. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 124 Al. SCHULZ-BALDES AND R. A. LEWIN 0020- PHAEODACTYLUM 3 days. 0 30 60 90 minutes 120 FIGURE 6. Phaeodactylum tricornutum : lead content of cells, previously exposed to mg Pb/1 for 5 min or 3 days, and then treated with 10~2 M EDTA, as a function of time. The capacity of Phaeodactylum cell surfaces to adsorb lead was determined by supending cells for ten minutes in media containing a rather high concentration of dissolved lead, removing them by centrifugation, and determining the amounts of lead taken up. Despite dif
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 124 Al. SCHULZ-BALDES AND R. A. LEWIN 0020- PHAEODACTYLUM 3 days. 0 30 60 90 minutes 120 FIGURE 6. Phaeodactylum tricornutum : lead content of cells, previously exposed to mg Pb/1 for 5 min or 3 days, and then treated with 10~2 M EDTA, as a function of time. The capacity of Phaeodactylum cell surfaces to adsorb lead was determined by supending cells for ten minutes in media containing a rather high concentration of dissolved lead, removing them by centrifugation, and determining the amounts of lead taken up. Despite differences in cell numbers and lead concentrations, we found that the same amount of lead was adsorbed per cell (Table III), suggesting a limited number of binding- sites. These were all occupied by a lead load of 11,640 /ig/g dry weight, equivalent to X lO^13 g or X 10s Pb-atoms per cell. Considering the surface of a Phacodactylnin cell as a frustum of a right double cone 20 /mi long and 6 to 3 /xm wide, with an area of 440 /xiir, we calculate that about atoms of lead can be absorbed per nnr. Only uncomplexed lead is available for adsorption, as demonstrated in an experi- ment with different concentrations of EDTA added immediately before the lead treatment. About 2 X 10"° M EDTA completely inhibits lead uptake from a X 10'6 M solution ( mg Pb/1) (Fig. 5). Probably other ions are chelated, too, but even at lower EDTA concentrations some of the lead is eluted from the algae after its initial adsorption. In order to test how tightly the lead is bound on the algae, "leaded" cells were treated with 10 2 M EDTA. This high concentration (which kills the algae within 24 hours) within 20 minutes reduces the lead content the cells to a certain level which is evidently dependent on the previous time of ead exposure (Fig. 6). The hound lead content of Phitynwnas and Phaeodactylum, ., that fraction which remains associated with the cells after a one-hour t
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