Bioaccumulation, subcellular distribution, and trophic transfer of copper in a coastal marine diatom

Cellular uptake and subcellular distribution of copper were measured in the coastal marine diatom Thalassiosira weissflogii grown with free Cu ion concentrations (10(-14.79)-10(-9.79) M) that are typical of coastal waters. Intracellular Cu quotas increased 2-3-fold and 4-5-fold per decade increase in free Cu ion concentration over the pCu (pCu = -log [CU(2+)]) ranges of 14.79-11.79 and 11.79-9.79, respectively. The trophically available cytoplasmic pool of Cu increased by 2 orders of magnitude in T. weissflogii cells (0.53 x 10(-17)-75 x 10(-17) mol Cu cell(-1)) grown with 10(-14.8)-10(-9.8) M free Cu. A 2-fold increase in intracellular and cytoplasmic Cu concentrations was observed in response to lowering the free concentration of the potentially antagonistic metal Zn by a factor of 10. However, the percent of intracellular Cu in the cytoplasmic fraction of T: weissflogii (congruent to 40%) was relatively constant over the range of cupric ion activities and [Cu(2+)]:[Zn(2+)] ratios applied. The assimilation efficiency (AE) of copper in marine copepods fed T. weissflogii, determined using the inert-tracer ratio method, was 40.3 +/- 6.3% for copepods fed diatoms grown at pCu = 12.79 and 50.3 +/- 9.7% for copepods fed diatoms grown at pCu = 10.79. Our results suggest that, above free Cu concentrations of 10(-11.8) M, the availability of Cu for trophic transfer in coastal waters increases as a result of rapidly increasing concentrations of Cu in the assimilable, cytoplasmic fraction of diatoms and potentially higher Cu AEs at the base of the pelagic food web.