Takao Horikoshi

Studies on the accumulation of heavy metal elements in biological systems

SummaryThe selective accumulation of heavy metal ions byChlorella regularis was investigated. The amounts of heavy metal ions taken up byChlorella cells decreases in the following order:

Accumulation of cadmium by green microalgae

\begin{gathered} UO_2^{2 + } \gg Cu^{2 + } \gg Zn^{2 + } \gtrsim Ba^{2 + } \bar \sim Mn^{2 + } \gtrsim Co^{2 + } \bar \sim Cd^{2 + } \hfill \\ \gtrsim Ni^{2 + } \bar \sim Sr^{2 + } \hfill \\ \end{gathered}

Adsorption of Uranium by Chitin Phosphate and Chitosan Phosphate

for livingChlorella cells and:

Uptake of Uranium by Chlorella regularis

\begin{gathered} UO_2^{2 + } \gg Cu^{2 + } \gg Mn^{2 + } \gtrsim Ba^{2 + } > Zn^{2 + } \gtrsim Co^{2 + } \gtrsim Cd^{2 + } \hfill \\ \gtrsim Ni^{2 + } > Sr^{2 + } \hfill \\ \end{gathered}

Uptake of Uranium from Sea Water by Microalgae : Studies on the Accumulation of Heavy Metal Elements in Biological Systems (VI)

for heat-killedChlorella cells.To determine which components ofChlorella cells are involved in heavy metal ion binding, the uptake of heavy metal ions by chemically treatedChlorella cells and byChlorella cell walls was studied. The cell components which remain after alkali extraction play a fairly important role in heavy metal ion binding while those which remain after extraction with hot water or chloroform-methanol and the cell fraction obtained with a chloroform-methanol/concentrated alkali treatment are involved, but to a lesser extent, with heavy metal ion binding. It is suggested that uptake of heavy metal ions byChlorella cells is dependent on adsorption by proteins and that the amount of adsorption varies for each heavy metal ion. Uranyl ion was most readily taken up by the cells and the uptake of cadmium ion by the cells was low because of the presence of and competition from uranyl and copper ions.To investigate which component of heat-killedChlorella cells is involved in heavy metal ion binding, the uptake of heavy metal ions by heat-killedChlorella cells treated with acid was studied. The acid extracted components were mainly responsible for copper and cadmium ion binding but only slightly responsible for the binding of uranyl ion.

Ion Effects on the Uptake of Uranium by Chlorella regularis

SummarySome attempts were made to recover uranium from sea and fresh water using immobilized Streptomyces viridochromogenes and Chlorella regularis cells. The cells immobilized in polyacrylamide gel have the most favorable features for uranium recovery; high adsorption ability, good mechanical properties, and applicability in a column system. The adsorption of uranium by the immobilized cells is not affected by the pH values between 4 and 9. These results show that uranium adsorption becomes independent of pH after immobilization. The amounts of uranium adsorbed by the immobilized cells increased linearly with temperature, suggesting that the adsorption of uranium by the immobilized cells is an endothermic reaction. The immobilized cells can recover uranium almost quantitatively from both fresh and sea water containing uranium, and almost all uranium adsorbed is desorbed with a solution of Na2CO3. Thus the immobilized cells of Streptomyces and Chlorella can be used repeatedly in adsorption-desorption process.