Sustainable and effective water management plans must have a reliable risk assessment strategies for harmful cyanobacterial blooms (HABs) that would enable timely decisions to be made, thus avoiding the trespassing of ecological thresholds, leading to the collapse of ecosystem structure and function. Such strategies are usually based on cyanobacterial biomass and/or on the monitoring of known toxins, which may, however, in many cases, under- or over-represent the actual toxicity of the HAB. Therefore, in this study, by the application of growth-inhibition assays using different bacteria, algae, zooplankton and fish species, we assessed the toxicological potential of two cyanobacterial blooms that differed in total cyanobacterial biomass, species composition and cyanopeptide profiles. We demonstrated that neither cyanobacterial community composition nor its relative abundance, nor indeed concentrations of known toxins reflected the potential risk of HAB based on growth-inhibition assays. We discuss our findings in the context of food-web dynamics and ecosystem management, and suggest that toxicological tests should constitute a key element in the routine monitoring of water bodies so as to prevent under-/over-estimation of potential HAB risk for both ecosystem and public health.

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Abstract. The main aims of the present study were: 1) to determine the concentration of Cd in water during the experiment after long-term exposure to rainbow trout embryos and larvae to sublethal concentrations of Cd-based quantum dots (QDs) and Cd chloride salt, and 2) to evaluate accumulation of Cd in the whole body of test-organisms depending on the type of chemical substances (QDs or single Cd) and the duration of exposure. Experimental studies at the early developmental stages of rainbow trout were performed under static conditions. Cd concentration in water during the experiment was significantly higher in QD solution than in CdCl2 solution, and it declined over time. A comparative analysis indicated that the Cd accumulation in testorganisms from QDs was mostly higher than that from CdCl2. The accumulation of Cd from QDs tends to increase with increasing duration of exposure. The bioconcentration factor for Cd increased in embryos and larvae over time until reaching the maximum at the end of the QD exposition.