Concentrations of microcystin-derived compounds in Lake Erie sportfish

Background/Question/Methods

Lake Erie is an important economic and cultural resource, but it is threatened by recurring blooms of toxin-producing cyanobacteria. Microcystin, a potent liver toxin linked to human and animal illness and death, has been found in fish from Lake Erie, sometimes in excess of World Health Organization (WHO) guidelines for safe consumption. Despite this, few studies have analyzed the variation of microcystin concentrations in fish within Lake Erie, and these past studies have derived conflicting results as to the risk posed to public health. This is likely because of the extremely variable nature of the algae blooms from year to year, and because of the different species on which each study focused.

To help address this gap in knowledge, in the summer of 2013 we gathered large samples of three of the most commonly harvested sportfish in Lake Erie: Walleye (n>35), Yellow Perch (n>20), and White Perch (n>50). Edible portions of these fish were extracted and the toxin content evaluated by ELISA; toxin content was related to bloom intensity at the time of collection.  Samples that tested positive were further evaluated by LC-MS.

Results/Conclusions

Different fish species accumulated significantly different amounts of toxin (Walleye > White Perch > Yellow Perch).  Toxin in Yellow Perch was negligible in most samples.  Toxin concentrations in White Perch were moderate, but  most samples were below the WHO established threshold for safe public consumption, for appropriate consumption rates.  Toxin conceptrations in most Walleye samples were below this threshold at Ohio Department of Health advised levels of consumption, but above this threshold at higher, historically observed consumption rates.  Toxin in White Perch showed a small, but significant, positive correlation with bloom intensity during the time in which the fish were caught.  Fish size and age was not significantly correlated with toxin concentrations.  While compounds containing a functional group unique to microcystins and nodularins were identified by ELISA, further characterization by LC-MS yielded no results.  This implies that the toxins are not present in the parent form, and may be modified either in vivo in the fish or by the extraction procedure.