW).2. Our results suggested that the clearance of MC in gallbladder seems more difficult than other organs and kidney may have capacity to transport microcystin. Most MC-LR but a small quantity of MC-RR in the aquaria water and rather low MC-LR content in the intestine and other organs indicated that the intestine of bighead carp can severely inhibit the transportation of MC-LR. It seems that elimination of MC-LR likely occurred at the intestine while MC-RR degraded in the liver after entering the blood system.