Distribution of Radioactive and Stable Zinc in an Experimental Marine Ecosystem

Abstract

The distribution of radioactive and stable Zn in an experimental marine ecosystem is described. We added 1 mCi of 65Zn to 2000 liters of sea water and a mixed community of planktonic and benthic algae in a fiberglass tank, after which the ecosystem was left undisturbed for 9 months. We then measured the 65Zn specific activities for (1) particulate Zn (0.45 μ filterable), (2) extractable Zn (from water passed through a 0.45-μ filter and then treated with dithizone), (3) total dissolved Zn (from samples passed through a 0.45-μ filter and treated with acid prior to extraction with dithizone), and (4) dialyzable Zn. Zinc-65 specific activities were not significantly different among the extractable, dialyzable, or acid-treated samples of the water. Further, absolute concentrations of 65Zn and total Zn were no higher in the acid-treated samples than in the extracted or dialyzed samples, which indicates that nearly all of the soluble Zn in the water was dithizone-extractable and dialyzable. Zinc-65 specific activities were significantly less, however, in the particulate material than in the water. This difference indicates that equilibrium of Zn between particulate material and water had not been reached after 9 months. Three months later (December 1969) 65Zn specific activities were determined again for particulate material and total dissolved Zn. The mean specific activity of 65Zn in the particulate samples showed a small but significant increase, but it was still less than in the water. Concentration factors in the particulate matter were 980 for 65Zn and 1400 for total Zn. Samples of benthic algae taken in March 1970 had a mean specific activity of 65Zn similar to the mean 65Zn specific activity of water samples taken 3 months earlier.