Depuration kinetics and persistence of the cyanobacterial toxin microcystin-LR in the freshwater bivalve Unio douglasiae.

We carried out uptake and depuration experiments in the laboratory to investigate the effects of temperature (15 degrees C and 25 degrees C) on the depuration kinetics and persistence of a cyanobacterial toxin, microcystin-LR (MCYST-LR), in a freshwater bivalve, Unio douglasiae. Bivalves were fed toxic Microcystis cells in the 15-day uptake experiment and nontoxic diatoms in the following 15-day depuration experiment. Each bivalve's hepatopancreas was lyophilized and extracted with a butanol:methanol:water solution for analysis of MCYST-LR by high-performance liquid chromatography. The toxin in the organ accumulated rapidly after the beginning of the uptake experiment and reached approximately steady-state conditions on day 5 at concentrations of 130 +/- 11 microg g(-1) dry weight at 15 degrees C and 250 +/- 40 microg g(-1) at 25 degrees C. In the depuration experiments MCYST-LR was eliminated asymptotically from the tissue. The values of the depuration rate constant (k(d)), calculated with a first-order one-compartment model, were found to be 0.142 +/- 0.044 day(-1) at 15 degrees C and 0.226 +/- 0.046 day(-1) at 25 degrees C. The depuration Q(10) value from 15 degrees C to 25 degrees C equaled 1.6. This study was the first to reveal the kinetics of depuration for MCYST-LR in a bivalve. The results show that MCYST-LR may be eliminated slowly in autumn and winter and persist in the tissue until spring. Thus, in terms of toxicokinetics, the risk to people of being poisoned by bivalves would increase if toxic blooms occur in autumn.