In vitro evaluation of ferrihydrite as an enterosorbent for arsenic from contaminated drinking water

Arsenic (As) is a toxic trace element found in groundwater due to natural and industrial processes. Exposure has been linked to cancers of the bladder, lungs, skin, kidneys, nasal passages, liver, and the prostate. Arsenic in drinking water is a problem in many countries, notably Bangladesh and Taiwan. The purpose of this research was to utilize binding isotherms, a simulated gastrointestinal (GI) model, and the adult Hydra bioassay to evaluate ferrihydrite's potential to bind As and serve as a potential enterosorbent for As found in drinking water. A variety of clay minerals and synthesized iron oxides including ferrihydrite were screened for their ability to bind As(III), as sodium arsenite, and As(V), as sodium arsenate. After ferrihydrite was demonstrated to be the most effective sorbent for both As species, adsorption isotherms were performed. All isotherm data were fit to the Langmuir equation to determine adsorption capacity (Qmax). Ferrihydrite bound 96% of As(III) and 97% of As(V) in the screening studies and had a Qmax of 1.288 mol/kg for As(III) and 0.744 mol/kg for As(V). Using a simulated GI model, ferrihydrite was found to effectively adsorb As(V) and As(III) in the stomach and intestine. Ferrihydrite (0.25% w/w) protected adult Hydra at levels up to 200 times the minimal effective concentration (MEC) for As(III) and up to 2.5 times the MEC for As(V). These experiments confirm that ferrihydrite is a high capacity sorbent of As and that it is effective at removing As in a simulated GI model. These results suggest that ferrihydrite could be used as a potential enterosorbent for As found in drinking water. Future work will focus on verifying ferrihydrite's safety and efficacy in vivo.