Eutrophication of surface water has increased significantly during the past decade, resulting in increased occurrences of toxic blooms. Cyanotoxins have become a global health threat to humans, wild animals, or domestic livestock. Hepatotoxic microcystins (MC) are the predominant cyanotoxins, which accumulate in aquatic organisms and are transferred to higher trophic levels. This is an issue of major concern in aquatic toxicology, as it involves the risk for human exposure through the consumption of contaminated fish and other aquatic organisms. The persistence and detoxification of MC in aquatic organisms are important issues for public health and fishery economics. Bioaccumulation of MC depends on the toxicity of the strains, mode of feeding, and detoxication mechanisms. Although mussels, as sessile filter feeders, seem to be organisms that ingest more MC, other molluscs like gastropods, as well as zooplankton and fish, may also retain average similar levels of toxins. Edible animals such as some species of molluscs, crustaceans, and fish present different risk because toxins accumulate in muscle at low levels. Carnivorous fish seem to accumulate high MC concentrations compared to phytophagous or omnivorous fish. This review summarizes the existing data on the distribution and dynamics of MC in contaminated aquatic organisms.

Oxygen consumption by Daphnia magna Straus was investigated as a bioindicator for the presence of 11 common aquatic pollutants: Benzo[b]fluoranthene (BbF), mercury(II) chloride (HgCl2), 2-dimethoxyphosphinothioylthio-N-methylacetamide (dimethoate), hexachlorocyclohexane (lindane), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 4-chloro-o-tolyloxy-acetic acid, bis(tributyltin) oxide (TBTO), carbon tetrachloride (CCl4), tetramethylthiuram disulfide (thiram), 2,4,6-trichlorophenol, and arsenic trioxide (As2O3). The measurement of oxygen consumption by D. magna was carried out after 15 and 210 min of exposure to the toxicants under controlled laboratory conditions. The technique applied in the present study was found to be useful for the detection of significant changes in oxygen consumption for most toxicants, with the exception of BbF, dimethoate, and CCl4. Significant differences in oxygen consumption were noted, relative to the control treatments, for six of the compounds after only 15 min of exposure. For thiram and TBTO, statistically significant changes in oxygen consumption were recorded after 210 min of exposure. The present results suggest that the measurement of oxygen consumption by D. magna is a useful biomarker and could possibly be used as a biological early warning system for detecting pollutants in the aquatic environment.