PH08 Metals in the Environment: Aquatic Biological Perspectives
Exhibit Hall
8:00 AM - Thursday
(PH074) Response of free and alginate-immobilized algal cells to heavy metal toxicity: A comparative study.
Abdel-Hamid, Mohammad I.1, 1 Botany Depatment, Faculty of Science, University of Mansoura, Egypt.
ABSTRACT- A simple toxicity testing procedure was adopted to study the effect of 12 heavy metals on growth of free and alginate-immobilized cells of the green chlorococcal alga Pseudokirchneriella subcapitata NIVA-CHL1. Freshly prepared and nine months old stock algae-alginate beads were included for comparison. The tested heavy metals were Al, As, Cd, Co, Cr, Cu, Hg, Se, Ni, Pb, Sr, and Zn. Biotests were carried out on polystyrene microplates containing 6 by 4 flat wells each of 3 ml capacity. Plates with free and immobilized cells were incubated for four days under conditions optimal for the growth of the test alga. Algal growth (dry weight) was used as toxicity response parameter. Toxicity values (EC50) were calculated by graphical interpolation from dose-response curves. Toxicity values rank the tested metals from the highest to the lowest toxic in the order Cd, Co, Hg, Cu, Ni, Zn, Cr, Al, Se, As, Pb, Sr. The lowest heavy metal concentration (mg l-1) inhibiting 50% (EC50) of algal growth of free and immobilized (values given in parentheses) algal cells were, 0.018 (0.09) for Cd, 0.03 (0.06) for Co, 0.039 (0.06) for Hg, 0.048 (0.050) for Cu, 0.055 (0.3) for Ni, 0.08 (0.1) for Zn, 0.2 (0.3) for Cr, 0.75 (1.8) for Al, 1.2 (1.4) for Se, 3.0 (4.0) for As, 3.3 (5.0) for Pb, and 160 (180) for Sr. Both free and immobilized cultures showed only similar responses to Cu and Se treatments. For the rest of metals tested, the free cells were more sensitive than the immobilized ones. The differences in corresponding EC50 values reported for free and immobilized cells were statistically significant (p≤0.05). EC50 values derived from biotests with fresh and stock algae-alginate beads were quite similar. A previous study (Abdel-Hamid, 1996) reported quite similar responses of free and immobilized cells of the test alga to a number of pesticides, and suggested that batteries of immobilized algae can replace free cultures in toxicity assessment of pesticides. This role is, seemingly, inapplicable for toxicity testing of heavy metals. The present study indicated that toxicity figures (EC50) of heavy metals derived only form immobilized algal cells might by questionable. However, the study may suggest that batteries of alginate-immobilized algae can efficiently replace free algae for the bioremoval of heavy metals.
Key words: Algal Bioassays, Heavy Metals, Pseduokirchneriella, Toxicity