The Effect Of Metal Ions On The Interaction Between Dissolved Organic Matter And Arsenic Compounds

In recent years, several arsenic pollution incident occurred frequently around world, which has brought a great harm to environment. In order to solve the arsenic pollution, the migration and transformation of arsenic in environment as well as the pollution controll have been research focuses nowadays. There are lots of research shows that both the dissolved organic matter(DOM) and metal ions have a great effecy on migration and transformation of arsenic. However, the synergistic effect of DOM and metal ions on migration and transformation of arsenic still need further research. In this paper, four typical metal ions (Fe3+?Cu2+?Mg2+?Zn2+),three different species of arsenic [including: inorganic arsenic (arsenious acid, As(?); arsenic acid,As(V) ), organic arsenic (roxarsone, ROX; p-arsenic acid , p-ASA), methylarsonic acid(monomethylarsonic acid, MMAA; dimethylarsenic acid, DMAA)] and humic acid (HA, as a represent of DOM) were chosen as represents of metal ions, arsenic,and dissolved organic matter, respectively. The target of this research is to investigate the influence of metal ions on the interaction between DOM and arsenic, and the influence of metal ions on arsenical bio-availability. The fluorescence quenching,atomic force microscope, high performance liquid chromatography and ICP-MS were used in this research. The results can serve as theoretical and practical basis of controlling arsenic pollution. The specific results are listed below:(1) Fe3+?Cu2+, Zn2+, Mg2+ can interact with the function group of HA, and change the fluorescence intensity of HA-arsenic. The results shows that metal ions can influence the interaction between HA and arsenic in different degree. Fe3+, Cue2+,Zn2+ can decrease the fluorescence intensity of HA-As(III), HA-As(V), HA-ROX,HA-p-ASA and HA-MMAA, and increase the fluorescence intensity of HA-DMAA.While Mg2+ can increase the fluorescence intensity of HA-As(III), HA-As(V),HA-ROX and HA-DMAA. Fe3+, Cue+, Zn2+ can change the properties of HA function group, so that influence the interation between HA and arsenic. The way how metal ions influence the interaction is various: including redox reaction, complexation and forming cation ions. However, Mg2+ can form a hydration layer on the surface of HA,and compete with arsenic, thus, it will influence the interaction between HA and arsenic.(2) Fe3+, Cu2+, Zn2+ and Mg2+ can change the double-electric layer of HA, and change the Zeta potential of HA-arsenic colloid, meantime, they also can cause the aggregation of HA-arsenic molecule. The results show that: Fe3+, Cu2+, Zn2+ and Mg2+can decrease the absolute value of Zeta potential in HA-As(?), HA-As(?), HA-ROX,and HA-p-ASA, decrease the stability of system, and cause the aggregation of molecule. For methylarsonic acid system, Fe3+can decrease the absolute value of Zeta potential in HA-MMAA, decrease the stability of HA-MMAA system, cause the aggregation of HA-MMAA molecule. Meantime, Cu2+, Zn2+ and Mg2+ can increase the absolute value of Zeta potential in HA-MMAA. What's more, Fe3+, Cu2+ and Mg2+can decrease the absolute value of Zeta potential in HA-DMAA, and decrease the stability of system, and cause the aggregation of HA-DMAA molecule. While Zn2+will increase the absolute value of Zeta potential in HA-DMAA, and increase the stability of system.(3) Fe3+, Cu2+, Zn2+ and Mg2+ change the concentration of free and bound arsenic,as well as the value of logKD in HA-arsenic system, so that influence the binding action between HA and arsenic.The results show that: For HA-inorganic arsenic system, low concentration of Fe3+, Zn2+ can impede the binding action between HA and As(?), and low concentration of Zn2+ can impede the interaction between HA and As(?). However,Cu2+,high concentration of Fe3+and Zn2+can promote the interaction between HA and As(?), As(?).For HA- phenylarsonic acid system, low concentration of Fe3+ and Cu2+ will impede the interaction between HA and ROX while Zn2+, high concentration of Fe3'and Cu2+ will promote the interaction between HA and ROX. Mg2+ can impede the binding action of HA and ROX. Meantime, all of Fe3+,Cu2+, Zn2+ and Mg2+ can promote the interaction between HA and p-ASA.For methylarsonic acid system, low Fe3+ and Cu2+ can impede the interaction between HA and MMAA while high concentration of Fe3+ and Cu2+ can promote the interaction between HA and HA-MMAA. However, Mg2+ will impede the binding action of HA and MMAA, and the influence of Zn2+ on interaction between HA and MMAA varing with the concentration change. Fe3+, Cu2+, high concentration Zn2+ and Mg2+ can promote the interaction between HA and DMAA.Low concentration of Fe3+,Cu2+ and Zn2+ will compress the double-electron layer of HA, and cause the aggregation of HA, decrease its binding sites, thus, impede the interaction between HA and some arsenic. High concentration of Fe3+,Cu2+ and Zn2+ can form cation bridges to promote the interaction of HA and some arsenic.Zn2+ will compete with As(V) on binding sites of HA. What's more,Mg2+ will a hydration layer on the surface of HA, shield binding sites of HA, so that impede the interaction between HA and some arsenic.(4) In general, Fe3+, Cue+, Zn2+, Mg2+ can cause the change on fluorescence intensity, aggregation of HA molecule and Zeta potential of HA-As system. Meantime,it can influence the interaction between HA and arsenic, promote/impede the binding action between them, and affect the release of free arsenic.