Uptake of Heavy Metals by Water Hyacinth, Eichhornia crassipes (Mart)

Abstract

Water hyacinth, Eichhornia crassipes was used to conduct a 15-day study on the uptake of heavy metals Lead (Pb); Cadmium (Cd) and Copper (Cu). 5 plants were in each case emersed in each of graded metal salt solutions (5, 10 and 15mg/l) over a 15 – day period. Metals in plant and water samples were analyzed to determine their metal concentrations by means of an atomic absorption spectrometer (AAS) in separate experiments. Results show that by day 3 of the study period, more than 90% of the metal ions in solution were taken up by the plant. In the 5mg/l treatment, metal uptake increased from day 3 to day 12 as follows: Pb, from 0.263 to 0.344mg/kg; Cd, 0.315 to 0.357mg/kg and Cu, 0.191 to 0.287mg/kg while metal ions decreased in the original solution as follows: Pb, from 0.017 to 0.009mg/l; Cd, 0.169 to 0.122mg/l and Cu, 0.430 to 0.190mg/l. In the 10mg/l treatment, increase in metal ions uptake from day 3 to day 12 were as follows: Pb, from 0.201 to 0.282µm/kg Cd, 0.275 to 0.478 mg/kg and Cu, 0.337 to 0.384 mg/kg. Metal ions decrease in the original solution were as follows: Pb, from 0.021 to 0.012mg/l; Cd, 0.404 to 0.302mg/l and Cu, 0.598 to 0.328mg/l. In the 15mg/l treatment, metals uptake increase were: Pb from 0.237 to 0.283mg/kg; Cd, 0.330 to 0.488mg/kg and Cu, 0.359 to 0.538mg/kg while metal values decrease in the original solution were: Pb, 0.008mg/l, Cd, 0.416mg/l and Cu, 0.348mg/l from day 3 to day 9. Plants in the 15mg/l treatment did not survive beyond day 9 of the study period. Significant differences (F = 2.3479, P <0.05) were recorded in the concentrations of metals taken up by plants in the 5-plant scheme. Pb had the highest mean bioaccumulation quotient and had the highest uptake. The concentrations of metals left in solution were below the limits recommended by the Federal Ministry of Environment (FMENV) and the World Health Organization (WHO) for portable drinking water.