Laura Hinojosa Reyes

Simultaneous extraction of arsenic and selenium species from rice products by microwave-assisted enzymatic extraction and analysis by ion chromatography-inductively coupled plasma-mass spectrometry.

A microwave-assisted enzymatic extraction (MAEE) method was developed for the simultaneous extraction of arsenic (As) and selenium (Se) species in rice products. The total arsenic and selenium content in the enzymatic extracts were determined by inductively coupled plasma mass spectrometry (ICP-MS), while the speciation analysis was performed by ion chromatography coupled to inductively coupled plasma-mass spectrometry (IC-ICP-MS). The main factors affecting the enzymatic extraction process were evaluated in NIST SRM-1568a rice flour. The optimum extraction conditions were 500 mg of sample, 50 mg of protease XIV, and 25 mg of alpha-amylase in aqueous medium during 40 min at 37 degrees C. The extraction recoveries of total As and Se reached 100 +/- 3 and 80 +/- 4%, respectively. The species stability study during the MAEE process did not show transformation of the target species in rice products. The results of As speciation obtained for SRM-1568a were in agreement with previous studies of As speciation performed on the same reference material. The proposed method was applied to the determination of As and Se species in rice and rice-based cereals. Arsenite [As(III)], arsenate [As(V)], dimethylarsinic acid (DMA), and selenomethionine (SeMet) were the predominant species identified in rice products.

Coupling of solar photoelectro-Fenton with a BDD anode and solar heterogeneous photocatalysis for the mineralization of the herbicide atrazine.

Here, the synergetic effect of coupling solar photoelectro-Fenton (SPEF) and solar heterogeneous photocatalysis (SPC) on the mineralization of 200mL of a 20mg L(-1) atrazine solution, prepared from the commercial herbicide Gesaprim, at pH 3.0 was studied. Uniform, homogeneous and adherent anatase-TiO2 films onto glass spheres of 5mm diameter were prepared by the sol-gel dip-coating method and used as catalyst for SPC. However, this procedure yielded a poor removal of the substrate because of the low oxidation ability of positive holes and OH formed at the catalyst surface to destroy it. Atrazine decay was improved using anodic oxidation (AO), electro-Fenton (EF), SPEF and coupled SPEF-SPC at 100mA. The electrolytic cell contained a boron-doped diamond (BDD) anode and H2O2 was generated at a BDD cathode fed with an air flow. The removal and mineralization of atrazine increased when more oxidizing agents were generated in the sequence AO<EF<SPEF<coupled SPEF-SPC. Organics were destroyed by OH formed from water oxidation at the BDD anode in AO, along with OH formed from Fentons reaction between added Fe(2+) and generated H2O2 in EF. In SPEF, solar radiation produced higher amounts of OH induced from the photolysis of Fe(III) species and photodecomposed intermediates like Fe(III)-carboxylate complexes. The synergistic action of sunlight in the most potent coupled SPEF-SPC was ascribed to the additional quick removal of several intermediates with the oxidizing agents formed at the TiO2 surface. After 300min of this treatment, 80% mineralization, 9% mineralization current efficiency and 1.93kWhg(-1) TOC energy cost were obtained. The mineralization of atrazine was inhibited by the production of cyanuric acid, which was the main byproduct detected at the end of the coupled SPEF-SPC process.

Contamination and chemical fractionation of heavy metals in street dust from the Metropolitan Area of Monterrey, Mexico

The prevalence of heavy metal pollution and mobility of both Pb and Cd was investigated in street dust samples from the Metropolitan Area of Monterrey (MAM) in northern Mexico. Street dust samples from 30 selected sites were analysed for their content of Zn, Cd, Pb, Cr and Ni after digestion according to US EPA Method 3051. Multivariate analysis including correlation coefficient analysis, Principal Component Analysis and Cluster Analysis was used to analyse the data and identify possible sources of these heavy metals. Compared with background values, elevated concentrations of Pb (300 mg kg−1), Cd (7.6 mg kg−1) and Cr (78 mg kg−1) were observed in street dust of MAM. Based on multivariate statistical approaches, the studied elements were classified in three main sources: (1) Cr, Ni and Zn mainly derived from industrial activities; (2) Cd originating from traffic‐related activities; and (3) Pb associated with vehicular emissions. A sequential extraction procedure using the Tessier method was applied to evaluate the mobility of Pb and Cd in street dust. The majority of Pb was associated with the residual fraction followed by the carbonate fraction. The majority of Cd was associated with the residual fraction. These results indicated that the mobility was higher in Pb (26%) compared with Cd (11%), posing a potential risk to the environment.

A PRELIMINARY STUDY OF THE DISTRIBUTION AND MOBILITY OF MERCURY IN WATER AND SEDIMENTS FROM THE SAN JUAN RIVER WATERSHED, NUEVO LEON MEXICO

Monitoring of distribution and fractionation of mercury (Hg) from within the San Juan River Basin that provides water for the Metropolitan Area of Monterrey, Mexico (MAM), was performed. The purpose of this work was to characterize the risk of Hg exposure to human populations that reside in communities nearby the area. Total Hg was quantified from water and surface sediments (0-10 cm) collected from 11 locations during the summer season of 2006. The analysis of Hg was carried out by Cold Vapor Atomic Absorption Spectroscopy (CVAAS). Simultaneously, some relevant physical and chemical parameters were analyzed in water samples and correlated to Hg concentrations to trace the fate of Hg in the watershed. In the river water samples, Hg levels were in the range from 0.17 to 1.14 μg/L. The mean concentration level of Hg in sediment samples was 0.405±0.074 mg/Kg and showed a uniform Hg distribution along the San Juan River Basin, conversely, the fractionation studies showed that chemical speciation plays an important role in stability and low mobility.