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

Following an episode of Diarrhetic Shellfish Poisoning (DSP) in mussels Myt ilus galloprovincialis from the Ria de Pontevedra (Galicia, NW Spain), prod uced by organisms of the genus Dinophysis (dinoflagellate), a batch of cont aminated mussels was transplanted to several uncontaminated sites having di fferent environmental conditions. The depuration kinetics of okadaic acid ( the dominant toxin involved in the episode) in each experimental mussel bat ch was monitored during a 70 d period, as were the corresponding salinity, temperature, fluorescence, light transmission and mussel body weight. Envir onmental conditions and body weight were shown to have an effect on depurat ion rates by principal component and multiple regression analysis. Although most of the variables studied showed a high degree of covariation, fluores cence and Light transmission, which serve to measure the availability of so lids and phytoplankton for mussels, appeared to have the most prominent eff ect on depuration. Four different models were tested in order to describe d epuration kinetics: 1- and 2-compartment models, each in 2 versions, with a nd without the inclusion of the effects of the 4 environmental variables st udied and body weight. The 1-compartment model without the complementary va riables did not give an appropriate description of the kinetics, but when t hese variables were included, the general fitting was good and a pattern wa s found in the most important deviations. The simplest of the 2-compartment models fitted also produced an output that adequately described the kineti cs observed. However, attempts to estimate the parameters of 2-compartment models including the complementary variables consistently produced a 1-comp artment model. The model chosen to describe depuration kinetics substantial ly influences the estimation of the effect of the environmental variables.