Phytotoxicity and uptake of arsenic by ludwigia octovalvis in a pilot reed bed system

Arsenic (As) is in the first rank of dangerous and toxic chemicals. A phytotoxicity bioassay was used to select plant species for phytoremediation that were able to remove As from a contaminated site. Ludwigia octovalvis ( Jacq.) P.H. Raven has been described as a plant that can survive on a contaminated site in Malaysia. In this study, the phytotoxicity and uptake of As by L. octovalvis were examined at various As concentrations of 5, 22, and 39 mg/kg in a pilot reed bed system. The total extractable As and bioavailable As concentrations were determined using the wet digestion method and a solution of ethylene diamine tetraacetic acid disodium (Na2-EDTA) respectively. Results showed symptoms of phytotoxicity at all As concentrations after 42 days of exposure as the ratio of plant numbers to total mass of As was low. An increase in As-induced symptoms of phytotoxicity occurred with increasing As concentration in the spiked sand and with days of exposure. The concentration of the bioavailable As in the spiked sand decreased, and percentages removed were 76.5%, 72.0%, and 62.9% for initial As concentrations of 5, 22, and 39 mg/kg respectively. Maximum As uptake in stems reached approximately 1092.6 ± 106.7 mg/kg on day 14 at an As concentration of 39 mg/kg, while the maximum As uptake in roots and leaves on day 28 was 794.5 ± 110.4 and 883.9 ± 110.97 mg/kg respectively. An increase in As uptake by whole L. octovalvis plants occurred with increasing As concentration in the spiked sand, giving evidence that As can induce toxic effects on L. octovalvis when it is taken up and accumulated in its tissues.