The fresh and dry biomass were significantly reduced due to the climatic conditions of the experiment, which also negatively influenced the growth rate (Alvarado et al. 2008). This effect was more pronounced in the dry biomass of the control (without As). In wet basis (fresh biomass), nonsignificant differences were found between treatments as consequence of the higher humidity percentage in plants of the control and also due to a more slow generational change in the presence of the arsenic in the experimental treatment. This fact is confirmed with the percentage of dry matter at the end of the experiment. There are significant differences between treatments and a higher percentage of dry matter was observed in the experimental treatment at the end of the experiment, when compared to the control (see Table 24.3).
The lower concentration of the element in water corresponded to the 14th day of the experiment and it is in agreement with the maximum concentration in tissue. After the 14th day, there was a release of the element to water as a consequence of tissue death (Alvarado et al. 2008).
The mass of arsenic removed and the removal rate for Lemna minor were low with respect to the initial arsenic level, but the bioaccumulation factor was 16. The harvest of plants must be performed in longer periods for the efficient removal of the contaminant or higher plant densities must be used.
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