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Presented here is the influence of membrane pore size and dissolved organic matters on the diffusion coefficient (D) of aqueous arsenate,investigated by the diffusion cell method for the first time.The pH-dependent diffusion coefficient of arsenate was determined and compared with values from previous studies;the coefficient was found to decrease with increasing pH,showing the validity of our novel diffusion cell method.The D value increased dramatically as a function of membrane pore size at small pore sizes,and then increased slowly at pore sizes larger than 2.0 μm.Using the ExpAssoc model,the maximum D value was determined to be 11.2565 × 10-6 cm2/sec.The presence of dissolved organic matters led to a dramatic increase of the D of arsenate,which could be attributed to electrostatic effects and ionic effects of salts.These results improve the understanding of the diffusion behavior of arsenate,especially the important role of various environmental parameters in the study and prediction of the migration of arsenate in aquatic water systems.