Phytoremediation of arsenite-contaminated environments: is Pistia stratiotes L. a useful tool?

摘要

Phytoremediation is considered an ecologically beneficial technique for removing arsenic from aquatic environments but studies on the mechanisms of tolerance to this pollutant, when present in the form of arsenite (As-III) still need to be performed. Thus, in order to evaluate the potential of Pistia stratiotes to phytoremediation of As-III and the morphological and biochemical responses involved in metalloid tolerance, P. stratiotes plants were exposed to four treatments: 0 (control), 5, 10 and 20 mu M As-III, remaining under treatment for 24 h for biochemical analysis and for 4 days to analyze the arsenic (As) uptake, biomass production, bioconcentration factor (BCF), translocation factor (TF) and visual symptomatology. The plants were able to accumulate As in both roots and leaves. This accumulation was higher in the treatment with 10 mu M As-III (1120.40 and 31.60 mu g g(-1) dry weight in roots and leaves, respectively), decreasing in the following concentration. P. stratiotes also showed a high BCF, that was higher than 1000 when exposed to 5 and 10 mu M As-III (1808.38 and 1536.02, respectively). The pollutant was maintained mainly at the root (TF was always lower than 1.0) which may be a defense mechanism of aquatic plants to As. Despite the significant accumulation of pollutant, the plants were able to maintain growth in all evaluated concentrations, although in very different proportions. In fact, while in the lower concentration of As the biomass production was not affected, in the treatment with 20 mu M As-III the dry biomass decreased in approximately 77%. The accumulation of As resulted in the appearance of visual symptoms of toxicity such as chlorosis, darkening and reduction of the root system, which were more conspicuous in the highest As concentration. The metalloid exposition also triggered biochemical alterations, increasing the membrane damage and the reactive oxygen species (ROS) levels and, once again, these damages were more intense in the plants exposed to 20 mu M As-III. The action of the antioxidant system (especially in the leaves) and the compartmentalization of the pollutant in the root system apparently was important in the P. stratiotes response to toxic compounds and allowed the plants to maintain the cell homeostasis and the growth at the two lowest As concentrations. Thus, the data suggest that P. stratiotes may has a potential for phytoremediation of aquatic environments contaminated with As-III concentrations close to 10 mu M.