The uptake and accumulation of Microcystin-RR (MC-RR) in fish was investigated under laboratory conditions and in wild fish. Jenynsia multidentata and Corydoras paleatus were exposed for 24h to 50 ug.L-1 MC-RR dissolved in water. After exposure, liver, gill, brain, intestine, gall bladder, blood and muscle were analyzed for MC-RR by HPLC and confirmed by LC-ESI-TOF-MS spectrometry. Furthermore, wild individuals of Odontesthes bonariensis were sampled from the eutrophic, cyanobacteria-containing San Roque reservoir, and analyzed for the presence of MC-RR in liver, gill, intestine, and muscle.
MC-RR was found in liver, gills, and muscle of all exposed and wild fish, while in Corydoras paleatus MC-RR was also present in the intestine. Moreover, we found presence of MC-RR in brain of Jenynsia multidentata. Results indicate that MC-RR uptake might occur at two different organs: intestine and gills, through either feeding (including drinking) or respiratory activities. This suggests that MC-RR is taken into the blood stream after absorption, and distributed to different tissue. The liver showed the major bioaccumulation of MC-RR in both experimentally exposed and wild individuals, while muscle of wild fish showed relative high amounts of this toxin in comparison with those exposed in the laboratory; tough MC-RR was present in muscle of fish exposed for 24 h. The amount of MC-RR in muscle of O. bonariensis exceeded the value suggested by WHO to be safe, thus causing a health risk to persons consuming fish as a result of chronic exposure to microcystin. Gills also showed bioaccumulation of MC-RR, raising questions on the mechanism involved in the possible uptake of MC-RR, raising questions on the mechanism involved in the possible uptake of MC-RR through gills as well as on its accumulation in this organ. Although MC-LR has been reported in brain of fish, this is the first report confirming the presence of MC-RR in this organ, which means that both toxins are able to cross the blood-brain barrier. These findings also raise questions on the probable neurotoxicity of Microcystins.
