Effect of pH, temperature, and oxygenation on arsenic phytofiltration by aquatic moss (Warnstorfia fluitans)

Phytofiltration of arsenic (As)-contaminated water could reduce As in irrigation and surface water. In a previous study, we found that the aquatic moss Warnstorfia fluitans efficiently removes arsenic from water contaminated with arsenate and arsenite. This work investigates how factors such as pH, temperature, and oxygenation influence As removal, since these factors vary in the environment. Plants were grown in a medium with 5 or 10 mu m arsenite or arsenate and: 1) a pH of 2.5, 6.5, or 9.5; 2) a temperature of 12, 20, or 30 degrees C; and 3) oxygenation of < 2 or 13 mg O-2 L-1. Removal of As was monitored over 48-96 h, and the content and speciation of As were analysed in moss plants at the termination of the experiments. Results indicate that As removal was faster in arsenite than arsenate solutions. Arsenic removal from arsenite solution was the fastest, i.e., 80-90% within 2 h, at pH 6.5 and 9.5 and at 20 and 30 degrees C. At pH 2.5, plants were stressed and the net removal was low throughout the treatment period. Arsenic removal was more efficient at low than high oxygenation levels. Besides this, no As net efflux process was seen in the water system except after 48 h in arsenate-treated medium in high-temperature (30 degrees C) regimes. Regardless of As species added, usually only arsenite was found in the plants after treatment. Most internal As, i.e., 95% in the arsenate and 85% in the arsenite treatments, was firmly bound to the tissue. The study found that at 20 degrees C, neutral pH, and low oxygenation, this aquatic moss has great potential for As phytofiltration.