PSP detoxification kinetics in the mussel Mytilus galloprovincialis. One- and two-compartment models and the effect of some environmental variables

Abstract

Paralytic shellfish poisoning (PSP) toxins are accunlulated by bivalves during toxic plankton blooms. In these bivalves the toxins are distributed into different body tissues which have varying affinities for them, and later these toxins are transferred by the bivalves to other trophic levels. After the disappearance of the toxic cells, shellfish remain tox~c for a vanable period of time, depending on the detoxification kinetics. We studied these kinetics in mussels Mytilus galloprov~ncialis previously exposed to a bloom of the PSP producing dinoflagellate Gymnodinium catenatum The toxin profile observed in the mussels was very similar to that of G. catenatum, showing that toxin transformations (chemical or enzymatic) had little or no importance in this case. The detoxification rates at all the sampling points decreased progressively from ca 0.25 to 0 d-' following a n inverse hyperboliclike curve. These rates were related to different degrees to the environmental factors studied (salinity, temperature, and light transmission as a measure of seston volume, and in vivo fluorescence as a measure of phytoplankton concentration) and to fresh body weight during each sampling period (estimated by multiple regression). In general, detoxification rates became increasingly independent of the variables cited as the experiment progressed. One-and 2-compartment detoxification models, both with 2 variants (with fixed and variable detoxification rates depending on the environmental variables and body we~ght), were used to describe the detoxification kinetics observed. Neither of the 2 variants of the l-compartment models correctly described detoxification. The 2-compartment models, on the other hand, particularly the environmentally controlled variant, fit the observed detoxification kinetics very well. There was only a slight difference between these last 2 models, which would suggest that the actual effect of the environmental variables considered in the detoxification process is unimportant.

Okadaic acid depuration in the mussel Mytilus galloprovincialis:one- and two-compartment models and the effect of environmental conditions

“…The observations made by Sampayo et al (1990) in several DSP episodes produced by Dinophysis spp, on the Portuguese coast suggest that depuration rates increase with phytoplankton concentration and also that, when the contribution of DSP producing species to the total phytoplankton bioinass is low, the contamination of mussels is slower than when it is high. As in the case of PSP toxins (Blanco et al 1997), we believe that phytoplankton concentration affects the process of depuration by increasing the digestive activity, which also leads to an increase in the metabolic fecal losses, thereby probably flushing out the bound toxins. These kinds of losses are made up mainly of remains of cells from the digestive gland tubules (Hawkins et al 1990) which presumably had accumulated toxins and, in this way, are eliminated.…”

“…The 2-compartment model, on the other hand, fit the first depuration point in each data set better. In our opinion the l-compartment model that includes the environmental variables and body weight is more realistic than the 2-compartment model because its main drawback, the poor fitting of the first point of each data set, (1) coincides with an atypically low okadaic acid concentration for these points followed by similar or higher toxin contents on the next sampling date, and (2) seems to be derived from one or several unknown factors which were not monitored during the experiment, as it showed a pattern in which the deviation of the model was larger in the bottom (8 m) than in the surface samples (3 m) and followed the same station order at each depth, and also because DSP analyses are carried out on the digestive gland, and therefore the second compartment does not involve other organs and, thus, might comprise a smaller fraction of the analyzed biomass than in the case of PSP (Blanco et al 1997). …”

“…One-and two-compartment models, which have previously been used to descnbe PSP depuration kinetics (Blanco et al 1997), were also used in this study (Fig. 2).…”

“…Only for 2 out of the 8 sampling points was the final body weight lower than at the start, and these 2 points were also the ones with the greatest salinity oscillations during the period studied. A more detailed description of the environmental variables can be found in Blanco et al (1997).…”

“…In other cases (Croci et al 1994), a unique depuration rate appears to exist for the whole depuration period. As in the case of PSP (Paralytic Shellfish Poisoning) toxins, these 2 responses can be described by 2-and l-compartment models, respectively (Silvert & Cembella 1995, Blanco et al 1997. Blanco et al (1995) have shown that a very simple l-compartment Fig 1.…”