Studies on the accumulation of heavy metal elements in biological systems

Summary

The 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:

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

for livingChlorella cells and:

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

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.