Adsorption of different types of dissolved organic matter to marine phytoplankton and implications for phytoplankton growth and Pb bioavailability

Adsorption of dissolved organic matter (DOM) to two species of marine phytoplankton (Isochrysis galbana and Thalassiosira weissflogii) was evaluated and quantified, and effects of DOM on the growth rate and Pb bioavailability were tested for I. galbana and compared with T. weissflogii. Isochrysis galbana growth rate was stimulated by different types of DOM. Humic acids (HA) had the highest stimulatory effect on cell growth followed by Suwannee river dissolved organic matter (SRDOM) and fulvic acids (FA). DOM also enhanced Pb adsorption and internalization by I. galbana, and the magnitude of these effects followed the same order: HA > SRDOM-FA, which was also the same order observed for the magnitude of DOM adsorption to surfaces. It is hypothesized that DOM adsorption on membrane surfaces may be a necessary step to cause both the increase in growth rate and the increase in Pb internalization by the algae, effects not observed in the case of the diatom T. weissflogii, an organism with an outer silica wall, thought to be the primary site of DOM adsorption. The different degree of effects caused by the different types of DOM may be explained according to their physicochemical properties.