The aim of this study was to evaluate the health risk of arsenic exposure by consumption of rice and its products marketed in northwestern Mexico. Sixty-six national and imported rice products were purchased in markets in northwestern Mexico, an endemic arsenic region. Total and inorganic arsenic in rice samples were analysed by inductively coupled plasma atomic emission spectroscopy and the risk assessment was evaluated according to the hazard quotient (HQ) and carcinogenic risk (CR). Total and inorganic arsenic in rice samples ranged from 0.06 to 0.29 mg/kg and from 0.03 to 0.13 mg/kg, respectively, and 40% of the analysed samples exceeded FAO/WHO arsenic recommended levels. The inorganic/total arsenic ratio ranged from 15% to 65%. The HQ and CR values for total and inorganic arsenic did not exceed safety levels. Therefore, rice supply in the northwestern of Mexico appears to be safe for human consumption.

Arsenic presence in the water has become one of the most concerning environmental problems. Electrocoagulation is a technology that offers several advantages over conventional treatments such as chemical coagulation. In the present work, an electrocoagulation system was optimized for arsenic removal at initial concentrations of 100 µg/L using response surface methodology. The effects of studied parameters were determined by a 2³ factorial design, whereas treatment time had a positive effect and current intensity had a negative effect on arsenic removal efficiency. With a p-value of 0.1629 and a confidence of level 99%, the type of electrode material did not have a significant effect on arsenic removal. Efficiency over 90% was reached at optimal operating conditions of 0.2 A of current intensity, and 7 min of treatment time using iron as the electrode material. However, the time necessary to accomplish with OMS arsenic guideline of 10 µg/L increased from 7 to 30 min when real arsenic-contaminated groundwater with an initial concentration of 80.2 ± 3.24 µg/L was used. The design of a pilot-scale electrocoagulation reactor was determined with the capacity to meet the water requirement of a 6417 population community in Sonora, Mexico. To provide the 1.0 L/s required, an electrocoagulation reactor with a working volume of 1.79 m³, a total electrode effective surface of 701 m², operating at a current intensity of 180 A and an operating cost of 0.0208 US$/day was proposed. Based on these results, electrocoagulation can be considered an efficient technology to treat arsenic-contaminated water and meet the drinking water quality standards. GRAPHICAL ABSTRACT

Many studies provide evidence relating lower human arsenic (As) methylation efficiency, represented by high percent urinary monomethylarsonic acid (MMA(V)), with several As-induced diseases, possibly due to the fact that MMA(V) serves as a proxy for MMA(III), the most toxic As metabolite. Some epidemiological studies suggested that indigenous Americans (AME) methylate As more efficiently; however, data supporting this have been equivocal. The aim of this study was to characterize the association between AME ancestry and As methylation efficiency using a panel of ancestry informative genetic markers to determine individual ancestry proportions in an admixed population (composed of two or more isolated ancestral populations) of 746 individuals environmentally exposed to As in northwest Mexico. Total urinary As (TAs) mean and range were 170.4 and 2.3–1053.5 μg/L, while percent AME (%AME) mean and range were 72.4 and 23–100. Adjusted (gender, age, AS3MT 7388/M287T haplotypes, body mass index [BMI], and TAs) multiple regression model showed that higher AME ancestry is significantly associated with lower percentage of urinary As excreted as MMA(V) (%uMMA) in this population (p < .01). Data also demonstrated a significant interaction between BMI and gender, indicating negative association between BMI and %uMMA, stronger in women than men (p < .01). Moreover, age and the AS3MT variants 7388 (intronic) and M287T (nonsynonymous) were also significantly associated with As methylation efficiency (p < .01). This study highlights the importance of BMI and indigenous American ancestry in some of the observed variability in As methylation efficiency, underscoring the need to be considered in epidemiology studies, particularly those carried out in admixed populations.