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 and toxicity of Cr by Lemna minor L. The plants were grown in full-strength 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 sets without EDTA, growth of L minor was inhibited as the concentration of Cr in medium increased. In treatments with 10.0 ppm Cr, relative growth 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 ion concentration in L minor fronds increased with increasing Cr concentration in growth medium. Statistical data analysis revealed that both growth and bioaccumulation were dependent on the concentration of Cr and the effect of pH was insignificant at levels 5.0, 6.0 and 7.0. In studies with EDTA, growth of L minor was affected by Cr concentration in medium and pH. In test sets supplemented with EDTA between 40 and 200 mu M concentrations, growth inhibition was observed at all Cr concentrations at pH 5.0 and 6.0 but only above 2 ppm for pH 7.0. The highest 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 as 14% at 10 ppm Cr with 40 mu M of EDTA and at pH 5.0. Further,statistical data analysis indicated that the concentration of metal ion and pH influenced the bioaccumulation. However, the former parameter was more significant than the latter on the variable accumulation. (C) 1998 Elsevier Science Ltd. All rights reserved.