Low arsenic bioaccessibility by fixation in nanostructured iron (Hydr)oxides: quantitative identification of As-bearing phases

A new analytical protocol was developed to provide quantitative, single-particle identification of arsenic in heterogeneous nanoscale mineral phases in soil samples, with a view to establishing its potential risk to human health. Microscopic techniques enabled quantitative, single-particle identification of As-bearing phases in twenty soil samples collected in a gold mining district with arsenic concentrations in range of 8 to 6354 mg kg. Arsenic is primarily observed in association with iron (hydr) oxides in fine intergrowth with phyllosilicates. Only small quantities of arsenopyrite and ferric arsenate (likely scorodite) particles, common in the local gold mineralization, were identified (e.g., 7 and 9 out, respectively, of app. 74,000 particles analyzed). Within the high-arsenic subgroup, the arsenic concentrations in the particle size fraction below 250μm ranges from 211 to 4304 mg kg. The bioaccessible arsenic in the same size fraction is within 0.86–22 mg kg (0.3–5.0%). Arsenic is trapped in oriented aggregates of crystalline iron (hydr)oxides nanoparticles, and this mechanism accounts for the low As bioaccessibility. The calculated As exposure from soil ingestion is less than 10% of the arsenic Benchmark Dose Lower Limit - BMDL. Therefore, the health risk associated with the ingestion of this geogenic material is considered to be low

Natural attenuation of arsenic in the environment by immobilization in nanostructured hematite

Iron (hydr)oxides are known to play a major role in arsenic fixation in the environment. The mechanisms for long-term fixation into their crystal structure, however, remain poorly understood, especially arsenic partitioning behavior during transformation from amorphous to crystalline phases under natural conditions. In this study, these mechanisms are investigated in Fe–Al-oxisols exposed over a period of 10 years to a sulfide concentrate in tailings impoundments. The spatial resolution necessary to investigate the markedly heterogeneous nanoscale phases found in the oxisols was achieved by combining three different, high resolution electron microscopy techniques – Nano-Beam Electron Diffraction (NBD), Electron Energy-Loss Spectroscopy (EELS), and High Resolution Transmission Electron Microscopy (HRTEM). Arsenic (1.6 ± 0.5 wt.%) was unambiguously and precisely identified in mesocrystals of Al-hematite with an As/Fe atomic ratio of 0.026 ± 0.006. The increase in the c-axis (c = 1.379 ± 0.009 nm) compared to standard hematite (c = 1.372 nm) is consistent with the presence of arsenic in the Al-hematite structure. The As-bearing Al-hematite is interpreted as a secondary phase formed from oxyhydroxides, such as ferrihydrite, during the long-term exposure to the sulfide tailings. The proposed mechanism of arsenic fixation in the Al-hematite structure involves adsorption onto Al-ferrihydrite nanoparticles, followed by Al-ferrihydrite aggregation by self-assembly oriented attachment and coalescence that ultimately produces Al-hematite mesocrystals. Our results illustrate for the first time the process of formation of stable arsenic bearing Al-hematite for the long-term immobilization of arsenic in environmental samples

Dietary arsenic exposure in Brazil: the contribution of rice and beans

The human health risk associated with arsenic in food in Southeast Brazil was quantified. Based on the most commonly consumed food types in the Brazilian diet, the maximum inorganic As (iAs) daily intake from food (0.255 μg kg body weight per day) is approximately 9% of the Benchmark Dose Lower Limit (BMDL) of 3 μg kg body weight per day set by the World Health Organization (WHO) and Food and Agriculture Organization (FAO) Joint Expert Committee in Food Additives (JECFA). When water is included, the contribution of food to the total intake varies from 96.9% to 39.7%. Rice and beans, the main Brazilian staple food, contribute between 67 and 90% of the total As intake from food (46–79% from rice and 11–23% from beans). The substantial contribution of beans to total As food intake is reported for the first time. The broad range of As concentrations in rice and beans highlights the variable and potentially large contribution of both to As food intake in places where diet consists largely of these two food categories

Arsenic entrapment by nanocrystals of Al-magnetite: The role of Al in crystal growth and As retention

The nature of As-Al-Fe co-precipitates aged for 120 days are investigated in detail by High Resolution Transmission Electron Microscopy (HRTEM), Scanning TEM (STEM), electron diffraction, Energy Dispersive X-Ray Spectroscopy (EDS), Electron Energy-Loss Spectroscopy (EELS), and Energy Filtered Transmission Electron Microscopy (EFTEM). The Al present in magnetite is shown to favour As incorporation (up to 1.10 wt%) relative to Al-free magnetite and Al-goethite, but As uptake by Al-magnetite decreases with increasing Al substitution (3.53-11.37 mol% Al). Arsenic-bearing magnetite and goethite mesocrystals (MCs) are formed by oriented aggregation (OA) of primary nanoparticles (NPs). Well-crystalline magnetite likely formed by Otswald ripening was predominant in the Al-free system. The As content in Al-goethite MCs (having approximately 13% substituted Al) was close to the EDS detection limit (0.1 wt% As), but was below detection in Al-goethites with 23.00-32.19 mol% Al. Our results show for the first time the capacity of Al-magnetite to incorporate more As than Al-free magnetite, and the role of Al in favouring OA-based crystal growth under the experimental conditions, and therefore As retention in the formed MCs. The proposed mechanism of As incorporation involves adsorption of As onto the newly formed NPs. Arsenic is then trapped in the MCs as they grow by self-assembly OA upon attachment of the NPs. We conclude that Al may diffuse to the crystal faces with high surface energy to reduce the total energy of the system during the attachment events, thus favouring the oriented aggregation

Latin American experiences in arsenic removal from drinking water and mining effluents

Due to increasing demand for potable and irrigation water, water suppliers have to use alternative resources. They either have to regenerate wastewater or deal with contaminated surface water. This book brings together the experiences of various experts in preparing of innovative materials that are selective for arsenic and chromium removal, and inventing some innovative processes to extract these elements from water. The book should be of high interest to engineers and decision-makers responsible for production and delivery of safe water. The book is divided into three parts. The first one shows the effect of arsenic and chromium ions on living organisms. The second one presents the studies on preparation of innovative materials with improved affinity towards arsenic as well as chromium. The third part shows the innovative methods for removal of these toxic elements, with special attention paid to chromatographic, membrane, and hybrid systems. The book is the first ever scientific work addressed to two most harmful elements appearing in water and provides a comprehensive review of materials and methods useful for making the water safe. The book discusses in detail the various fabrication techniques for sorbents and membranes that are now commercially available or appear in the development stage and will be commercialized in the next decades. Some of the technologies described in the third part will be implemented at the industrial scale in the future as wellPostprint (published version

Latin American experiences in arsenic removal from drinking water and mining effluents

Due to increasing demand for potable and irrigation water, water suppliers have to use alternative resources. They either have to regenerate wastewater or deal with contaminated surface water. This book brings together the experiences of various experts in preparing of innovative materials that are selective for arsenic and chromium removal, and inventing some innovative processes to extract these elements from water. The book should be of high interest to engineers and decision-makers responsible for production and delivery of safe water. The book is divided into three parts. The first one shows the effect of arsenic and chromium ions on living organisms. The second one presents the studies on preparation of innovative materials with improved affinity towards arsenic as well as chromium. The third part shows the innovative methods for removal of these toxic elements, with special attention paid to chromatographic, membrane, and hybrid systems. The book is the first ever scientific work addressed to two most harmful elements appearing in water and provides a comprehensive review of materials and methods useful for making the water safe. The book discusses in detail the various fabrication techniques for sorbents and membranes that are now commercially available or appear in the development stage and will be commercialized in the next decades. Some of the technologies described in the third part will be implemented at the industrial scale in the future as wel