Info

15 ± 2b

Values with the same letter in a column mean no significant differences

Values with the same letter in a column mean no significant differences

Fig. 24.3 Concentration of copper in water as function of time

Fig. 24.3 Concentration of copper in water as function of time

changes in the experimental treatments at this respect.

The final zinc concentration of the Lemna foliar tissue in the treatment with Zn was not significantly different from that of the control, but the copper concentration was significantly different. With respect to the initial concentration values of these essential elements, an increment was observed: from 24 to 330 mg kg-1 for Zn and from a value less than 4 to 15 mg kg-1 for Cu. Considering that the concentration in water was significantly higher than the concentration of Zn, the higher bioaccumulation capability of Zn of the plant Lemna minor is evident with respect to the Cu.

The concentration of copper in the water decreased within the time in the experimental treatment (Lemna + Cu + nutritive solution), evidencing that the element was absorbed by the plant and it was accumulated and used for the physiological functions (see Fig. 24.3).

The removal percentage from water was 31.24% after 18 days. The element was available in water during the entire experiment, as shown the Fig. 24.3. For the water without plants, initial concentration was 9.71 ± 0.27 mg L" 1 and final 9.25 ± 0.12 mg L-1. Although the nutritive solution contained Cu as essential element, the concentration in water of the control group was undetectable (less than 0.05 mg L-1) and the concentration in the plant tissue controls was below 4 mg kg-1 (quantification limit of the analytical method employed in this work). These results are in agreement with Zayed et al. (1998b) who demonstrated the high potential of the plant for the accumulation of Cu from waste waters. Nevertheless, Boniardi et al. (1999), on the contrary, expressed that concentrations higher than 1 mg L " 1 could be deleterious. Kabata-Pendias (2000) cited, regarding this fact, that a passive absorption in the toxic range could occur. The Cu mobility inside the plant tissue depended directly of the concentration in the substrate. This is observed in the experiment, since the plant progressively reduced the Cu concentration in the

Fig. 24.4 Concentration of zinc in water as function of time

Fig. 24.4 Concentration of zinc in water as function of time

(Zn+Nutritive solution+Lemna)

Zn+distilled water

Lemna+nutritive solution

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