Chemical and Physiological Investigations on Heavy Metal - Phytoplankton Interactions

Abstract

<p>Binding of zinc-65 to the surface of Chlamydomonas was reduced by 60-80% under suboptimal physiological conditions of light, temperature, and pH. Zinc bound to the surface was composed of a labile fraction and a non-exchangeable fraction. The non-exchangeable fraction corresponded to the quantity bound under suboptimal conditions. Maximum surface binding capacities for zinc in 7 species of phytoplankton were compared and support metal ion exclusion as a potential tolerance mechanism. Factorial experiments were conducted to assess the effects of Cu, Sr, Ni, Cd, Mn, Ca, Mg, and Co (singly and in all combinations) on zinc uptake, fluorescence, and photosynthesis in 5 species of phytoplankton. The results provide valuable insights into the nature of interaction between metals and the observed response (antagonistic, synergistic, or independent).</p> <p>The effects of metals on the growth of Chlamydomonas were as follows; Hg>Cu>Cd>Ni=Zn>Co>Cr>Fe=Be=Sr. Growth of laboratory strains and field isolates exposed to metals could be classified either by an extended lag phase or a gradual reduction in cell numbers over time. The nature of the response was related to changes in the available metal concentration over time, kinetics of binding and uptake, and the mode of toxic action (surface or internal sites).</p> <p>Field studies were conducted on the fates of Ni, Cd, Cu, Pb, Zn, Co, and Sr added to closed, 8000 L limnocorals located in Hamilton Harbour, Hamilton, Ontario. Sedimentation was the principal mechanism regulating the availability of heavy metals in situ with rates dependent upon; 1. the reactivity of individual metals (affinity for particulates), 2. biological factors (contributions to particulate phase) and 3. physical stability and chemical composition of the water column.</p> <p>Important kinetic interactions between variables and processes regulating the binding of metal to the cell surface, uptake, and the observed toxic response were incorporated into a dynamic model to simulate the effects of metal stress on phytoplankton growth and metal uptake.</p>