A simple, green and low-cost agarose-based binding layer for simultaneous determination of cations and anions in aquatic systems using DGT.

The diffusive gradients in thin films (DGT) technique pre-concentrates labile species of trace elements, giving time-integrated in situ information about their labile concentrations. All previous DGT approaches for simultaneous uptake of cations and anions have used the hazardous polyacrylamide reagent to immobilize the binding phase. The present work proposes a diffusive layer of agarose and a mixed binding layer of ZrO2 and Chelex 100 immobilized in an agarose hydrogel to simultaneously determine the labile concentration of cations (Mn, Co, Ni, Cu, Zn and Cd) and anions (V, As, Se, Mo and Sb) in aquatic systems. The use of both layers using agarose instead of carcinogenic polyacrylamide as the hydrogel significantly reduces the costs and simplifies the manufacturing process. The proposed device was evaluated through recovery tests, deployment curves and pH/ionic strength tests. The mixed binding layer was compared with commercially available DGT devices for in situ deployment in river water. The relationships between accumulated mass and time (24 h) was linear (r2 > 0.9) for all analytes. The diffusion coefficients obtained were consistent with the literature, ranging from 3.98 to 8.43 × 10-6 cm2 s-1. Except for Zn at pH 8.0, the obtained values of CDGT/Cbulk were within the range of 1.00 ± 0.2 for the studied range of pH and for most ionic strengths. However, at low ionic strength, the concentrations of Mn, Co, Ni, Zn, V and Mo were underestimated. The concentrations of trace elements determined in river water using the proposed devices agreed with the labile concentrations determined by using commercial devices.

Combining ultrafiltration and diffusive gradients in thin films techniques for speciation/fractionation of Cu and Zn in cytosol of liver of Nile tilapia (Oreochromis niloticus).

This work aims to evaluate the size and lability of Cu and Zn bound to proteins in the cytosol of fish liver of Oreochromis niloticus by employing solid-phase extraction (SPE), diffusive gradients in thin films (DGT), and ultrafiltration (UF). SPE was carried out using Chelex-100. DGT containing Chelex-100 as binding agent was employed. Analyte concentrations were determined by ICP-MS. Total Cu and Zn concentrations in cytosol (1 g of fish liver in 5 ml of Tris-HCl) ranged from 39.6 to 44.3 ng ml-1 and 1498 to 2106 ng ml-1, respectively. Data from UF (10-30 kDa) suggested that Cu and Zn in cytosol were associated with ∼70% and 95%, respectively, with high-molecular-weight proteins. Cu-metallothionein was not selectively detected (although 28% of Cu was associated with low-molecular-weight proteins). However, information about the specific proteins in the cytosol will require coupling UF with organic mass spectrometry. Data from SPE showed the presence of labile Cu species of ∼17%, while the fraction of labile Zn species was >55%. However, data from DGT suggested a fraction of labile Cu species only of 7% and a labile Zn fraction of 5%. This data, as compared with previous data from literature, suggests that the DGT technique gave a more plausible estimation of the labile pool of Zn and Cu in cytosol. The combination of results from UF and DGT is capable of contributing to the knowledge about the labile and low-molecular pool of Cu and Zn.

In situ fractionation and redox speciation of arsenic in soda lakes of Nhecolândia (Pantanal, Brazil) using the diffusive gradients in thin films (DGT) technique.

In situ fractionation and redox speciation of As in three different saline-alkaline lakes (green, black and crystalline lakes) in the Pantanal of Nhecolândia (Brazil) were performed by using Diffusive Gradients in Thin films (DGT). The results indicated that As is present mainly in dissolved form. Total As concentration was similar when using different filter membranes, demonstrating that the species adsorbed by DGT devices were <10 kDa. Higher concentrations of labile total As were observed in the center of the lakes, indicating that the nature of the organic matter influences the formation of As complexes. Total As concentrations determined by using ZrO2 DGT were consistent with As concentration in ultrafiltered water samples collected in the black lake. However, part of the data about As(III) obtained in grab samples contrasted with DGT results. The differences observed may indicate that alterations in the species occur during the storage period before analysis by ultrafiltration. As(III) concentrations measured by DGT in the black and crystalline lakes were 1-3 µg L-1 and 4-7 µg L-1, respectively, accounting for only 4%-8% of the total DGT inorganic As. In the green lake, As(III) concentrations were significantly higher at the center (217 µg L-1). Both the phytoplankton community and the dissolved organic carbon influence the As speciation and bioavailability in the lakes of Nhecolândia. The DGT approach used in the present work was able to perform As speciation and demonstrates that in situ sampling analytical techniques are essential in understanding As speciation and its behavior in complex natural aquatic systems.

In situ arsenic speciation at the soil/water interface of saline-alkaline lakes of the Pantanal, Brazil: A DGT-based approach.

Arsenic (As) is a naturally occurring element in the Earth's crust, exhibiting toxicity towards a wide range of living organisms. Its properties and environmental dynamics are strongly regulated by its speciation, and the species As(III) and As(V) are the most commonly found in environmental systems. Recently, high concentrations of As were found in saline-alkaline lakes of the Pantanal (Brazil), which is the largest wetland area in the world. Therefore, we evaluated As contamination and its redox speciation (As(III) and As(V)) at the soil/water interface of biogeochemically distinct saline-alkaline lakes of Pantanal wetlands (Brazil). Both conventional sampling and in situ diffusive gradients in thin films (DGT) technique were employed. Zirconium oxide and 3-mercaptopropyl were used as ligand phases in DGT to selectively bind As species. High concentrations of total dissolved As in a shallow water table were found (<2337.5 µg L-1), whereas levels in soils were up to 2.4 µg g-1. Distinct scenarios were observed when comparing speciation analysis through spot sampling and DGT. Considering spot sampling, As(V) was the main species detected, whereas As(III) was only detected in only a few samples (<4.2 µg L-1). Conversely, results obtained by DGT showed that labile As(III) dominated arsenic speciation at the soil/water interface with levels up to 203.0 µg L-1. Coupling DGT data and DGT induced fluxes in sediments and soils model allowed obtaining kinetic data, showing that the soil barely participated in the arsenic dynamics on the shore of the lakes, and that this participation depends on the evapoconcentration process occurring in the region. Therefore, soil acts like a nonreactive matrix depending on the natural concentration process. In addition, our results reinforced the different geochemical characteristics of the studied saline-alkaline lakes and highlights the importance of robust passive sampling techniques in the context of metal/metalloid speciation in environmental analysis.

Functionalized Mesoporous Silicon Nanomaterials in Inorganic Soil Pollution Research: Opportunities for Soil Protection and Advanced Chemical Imaging.

"Innovative actions towards a pollution free-planet" is a goal of the United Nations Environment Assembly (UNEA). Aided by both the Food and Agricultural Organisation (FAO) and its Global Soil Partnership under the 3rd UNEA resolution, a consensus from > 170 countries have agreed a need for accelerated action and collaboration to combat soil pollution. This initiative has been tasked to find new and improved solutions to prevent and reduce soil pollution, and it is in this context that this review provides an updated perspective on an emerging technology platform that has already provided demonstrable utility for measurement, mapping, and monitoring of toxic trace elements (TTEs) in soils, in addition to the entrapment, removal, and remediation of pollutant sources. In this article, the development and characteristics of functionalized mesoporous silica nanomaterials (FMSN) will be discussed and compared with other common metal scavenging materials. The chemistries of the common functionalizations will be reviewed, in addition to providing an outlook on some of the future directions/applications of FMSN. The use of FMSN in soil will be considered with some specific case studies focusing on Hg and As. Finally, the advantages and developments of FMSN in the widely used diffusive gradients-in-thin films (DGT) technique will be discussed, in particular, its advantages as a DGT substrate for integration with oxygen planar optodes in multilayer systems that provide 2D mapping of metal pollutant fluxes at submillimeter resolution, which can be used to measure detailed sediment-water fluxes as well as soil-root interactions, to predict plant uptake and bioavailability.

Hybrid treatment system for remediation of sugarcane vinasse.

The sugar and alcohol industries provide promising alternative energy sources to replace the use of petroleum derivatives. Vinasse is a byproduct of the alcoholic fermentation of various raw materials, and is used in the fertirrigation of sugarcane plantations. However, its excessive use leads to many soil and groundwater related problems, including toxicity to living organisms, acidification of soil and water, accumulation of heavy metals, and contamination of groundwater. The use of integrated systems, such as stabilization, filtration, and phytoremediation, have attracted interest in the treatment of wastewater from various sources, as these highly effective biogeochemical systems can reduce the pollutant concentrations in wastewater, thereby reducing its adverse effects. The aim of this work was to develop a hybrid treatment system to optimize the physical and chemical characteristics of vinasse so that it can be used as fertilizer for crops with a lower pollution impact. The results of this study validated the effectiveness of the proposed system and demonstrated positive modifications of vinasse.

In situ speciation of uranium in treated acid mine drainage using the diffusion gradients in thin films technique (DGT).

The exchange membranes P81 and DE81 and Chelex-100 resin were used to perform in situ speciation of uranium in treated acid mine drainage at the Osamu Utsumi mining site, Poços de Caldas city, Southeast Brazil. To investigate possible chemical modifications in the samples during analysis, the three ligands were deployed in situ and in a laboratory (in lab). The results obtained in situ were also compared to a speciation performed using Visual MINTEQ software. Chelex-100 retained total labile U for a period of up to 48 h. The labile U fraction determined by Chelex 100 ranged from 107 ± 6% to 147 ± 44% in situ and from 115 ± 22% to 191 ± 5% in lab. DE81 retained anionic U species up to 8 h, with labile fractions ranging from 37 ± 2% to 76 ± 3% in situ and 34 ± 12% to 180 ± 17% in lab. P81 exhibited a lower efficiency in retaining U species, with concentrations ranging from 6± 2% to 19± 2% in situ and 3± 2% to 18± 2% in lab. The speciation obtained from MINTEQ suggests that the major U species were UO2OH+, UO2(OH)3-, UO2(OH)2(aq), Ca2UO2(CO3)3(aq), CaUO2(CO3)32-, UO2(CO3)22-, and UO2(CO3)34-. This result is in accordance with the results obtained in situ. Differences concerning speciation and the total and soluble U concentrations were observed between the deployments performed in situ and in the laboratory, indicating that U speciation must be performed in situ.

In situ selective determination of methylmercury in river water by diffusive gradient in thin films technique (DGT) using baker's yeast (Saccharomyces cerevisiae) immobilized in agarose gel as binding phase.

Saccharomyces cerevisiae immobilized in agarose gel as binding phase and polyacrylamide as diffusive layer in the diffusive gradient in thin films technique (DGT) was used for selective determination of methylmercury (MeHg). Deployment tests showed good linearity in mass uptake up to 48 h (3276 ng). When coupling the DGT technique with Cold Vapor Atomic Fluorescence Spectrometry, the method has a limit of detection of 0.44 ng L(-1) (pre concentration factor of 11 for 48 h deployment). Diffusion coefficient of 7.03 ± 0.77 × 10(-6) cm(2) s(-1) at 23 °C in polyacrylamide gel (pH = 5.5 and ionic strength = 0.05 mol L(-1) NaCl) was obtained. Influence of ionic strength (from 0.0005 mol L(-1) to 0.1 mol L(-1) NaCl) and pH (from 3.5 to 8.5) on MeHg uptake were evaluated. For these range, recoveries of 84-105% and 84-98% were obtained for ionic strength and pH respectively. Potential interference due to presence of Cu, Fe, Mn, Zn was also assessed showing good recoveries (70-87%). The selectivity of the proposed approach was tested by deployments in solutions containing MeHg and Hg(II). Results obtained showed recoveries of 102-115 % for MeHg, while the uptake of Hg(II) was insignificant. The proposed approach was successfully employed for in situ measurements in the Negro River (Manaus-AM, Brazil).