ACCUMULATION OF CADMIUM, LEAD AND STRONTIUM, AND A ROLE OF CALCIUM-OXALATE IN WATER HYACINTH TOLERANCE

Eichhornia crassipes plants brought from the River Nile were cultured in jars containing river water supplemented with various concentration s of Cd, Pb, and Sr (0 to 100 mu g cm(-3)), added simultaneously. Trea tment continued for 20 d during which each cultivation solution was be ing replaced with fresh one every 3 d. The growth of Eichhornia was dr astically retarded at heavy metal concentrations higher than 15 mu g c m(-3). At concentrations 15 or 25 mu g cm(-3), the accumulation of Cd and Pb to levels several times higher than those in control plants was found. More than 50 % of the uptaken metals were retained by roots al one. Leaves and leaf petiols received around 30 and 20 % of the accumu lated metals, respectively. X-ray microanalysis indicated the presence of the three heavy metals in Ca oxalate crystals. Content of metals i n the crystals increased progressively over time of exposure in a way similar to those in whole plant tissues. These results suggest a possi ble role for Ca oxalate crystalization in toxic heavy metal deposition and thus tolerance by Eichhornia.