This study reports on the uptake, potential bioavailability and phytotoxicity of arsenic (As) to an important wetland plant species growing in the vicinity of produced water discharge. The effects caused by As chemical form and concentration on growth, tissue concentrations and distribution of As and nutrient elements were studied inSpartina patens, growing in hydroponic conditions. A 4 × 3 factorial experiment was conducted with treatments consisting of four As chemical forms [arsenite, As(III); arsenate, As(V); monomethyl arsonic acid, MMAA; and dimethyl arsinic 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. DMAA was the most phytotoxic species to this marsh grass. As(V) and MMAA significantly increased total dry biomass production at low As rates of application. Arsenic availability followed the trend DMAA << MMAA ? As(V) < As(III). The As concentrations in root and shoot were significantly increased by increasing As application rates (all four species) to the rooting medium. Inorganic arsenicals and MMAA were mainly accumulated in roots, while DMAA was readily translocated to shoots. Arsenic chemical form and concentration significantly affected macro‐and micro‐nutrient concentrations in plant tissue. Plants treated with As(V) had an improved growth compared to control plants; this seemed to be associated to an increase in plant P concentrations. Organic arsenicals caused the highest Na root concentrations and simultaneously the lowest plant K levels (antagonism K‐Na). A significant decreased in leaf Ca concentrations was found in practically all As treatments. Organic arsenicals significantly decreased the concentrations of root Cu, Fe, and Mn and shoot B and Cu. The high phytotoxicity of the DMAA treatments appears to be related to the significant reductions in the concentrations of several essential macronutrients P, K, Ca, and Mg and micronutrients B, Cu, Fe, and Mn.