Examination of in vivo mutagenicity of sodium arsenite and dimethylarsinic acid in gpt delta rats

Arsenic is a well-known human bladder and liver carcinogen, but its exact mechanism of carcinogenicity is not fully understood. Dimethylarsinic acid（DMAV） is a major urinary metabolite of sodium arsenite（i As~Ⅲ） and induces urinary bladder cancers in rats. DMAVand i As~Ⅲare negative in in vitro mutagenicity tests. However, their in vivo mutagenicities have not been determined. The purpose of present study is to evaluate the in vivo mutagenicities of DMAVand i As~Ⅲin rat urinary bladder epithelium and liver using gpt delta F344 rats.Ten-week old male gpt delta F344 rats were randomized into 3 groups and administered 0,92 mg/L DMAV, or 87 mg/L i As~Ⅲ（each 50 mg/L As） for 13 weeks in the drinking water. In the mutation assay, point mutations are detected in the gpt gene by 6-thioguanine selection（gpt assay） and deletion mutations are identified in the red/gam genes by Spi-selection（Spi-assay）. Results of the gpt and Spi-assays showed that DMAVand i As~Ⅲhad no effects on the mutant frequencies or mutation spectrum in urinary bladder epithelium or liver. These findings indicate that DMAVand i As~Ⅲare not mutagenic in urinary bladder epithelium or liver in rats.

Defect-enhanced photocatalytic removal of dimethylarsinic acid over mixed-phase mesoporous TiO2

Much attention has been paid to the pollutant dimethylarsenic acid(DMA),because of its high toxicity even at very low doses.Although TiO2 photocatalytic oxidation(PCO)is one of the few effective methods for treating DMA-containing water,the efficient decomposition of DMA and simultaneous removal of toxic arsenic species remains a significant but challenging task.Here,defective mesoporous TiO2 with mixed-phase structure was synthesized and used as both photocatalyst and adsorbent for DMA removal.Due to the reduced band-gap and enhanced separation of photogenerated charge carriers,the oxygen-deficient TiO2 nanostructures exhibited 4.2 times higher PCO efficiency than commercial TiO2(P25).More importantly,the high surface area of the mesoporous TiO2 provided sufficient active sites for in-situ adsorption and reaction,resulting in the efficient removal of as-formed As(V).Combining the experimental and characterization results,the different roles of reactive species during PCO reactions were clarified.In the presence of hole(h+)as the dominant oxidation species,DMA was demethylated and transformed into MMA.Thereafter,MMA was subsequently reduced to As(Ⅲ)by photo-generated electrons.Superoxide radicals(O2·-)played a significant role in oxidizing As(Ⅲ)into As(Ⅴ),which was finally adsorptively removed by the mesoporous TiO2.

Effects of Dietary Intake of Arsenosugars and Other Organic Arsenic Species on Studies of Arsenic Methylation Efficiency in Humans

Extensive research has used dimethylarsinic acid(DMA)in urine as a marker of arsenic methylation.The premise is that humans methylate inorganic arsenicals to monomethylarsonic acid(MMA)and DMA and excrete these arsenic species into the urine.However,DMA in urine not only comes from the methylation of inorganic arsenic but also could be a result of metabolism of other arsenic species,such as arsenosugars and arsenolipids.Most environmental health and epidemiological studies of arsenic methylation might have overlooked confounding factors that contribute to DMA in urine.Here we critically evaluate reported studies that used methylation indexes,concentration ratios of methylated arsenicals,or the percentage of DMA in urine as markers of arsenic methylation efficiency.Dietary intake of arsenosugars potentially confounds the calculation and interpretation of the arsenic methylation efficiencies.Many studies have not considered incidental dietary intake of arsenosugars,arsenolipids,and other organic arsenic species.Future studies should consider the dietary intake of diverse arsenic species and their potential effect on the urinary concentrations of DMA.

Effect of Silicon on Arsenic Concentration and Speciation in Different Rice Tissues

Rice is a major source of inorganic arsenic(As) exposure for billions of people worldwide. Therefore, strategies to reduce As accumulation in rice should be adopted. Silicon(Si) application can effectively mitigate As accumulation in rice. In this study, a pot experiment was performed to investigate the effect of Si on As speciation and distribution in different rice tissues. The results showed that Si addition significantly increased As and Si concentrations in soil solution and Si concentration in iron plaque formed around rice root surface, whereas As in the iron plaque was significantly decreased. Total As concentrations in the stem, leaf, husk, and brown rice were remarkably decreased by 51.9%, 31.9%, 33.8%, and 24.1%, respectively, after Si addition, and inorganic As concentrations were reduced by 52.3%, 35.5%, 50.1%, and 20.1%, respectively. Moreover, both dimethylarsinic acid concentration and percentage in rice grain were significantly elevated by Si application. Therefore, Si application is promising as a way to mitigate inorganic As accumulation in rice and to reduce consumer health risk.

Effects of water management on arsenic and cadmium speciation and accumulation in an upland rice cultivar

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic（As） and cadmium（Cd） in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3–16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid（from 11.3% to 61.7%） made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal（loid）s in the grain of rice grown in soils polluted with both As and Cd.