The arsenic masses in the tissue and water for the Lesser Duckweed
and Water Hyacinth are shown in Figs. 1 and 2. The minimal
amount of the element in water for both species is found at the
14th day of the experiment and it is in agreement with the maximum
concentration in tissue for both species. After the 14th day
there was a release of the element to water, as consequence of tissue
death in both species. A higher accumulation in the tissue of
the Water Hyacinth was observed (see Figs. 1 and 2).
The mass of arsenic removed and the removal rate for the Lesser
Duckweed were low with respect to the initial arsenic level. This
means that the plants should be collected during a longer period
in order to remove the contaminant, to achieve a long residence
time and the management of higher biomasses and residues. The
arsenic absorbed mass and removal rate of the Water Hyacinth
suggest that this plant has a better capability for the removal of
the element during the first 14 days. The species must be harvested
every 15th days in order to avoid the release of the arsenic to the
water.