Accumulation of Microcystin (LR, RR and YR) in Three Freshwater Bivalves in Microcystis aeruginosa Bloom Using Dual Isotope Tracer

Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodiana, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using C-13 and N-15 dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 mu g.L-1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at early 2 or 3 times higher than in S. woodiana and S. arcaeformis. In addition, the incorporated C-13 and N-15 atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated C-13 and N-15 atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. woodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.