IWRA Proceedings

AbstractTHE USE OF THE AQUATIC PLANT LEMNA GIBBA IN WATER –TOXICITY CONTROL: INVESTIGATION OF CADMIUM EFFECTS THROUGH CHEMICAL MODIFICATIONS IN AQUATIC SYSTEM WITH PLANT S. SEMSARI, F. TALEB, S. MEGATELI and K.TAHAR University of Blida, Department of Industrial Chemistry, Route de Soumaa, POB 270, 09000 Blida, Algeria Key words: Contaminants, Heavy metals, Bio monitoring, Aquatic Plants. Abstract: Among species laboratory tests, aquatic plants have been used as tool for monitoring particularly metal contamination in aquatic ecosystem. The objective of this laboratory study was to examine the response of an aquatic plant, Lemna gibba, through chemical changes involving nitrogen, calcium and magnesium metabolism in the culture medium to simulated cadmium discharges. The principal purpose of this study was to present the composition of nitrogen, alkalinity, calcium and magnesium in uncontaminated and contaminated growth medium of Lemna gibba and to present results that demonstrate the relationship of nitrogen medium content and the inhibition of growth to the concentrations of cadmium adsorbed by Lema gibba. Plant was cultured under sterilized conditions in a medium inspired of that proposed by Hoagland. The experiments were illuminated 16 h per day at 24 ± 2°C in thermostatically controlled growth chamber. For all experiments the plants of the third generation were used and each test was started with 04 colonies into 100 ml of experimental solutions. Plants were washed prior the incubations using diluted sodium hypochlorite solution to remove the possibility of the micro algae development. In each experiment, growth of new fronds of Lemna gibba were examined and ammonia-nitrogen, nitrite, nitrate, alkalinity, calcium and magnesium in the growth media were assayed according experiment durations: 2, 4, 6, 8 and 10 days. In the experiment involving cadmium, the plants were exposed to concentrations of cadmium: 10-3; 10-2 and 10-1 mg.L-1 for experiment duration of 10 days. All experiments were carried out in 04 replicates and the data presented are the average of four replicates ± standard error of means. The results of this study indicated that a great level of product ammonia in Lemna gibba growth medium come from nitrate reduction and from a symbiotic micro organisms excretion when plants was not treated by sodium hypochlorite before its culture. The results obtained under sterilization-treatment of plant showed that the absorption of nitrate-nitrogen by the plants appears to be significantly disturbed by the presence of cadmium. The reduction rate of the nitrate uptake process decreased significantly (p = 0.012 < 0.5) whith increasing cadmium from (10-3 to 10-1) mg.L-1) and respectively within period of time t, from: (26.01; 37.28) to (6.58; 9.77) (t = 4 days), (30.36; 56.19) to (10.54; 19.58) (t = 6 days) and (41.63; 99.99) to (17.91; 43.92) (t = 10 days). It’s therefore suggested that the decreasing of nitrate concentrations in the growth medium could constitute a tool for detecting water metal contamination. From the results one showed an increase in the pH values and alkalinity, with increasing time, depending in metabolization results. Calcium and magnesium composition of contaminated solutions were also significantly modified.