This field-scale hydroponic experiment investigated the effects of plant density and nutrient levels on arsenic (As) removal by the As-hyperaccumulator Pteris vittata L. (Chinese brake fern). All ferns were grown in plastic tanks containing 30 L of As-contaminated groundwater (130 microg x L(-1) As) collected from South Florida. The treatments consisted of four plant densities (zero, one, two, ...