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.

Lability and bioavailability of Co, Fe, Pb, U and Zn in a uranium mining restoration site using DGT and phytoscreening.

Mine restoration is a long and ongoing process, requiring careful management, which must be informed by site-specific, geochemical risk assessment. Paired topsoil and tree core samples from 4 sites within the uranium mining complex of INB Caldas in Minas Gerais (Brazil) were collected. Soil samples were analysed for their total content of Co, Fe, Pb, U and Zn by XRF, and subsequently, the potential environmental bioavailability of these metals were investigated by DGT and pore water analysis. In addition, results were compared with metal concentrations obtained by Tree Coring from the forest vegetation. In all sampling areas, mean total concentrations of U (Ctot. = 100.5 ± 66.5 to 129.6 ± 57.1 mg kg-1), Pb (Ctot. = 30.8 ± 12.7 to 90.8 ± 90.8 mg kg-1), Zn (Ctot. = 91.5 ± 24.7 to 99.6 ± 10.3 mg kg-1) and Co (Ctot. = 73.8 ± 25.5 to 119.7 ± 26.4 mg kg-1) in soils exceeded respective quality reference values. Study results suggest that AMD caused the increase of labile concentrations of Zn in affected soils. The high lability of the elements Pb (R = 62 ± 34 to 81 ± 29%), U (R = 57 ± 20 to 77 ± 28%) and Zn (R = 21 ± 25 to 34 ± 31%) in soils together with high bioconcentration factors found in wood samples for Pb (BCF = 0.0004 ± 0.0003 to 0.0026 ± 0.0033) and Zn (BCF = 0.012 ± 0.013 to 0.025 ± 0.021) indicated a high toxic potential of these elements to the biota in the soils of the study site. The combination of pore water and DGT analysis with Tree Coring showed to be a useful approach to specify the risk of metal polluted soils. However, the comparison of the results from DGT and Tree Coring could not predict the uptake of metals into the xylems of the sampled tree individuals.

Intraspecific variation of trace elements in the kelp gull (Larus dominicanus): influence of age, sex and location.

Hepatic tissue of Larus dominicanus sampled on the coastline of the state of Santa Catarina in Brazil between October 2016 and May 2018 was used to evaluate intraspecific trends and spatial distribution of essential trace elements (Mn, Co, Cu, Zn, Mo and Cr) and non-essential trace elements (As, Pb, Cd, Hg, Ba and V). Principal Component Analysis (PCA) indicated differences in the bioaccumulation of trace elements between female adults and male adults, differences to sex and age were indicated by Kruskal-Wallis test. Heat maps suggest hot spots in locals with high concentration of trace elements in liver of Larus dominicanus. In general, the concentration of trace elements were comparable with values reported in other studies carried out for this species in South America and other regions of the world. The heat maps showed to be a promising tool to identify influences of the locality on bioaccumulation of trace elements in Larus dominicanus.

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.