EFFECTS OF PH AND CHELATOR EDTA ON CR TOXICITY AND ACCUMULATION IN LEMNA-MINOR

A factorial culture experiment was designed to investigate the effects of pH and EDTA (Ethylenediaminetetraacetic acid) on bioaccumulation a nd toxicity of Cr by Lemna minor L. The plants were grown in full-stre ngth Jacob Culture Medium of varying Cr concentrations from 1.00 mu M to 10.0 mu M supplemented with or without EDTA. Each experiment was Nn at pH levels 5.0, 6.0 and 7.0 for a 7-day exposure period. In test se ts without EDTA, growth of L minor was inhibited as the concentration of Cr in medium increased. In treatments with 10.0 ppm Cr, relative gr owth rate values as percentage of control sets reached to a low of 23% , 32%, and 54% at pH levels 5.0 6.0 and 7.0 respectively. The metal io n concentration in L minor fronds increased with increasing Cr concent ration in growth medium. Statistical data analysis revealed that both growth and bioaccumulation were dependent on the concentration of Cr a nd the effect of pH was insignificant at levels 5.0, 6.0 and 7.0. In s tudies with EDTA, growth of L minor was affected by Cr concentration i n medium and pH. In test sets supplemented with EDTA between 40 and 20 0 mu M concentrations, growth inhibition was observed at all Cr concen trations at pH 5.0 and 6.0 but only above 2 ppm for pH 7.0. The highes t relative growth rate as percentage of controls was 131% at 1 ppm Cr with 200 mu M of EDTA and at pH 7.0 and the lowest data was recorded a s 14% at 10 ppm Cr with 40 mu M of EDTA and at pH 5.0. Further,statist ical data analysis indicated that the concentration of metal ion and p H influenced the bioaccumulation. However, the former parameter was mo re significant than the latter on the variable accumulation. (C) 1998 Elsevier Science Ltd. All rights reserved.