Diphenylarsinic acid(DPAA)is a phenyl arsenic compound derived from chemical warfare weapons.Macroscopic and microscopic work on DPAA sorption will provide useful information in predicting the partitioning and mobility of DPAA in the soil-water environment.Here,batch experiments and extended X-ray absorption fine structure(EXAFS)spectroscopy were used to investigate the sorption mechanisms of DPAA.The DPAA sorption data from 11 soil types was found to fit the Freundlich equation,and the sorption capacity,Kf,was significantly and positively correlated with oxalateextractable Fe2o3.The Kf values of eight of the 11 untreated soils(1.51113.04)significantly decreased upon removal of amorphous metal(hydr)oxides(0.51-13.37).When both amorphous and crystalline metal(hydr)oxides were removed from the untreated soils,the values either decreased or slightly increased(0.65-3.09).Subsequent removal of soil organic matter from these amorphous and crystalline metal(hydr)oxide-depleted samples led to ftirther decreases in A^f to 0.021.38,with only one exception(Sulfic Aquic-Orthic Halosols).These findings strongly suggest that ligand exchange reactions with amorphous metal(hydr)oxides contribute most to DPAA sorption on soils.EXAFS data provide further evidence that DPAA primarily formed bidentate binuclear(~C)and monodentate mononuclear(1 V)coring-sharing complexes with As-Fe distances of 3.34 and 3.66 A,respectively,on Fe(hydr)oxides.Comparison of these results with earlier studies suggests that 2C and 1 F complexes of DPAA may be favored under low and high surface coverages,respectively,with the formation of 1 V bonds possibly conserving the sorption sites or decreasing the steric hindrance derived from phenyl substituents.
Diphenylarsinic acid(DPAA)is both the prime starting material and major metabolite of chemical weapons(CWs).Because of its toxicity and the widespread distribution of abandoned CWs in burial site,DPAA sorption by natural Fe minerals is of considerable interest.Here we report the first study on DPAA sorption by natural magnetite and siderite using macroscopic sorption kinetics,sequential extraction procedure(SEP)and microscopic extended X-ray absorption fine-structure spectroscopy(EXAFS).Our results show that the sorption pseudo-equilibrated in 60 minutes and that close to 50%and 20%–30%removal can be achieved for magnetite and siderite,respectively,at the initial DPAA concentrations of 4–100 mg/L.DPAA sorption followed pseudo-secondary and intra-particle diffusion kinetics models,and the whole process was mainly governed by intra-particle diffusion and chemical bonding.SEP and EXAFS results revealed that DPAA mainly formed inner-sphere complexes on magnetite(>80%),while on siderite it simultaneously resulted in outer-sphere and inner-sphere complexes.EXAFS analysis further confirmed the formation of inner-sphere bidentate binuclear corner-sharing complexes(^(2)C)for DPAA.Comparison of these results with previous studies suggests that phenyl groups are likely to impact the sorption capacity and structure of DPAA by increasing steric hindrance or affecting the way the central arsenic(As)atom maintains charge balance.These results improve our knowledge of DPAA interactions with Fe minerals,which will help to develop remediation technology and predict the fate of DPAA in soil-water environments.
Meng ZhuYuhuan HeXiaobao WeiHaoran QiYunpeng ZhangYijun ZhangRuyi YangYongming Luo
