Adsorption of As(III), As(V) and dimethylarsinic acid onto synthesized lepidocrocite

Simultaneous Speciation Analysis of Arsenic, Chromium, and Selenium in the Bioaccessible Fraction for Realistic Risk Assessment of Food Safety

A simple and fast method was developed for risk assessment of As, Cr, and Se in food, which is demonstrated here using three cooked and uncooked rice samples (basmati as well as organic white and brown rice). The bioaccessible fraction was first determined through online leaching of rice minicolumns (maintained at 37 °C) sequentially with artificial saliva, gastric juice, and intestinal juice while continuously monitoring potentially toxic elements (As, Cr, and Se) by inductively coupled plasma mass spectrometry (ICPMS). Then, a new ion chromatography method with online detection by ICPMS was developed for the simultaneous speciation analysis of As, Cr, and Se in the bioaccessible fraction to determine the portion of these elements that was actually toxic. Using gradient elution, four As species [As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid], two Cr species [Cr(III) and Cr(VI)], and two Se species [Se(IV) and Se(VI)] were separated within 12 min. The simultaneous speciation analysis of As, Cr, and Se revealed that the simple act of cooking can convert all of the carcinogenic Cr(VI) to the safer Cr(III).

Stimulation of Fe(II) Oxidation, Biogenic Lepidocrocite Formation, and Arsenic Immobilization by Pseudogulbenkiania Sp. Strain 2002

An anaerobic nitrate-reducing Fe(II)-oxidizing bacterium, Pseudogulbenkiania sp. strain 2002, was used to investigate As immobilization by biogenic Fe oxyhydroxides under different initial molar ratios of Fe/As in solutions. Results showed that Fe(II) was effectively oxidized, mainly forming lepidocrocite, which immobilized more As(III) than As(V) without changing the redox state of As. When the initial Fe/As ratios were kept constant, higher initial Fe(II) concentrations immobilized more As with higher Asimmobilized/Feprecipitated in biogenic lepidocrocite. EXAFS analysis showed that variations of initial Fe(II) concentrations did not change the As-Fe complexes (bidentate binuclear complexes ((2)C)) with a fixed As(III) or As(V) initial concentration of 13.3 μM. On the other hand, variations in initial As concentrations but fixed Fe(II) initial concentration induced the co-occurrence of bidentate binuclear and bidentate mononuclear complexes ((2)E) and bidentate binuclear and monodentate mononuclear complexes ((1)V) for As(III) and As(V)-treated series, respectively. The coexistence of (2)C and (2)E complexes (or (2)C and (1)V complexes) could contribute to higher As removal in experimental series with higher initial Fe(II) concentrations at the same initial Fe/As ratio. Simultaneous removal of soluble As and nitrate by anaerobic nitrate-reducing Fe(II)-oxidizing bacteria provides a feasible approach for in situ remediation of As-nitrate cocontaminated groundwater.

Simultaneous speciation analysis of inorganic arsenic, chromium and selenium in environmental waters by 3-(2-aminoethylamino) propyltrimethoxysilane modified multi-wall carbon nanotubes packed microcolumn solid phase extraction and ICP-MS

Speciation analysis of inorganic arsenic, chromium and selenium in environmental waters is of great significance for the monitoring of environmental pollution. In this work, 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) functionalized multi-wall carbon nanotubes (MWCNTs) were synthesized and employed as the adsorbent for simultaneous speciation analysis of inorganic arsenic, chromium and selenium in environmental waters by microcolumn solid-phase extraction (SPE)-inductively coupled plasma mass spectrometry (ICP-MS). It was found that As(V), Cr(VI) and Se(VI) could be selectively adsorbed on the microcolumn packed with AAPTS-MWCNTs adsorbent at pH around 2.2, while As(III), Cr(III) and Se(IV) could not be retained at this pH and passed through the microcolumn directly. Total inorganic arsenic, chromium and selenium was determined after the oxidation of As(III), Cr(III) and Se(IV) to As(V), Cr(VI) and Se(VI) with 10.0 μmol L(-1) KMnO4. The assay of As(III), Cr(III) and Se(IV) was based on subtracting As(V), Cr(VI) and Se(VI) from the total As, Cr and Se, respectively. Under the optimized conditions, the detection limits of 15, 38 and 16 ng L(-1) with the relative standard deviations (RSDs) of 7.4, 2.4 and 6.2% (c=1 µg L(-1), n=7) were obtained for As(V), Cr(VI) and Se(VI), respectively. The developed method was validated by analyzing four Certified Reference Materials, rainwater, Yangtze River and East Lake waters.