Co-adsorption Of Sodium Arsenate And Serine At Mineral/Water Interface

BackgroundThe inorganic arsenic(iAs)is the class one carcinogen suggested by the International Agency for Research on Cancer(IARC).As one of the most significant threats to human health,the arsenic poisoning can cause cancer,congenital maiformation,and diseases of the nervous system,cardiovascular system,etc.The iAs gets into the atmospheres,waters,soils,and sediments by means of mineral weathering and emissions from industrial and agricultural production.The iAs intakes for people,livestock,and poultry come from the direct contact and food chain.Notably,the iAs can easily adsorb on the minerals of soils and sediments,and the adsorption mechanisms are considered as the important factor for its distribution between the soils and soil solutions as well as the sediments and pore waters.Consequently,the adsorption processes at mineral/water interface refer to the migration rate and bioavailability of iAs,affecting its potential risks to ecology and human health.ObjectiveBased on the adsorption mechanisms of As(Ⅴ)and serine on TiO2,this study aims to reveal the transport and transformation of iAs in the environment,and to predict its risks to ecology and human health.MethodThe combined attenuated total reflectance Fourier transform infrared(ATR-FTIR)spectroscopy and DFT calculations were used to reveal the surface complexation and adsorption characteristics for arsenate and serine adsorption on TiO2.The coadsroption study was based on the conclusions of TiO2-As(Ⅴ)and TiO2-serine systems.The pH and reaction time were both selected as the influencing factors.In natural environments,the adsorption on minerals is rather complicated because of the abundant coexisting constituents.The typical neutral amino acid serine is an important part of the dissolved organic nitrogen(DON)and small organic acids.TiO2 is one of the most frequently studied minerals with wide applications.The iAs can adsorb on the accumulated TiO2 in the environment,which affects its release processes and chemical forms in soils and sediments.ResultAs for single As(Ⅴ)adsorption TiO2,H2AsO4-(pH 4)and HAsO42-(pH 8)attached to the TiO2 surface sites in the form of mononuclear monodentate type inner-sphere complexation.As for serine adsorption alone,two binuclear bidentate complexes were resolved at pH 4～8(typeⅠ)and pH 10(type Ⅱ)involving the COO-group.In the coadsorption processes,As(Ⅴ)and serine competed for the available surface sits at the TiO2/water interface.Interestingly,the competition did not change the inner-sphere surface complexation of As(Ⅴ)on TiO2,but resulted in the structure changes of adsorbed serine zwitterion from bidentate coordination to monodentate coordination.ConclusionThe inner surface complexation of TiO2-As(Ⅴ)can accelerate the migration of As(Ⅴ)from water environment to soil,sediment and other environmental media,and fix on the mineral/water interface relatively stably.In addition to the release of nutrient nitrogen,the competitive adsorption facilitates the As(Ⅴ)migration from the mineral surfaces to the soil and sediment water environments,increasing its potential risks to ecology and human health.These results provide new and complementary information for As(Ⅴ)and serine adsorption on minerals,promoting further research on the co-adsorption of iAs with metal ions,oxyanions,small organic acids,and humic acids at the molecular level.