The objective of this study was to identify a possible effect of food on the acceleration
of decontamination in blue mussels, Mytilus edulis, containing diarrhetic
toxins belonging to the okadaic acid (OA) structural group. An experimental protocol was
designed to describe and compare the decontamination kinetics and detoxification rates of
naturally OA-contaminated mussels that had either received or not received food for three
weeks. The protocol was applied in two trials (in June 2006 and June 2007, called Ker06
and Ker07), conducted one year apart on samples of mussels collected in the same area, at
the same season. Okadaic acid (OA), the main lipophilic toxin produced by the toxic alga
Dinophysis acuminata, was analysed over the course of the
decontamination, in hydrolysed (total OA) and non hydrolysed (free OA) digestive gland
extracts, in order to estimate acyl-esters (7-O-acyl-ester derivatives of
OA) concentrations. OA analyses were also made for toxin presence in biodeposits and in
the aqueous phase. Bivalve physiological status was evaluated by biomass measurements (dry
weight of flesh) and two biochemical compounds (total lipid and glycogen concentrations).
Measured physiological parameters showed that mussels did not suffer under experimental
conditions. Both trials showed that the food accelerated the elimination of free and total
OA. This effect cannot be attributed to a dilution of the toxin in the tissue, as results
expressed in toxin burden led to the same conclusion. The kinetic models of
decontamination differed between the two experiments: the model was linear for Ker06,
provided that the values corresponding to the first two days were discarded, whereas data
fitted a decreasing exponential curve better in Ker07. Detoxification rates increased as
the food supply increased. After three weeks of experimentation, the detoxification rates
for total OA in Ker06 and Ker07 were 52 and 61%, respectively, in unfed mussels and 90 and
89% in fed mussels (with the highest level in Ker07). Comparisons between the free OA and
esters showed that detoxification rate was higher for free OA than for esters, whatever
the level of food supply. The results of this study suggest that food increase probably
accelerates elimination of OA and OA-esters but the latter are eliminated at a lower
speed.