Influences of phosphate and silicate on Cr(VI) and Se(IV) accumulation in marine phytoplankton

The influences of major nutrient additions (P, Si, or N) on the accumulation of chromate [Cr(VI)] and selenite [Se(IV)] in three species of marine phytoplankton, including two diatoms (Thalassiosira pseudonana, and Skeletonema costatum), and one green alga (Chlorella autotrophica) were examined. Accumulation rate was quantified by measurements of metal concentration factor in algal cells over a short 5-h exposure period. Our results suggested that Se(IV) was little bioavailable to C. autotrophica and S. costatum, but was highly bioavailable to diatom T. pseudonana. Se(IV) accumulation in both diatoms and green alga was inversely dependent on the ambient P and Si concentration. Concentration factor decreased by 2.4-8.1 and 1.5-4.6 times with the additions of 7.2 microM P or 105.6 microM Si, respectively, after 5 h of exposure. Bioconcentration factors of Se(IV) in these species determined under laboratory conditions, which generally employ high nutrient concentrations, may not be applicable to those prevailing in the field. In contrast to Se(IV), Cr(VI) accumulation in the green alga and two diatoms was not related to the ambient P concentrations, but was inversely dependent on the ambient Si concentrations. These data demonstrated that the influences of major nutrients on anionic metal accumulation were highly species-specific, both for metals and phytoplankton. Nutrient enrichments in many water bodies may potentially affect the accumulation of anionic metals, and thus their biological transport and fate in these environments.