Phytoremediation of arsenic-contaminated water by Lemna Valdiviana: An optimization study

Phytoremediation is a technique in which plants are used to treat contaminated media. The objective of this study was to monitor the influence of the parameters pH, phosphate concentration, and nitrate concentration in the process of arsenic absorption by Lemna valdiviana Phil. The response surface methodology was used to analyze the data to subsidize actions that maximize the phytoremediation process. A central composite rotational design (CCRD) was used with 3 variables including 6 axial points and 6 repetitions at the central point, totaling 20 trials. The plants were exposed to a constant concentration of arsenic in the optimization test of 0.5 mg L^-1 (NaAsO₂) and varied levels of pH, P-PO₄, and N-NO₃ in a period of 7 d. At the end of the experiment, the mass of arsenic removed from water and arsenic accumulated in the plants, the arsenic species present, the relative growth rate of plants (RGR), the tolerance index (TI), and the bioaccumulation factor (BAF) were calculated. Lemna valdiviana absorbed a greater amount of As when cultivated under pH conditions between 6.3 and 7.0, readily available phosphorus (P-PO₄) concentration of 0.0488 mmol L^-1, and nitrogen in the form of 7.9 mmol L^-1 nitrate. Under these conditions, the plants were able to accumulate 1190 mg kg^-1 As (in dry weight) from the aqueous media and reduce 82% of its initial concentration. Therefore, Lemna valdiviana has been shown to be an arsenic bioaccumulating macrophyte with high phytoremediation potential for media contaminated with the metalloid.