Abstract
Microcystins (MCs) are the most frequently found cyanobacterial toxins in freshwater systems. Many MC variants have been identified and variants differ in their toxicity. Recent studies showed that the variants MC-LW and MC-LF might be more toxic than MC-LR, the variant that is most abundant and mostly used for risk assessments. As little is known about the presence of these two variants in The Netherlands, we determined their occurrence by analyzing 88 water samples and 10 scum samples for eight MC variants ((dm-7-)MC-RR, MC-YR, (dm-7-)MC-LR, MC-LY, MC-LW and MC-LF) by liquid chromatography with tandem mass spectrometry detection. All analyzed MC variants were detected, and MC-LW and/or MC-LF were present in 32% of the MC containing water samples. When MC-LW and MC-LF were present, they contributed to nearly 10% of the total MC concentrations, but due to their suspected high toxicity, their average contribution to the total MC toxicity was estimated to be at least 45%. Given the frequent occurrence and possible high toxicity of MC-LW and MC-LF, it seems better to base health risk assessments on the toxicity contributions of different MC variants than on MC-LR concentrations alone.
Highlights
The incidence and intensity of cyanobacterial blooms are on the rise worldwide [1,2]
Y resulting in the variants MC-RR, MC-LR, MC-LW and MC-LF Xif= positions R1 Yand
Recently we showed that considerable amounts of the variants MC-LW and MC-LF were present in cyanobacterial material from a case of dog fatalities in The Netherlands [25]
Summary
The incidence and intensity of cyanobacterial blooms are on the rise worldwide [1,2]. Cyanobacterial blooms present a serious health threat because cyanobacteria might produce potent toxins [3] of which microcystins (MCs) are most frequently encountered in freshwater blooms all around the world [4]. MCs are non-ribosomally synthesized cyclic heptapeptides with a size between and 1115 Da [4,5]. Their general structure is cyclo(-D-ala-L-X-erythro-β-D-methylaspartic acid-L-Y-Adda-D-isoglutamic acid-N-methyldehydroalanine), where Adda is (2S,3S,8S,9S)-3-amino-9methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid and X and Y are variable L-amino acids [6] (Figure 1). Y resulting in the variants MC-RR, MC-LR, MC-LW and MC-LF Xif= positions R1 Yand R2 NH2 CH3
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