Arsenic in wetland vegetation: Availability, phytotoxicity, uptake and effects on plant growth and nutrition

In wetland surface sediments of Louisiana, arsenic (As) concentrations are elevated because of a wide use of inorganic arsenicals as cotton desiccants and of organic arsenicals as herbicides in rice-producing areas. Beside this, As levels are even higher in the region of produced water discharge associated with petroleum hydrocarbon recovery operations. The uptake, potential bioavailability and phytotoxicity of As to an important wetland plant species, growing in the vicinity of produced water discharge sites, were studied. The effects caused by As chemical form and concentration on growth, tissue concentrations and distribution of As and nutrient elements were studied in Spartina alterniflora growing in hydroponic conditions. A 4×4 factorial experiment was conducted with treatments consisting of four As chemical forms [arsenite, As(III); arsenate, As(V); monomethyl arsonic acid, MMAA; and dimethylarsinic acid, DMAA] and four As concentrations (0, 0.2, 0.8 and 2.0 mg As l−1). Arsenic phytoavailability and phytotoxicity were primarily determined by the As chemical form present in the nutrient solution. MMAA was the most phytotoxic species to this marsh grass. Regardless of the chemical form, an As level in the nutrient solution of 0.2 mg l−1 was safe or caused no toxic effects for this marsh grass (it did not reduce plant growth or interfere with plant nutrition). In fact, inorganic arsenicals significantly increased total dry biomass production at an application rate of 0.2 mg l−1. Arsenic availability followed the trend DMAA≪MMAA