EFFECT OF CADMIUM AND LEAD ON NITRATE AND PHOSPHATE REMOVAL BY THE DUCKWEED LEMNA GIBBA

Abstract

In the present study, the effect of the heavy metals, such as cadmium and lead on the removal of nitrate (NO₃^-) and orthophosphate (PO₄^3-) was assessed using Lemna gibba. Duckweed plant was cultured in N and P-rich medium, supplemented with heavy metals. A total of two initials (0.1 and 1 mg/L) concentrations of Cd and Pb were used. Samples were taken every two days to assess plants efficiency in removing both nutrients and heavy metals over Six days.  Results showed that in control and in all treatments (Cd and Pb), nitrate and orthophosphate concentrations decreased markedly within the two days of initiating experiments as compared to the initial concentrations (1.76 ±0.01 mg P/L and 850±0.01 mg N/L).The highest phosphate removal efficiencies (percentage removal) were obtained on the fourth day at 1 mg Cd/L and 1 mg Pb/L. Whereas, nitrate removal showed maxima on the sixth day at 1 mg Cd/L and at 0.1 mg Pb/L. As compared to the control, the presence of Cd and Pb at 0.1 mg/L in the culture medium had no effect on phosphate removal, while a Pb concentration of 1 mg/L revealed a better phosphate removal. Cd and Pb at 0.1 mg/L enhanced nitrate removal as compared to control. Lemna gibba was able to simultaneously remove Cd, Pb, nitrate and phosphate, major causes of contamination and eutrophication in water bodies.