In the present study a new method has been developed and validated for detecting free microcystins (MCs) (MC-RR, MC-LR and MC-YR) by liquid chromatography-mass spectrometry (LC-MS) in the cyprinid Tinca tinca and in the crayfish Procambarus clarkii collected from three ponds in Extremadura (Spain) where the presence of the cyanobacteria species Microcystis aeruginosa and Anabaena spiroides has been confirmed. Once the method had been validated, free MCs were determined in fish (tench, T. tinca) and crayfish from different ponds in order to understand how they are bioaccumulated through the food web. MCs were not detected in any of the fish samples analyzed. It was confirmed that P. clarkii accumulated MCs in their tissues without losing their organoleptic characteristics, with MC-LR (2.3-18.1 μg MC-LR/g body weight) being the predominant MC variant detected in all the crayfish samples. MC-RR was measured in 50% of the samples analyzed, ranging between 1.4 and 7.8 μg MC-RR/g body weight and no MC-YR was detected. The results indicated that crayfish can accumulate free MCs in higher quantities than tench that live in ponds contaminated by toxic cyanobacteria species, and emphasized the need for regular monitoring if the health risks associated with their consumption are to be avoided.
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