The risk posed from incidental ingestion of arsenate-contaminated tailings may depend on sorption of arsenate to oxide surfaces in minerals. Popularly organic matter existing in tailings influenced bioaccessibility of arsenate. Arsenate adsorbed minerals were placed in simulated gastric and alveolar (in vitro) to ascertain the bioaccessibility of arsenate and changes in arsenate surface speciation caused by the biofluid systems. The effects of organic matter on arsenate bioaccessibility were investigated by adding oxalic and vanllic acid to biofluid systems. These results suggest that the bioaccessibility of arsenate is increased by organic matter and increasing reaction time.