Magnetite nanoparticles were synthesized with starch and sodium carboxymethyl cellulose (CMC) as a stabilizer, and tested for enhanced arsenate removal. Starch at >= 0.04 wt % or CMC at >= 0.005 wt % stabilized 0.1 g/L (as Fe) of the nanoparticles. While CMC-stabilized magnetite displays a highly negative zeta (zeta) potential, starch-stabilized magnetite shows a nearly neutral surface. Increasing the starch concentration from 0 to 0.04 wt % doubles the arsenate uptake, yet the nanoparticles remain settleable by gravity. Further increasing the starch concentration to 0.1 wt % results in fully dispersed nanoparticles and increases the arsenate uptake by 14%. Starch-stabilized magnetite offers a much faster sorption rate and greater capacity than CMC-stabilized magnetite. The sorption kinetics can be modeled using an intraparticle-diffusion model. The sorption capacity increases with decreasing pH. Dissolved organic matter at 20 mg/L as TOC decreases the arsenate uptake by 19.1%. When aged for >1.5 years, the nanoparticles did not show any arsenate leaching or particle dissolution.