Assessment of dissolved mercury by diffusive gradients in thin films devices in abandoned ponds impacted by small scale gold mining

Selenium-to-mercury ratios in popularly consumed Colombian fish: A comprehensive risk-benefit assessment

To understand the benefits and risks associated with the interaction between selenium (Se) and mercury (Hg), it is crucial to gather more information on the factors influencing the variability of their molar ratio. We analyzed Se and Hg concentrations, calculated selenium-to-mercury (Se:Hg) molar ratios, and assessed the health benefit values of selenium (HBV-Se) in commercially important fish (n = 309) from various aquatic environments in northern Colombia. Median Se concentrations were significantly higher (162.4 µg kg-1, U = 355, p = 0.01) compared to Hg concentrations (89.05 µg kg-1). Molar ratios values were greater than 1 for all 28 fish species, indicating a protective effect of Se against Hg. However, considerable variation in Se:Hg values was observed between species and sampling sites. All fish had Se:Hg values greater than 1 except for Astyanax magdalenae, Eugerres plumieri, Trachelyopterus sp. and Oreochromis niloticus. The HBV-Se values were also favorable (>1) for most species. Pelagic species had the lowest Hg concentrations (81.3 µg kg-1) but the highest Se:Hg ratios (6.4), while benthopelagic (908 µg kg-1, 5.2) and demersal species (712 µg kg-1, 3.7) showed higher Hg levels with lower Se:Hg values. There was a strong correlation between Hg levels, size (r2 = 0.94, p = 0.001) and trophic level of the fish (r2 = 0.99, p = 0.001). Similarly, Se levels showed a strong association with size (r2 = 0.96, p = 0.001) and trophic level (r2 = 0.94, p = 0.001). The findings of this study indicate that although the Se:Hg ratios suggest a protective action of Se against Hg toxicity, these values were not consistent. Variations in these ratios could have implications for assessing and managing risks associated with consuming Hg-contaminated fish. Therefore, it is crucial to continue evaluating health benefits and risks, especially in different ecosystems, including tropical ones.

Influence of environmental and biological factors on mercury accumulation in fish from the Atrato River Basin, Colombia

Understanding variations in total mercury (T-Hg) levels in fish is crucial for protecting aquatic biota and human health. This article evaluates the influence of environmental factors (temperature, pH) and biological variables (feeding habits, trophic level, total length, total weight), on T-Hg concentrations in fish from the Atrato River basin, Colombia. Utilizing a robust secondary data set of 842 fish samples from 16 species collected in 2019, we conducted a comprehensive analysis of these influences. We examined differences in T-Hg accumulation rates by habitat type (pelagic, benthopelagic and demersal) and probabilistically classified species based on their feeding habits and trophic levels. Our analysis identified a hierarchy of variables influencing T-Hg levels: feeding habits > total length > estimated total weight > trophic level > water temperature > pH, with temperature being the only predictor exerting a negative influence. Together, these variables accounted for over 60% of the variability in T-Hg accumulation in fish muscle tissue. Furthermore, fish in the Atrato River exhibited differential T-Hg based on habitat type, grouping into three distinct subpopulations stratified by feeding habits and trophic levels. These findings suggest that observed T-Hg accumulation patterns are driven by the functional ecology of the organisms, phenological characteristics, metabolism, contamination patterns, biogeography, land use, and the spatial and chemical configuration of the environmental matrices of the basin. Our results emphasize the importance of understand how biological and environmental factors influence T-Hg concentrations in fish, as these factors vary across aquatic systems. This knowledge is crucial for developing effective biodiversity management strategies. While we used a machine learning approach to identify key predictors of T-Hg accumulation, we also caution against potential biases in modeling T-Hg concentrations for aquatic biota management.

Plasma-engineered sugarcane bagasse: a novel strategy for efficient mercury removal from aqueous solutions

Metal ion adsorption using agro-industrial residues has shown promising results in remediating contaminated waters. However, adsorbent effectiveness relies on their properties, often necessitating processing for modification. Considering this, plasma treatment is effective in modifying material surfaces physically and chemically. This study investigated the modification of sugarcane bagasse (SB) using plasma treatment and evaluated its efficacy as a novel adsorbent for mercury removal from aqueous solutions. SB underwent low-temperature plasma treatment with sulfur hexafluoride (SF6) as the working gas, varying treatment times (2, 30, and 60 min), and fixed powers (80, 190, and 300 W) at 16 Pa pressure. Characterization via SEM/EDS, FTIR, XPS, and pHpzc revealed significant structural changes like increased in porosity and alteration in proportion atomic. Additionally, the successful incorporation of fluorine was confirmed in all treatment conditions, while sulfur was detected in only some samples. Amongst the tested conditions, the SB treated with 300 W for 60 min demonstrated the highest mercury removal efficiency, achieving an impressive 83.67% removal rate compared to untreated SB, which yielded only 57.95%. The adsorption mechanism exhibited both physical and chemical behavior, with chemisorption being the dominant process. The Freundlich model provided the best fit to the experimental data, with an R2 value of 0.97. In conclusion, plasma treatment can be a promising alternative for improving the physical and chemical characteristics of SB adsorbents, thereby improving their efficiency in removing mercury from aqueous solutions.

Biomonitoring of Mercury and Lead Levels in the Blood of Children Living near a Tropical River Impacted by Artisanal and Small-Scale Gold Mining in Colombia

(1) Background: Mercury and lead contamination resulting from various anthropogenic activities represents a global environmental problem and a considerable risk to the health of the human population. (2) Methods: The objective of this research was to evaluate the concentrations of mercury (Hg) and Lead (Pb) in the blood of the child population in the municipalities in the Atrato River basin using a direct Hg analyzer and graphite furnace atomic absorption spectrometry. (3) Results: In total, 171 children (5-14 years of age) were taken into account, and 18.71% (32) of the children had concentrations of Hg and Pb above the permissible values established by the WHO. In the municipality of UN, 19 children had blood Hg concentrations between 5.29 and 17.71 μg/L. In CA, two children had concentrations of 5.03 and 8.43 μg/L, separately. In the case of Pb, seven children showed concentrations between 3.60 and 4.83 μg/dL in the municipality of RQ, three in UN (3.59, 3.61, and 4.60 μg/dL), and one in Carmen de Atrato (5.47 μg/dL). (4) Conclusions: The levels of Hg and Pb in the blood of children living in the riparian areas of the Atrato River basin are related to gold mining activities in the basin and the consumption of contaminated fish.

Temporal mercury dynamics throughout the rice cultivation season in the Ebro Delta (NE Spain): An integrative approach

During the last few decades, inputs of mercury (Hg) to the environment from anthropogenic sources have increased. The Ebro Delta is an important area of rice production in the Iberian Peninsula. Given the industrial activity and its legacy pollution along the Ebro river, residues containing Hg have been transported throughout the Ebro Delta ecosystems. Rice paddies are regarded as propitious environments for Hg methylation and its subsequent incorporation to plants and rice paddies' food webs. We have analyzed how Hg dynamics change throughout the rice cultivation season in different compartments from the paddies' ecosystems: soil, water, rice plants and fauna. Furthermore, we assessed the effect of different agricultural practices (ecological vs. conventional) associated to various flooding patterns (wet vs. mild alternating wet and dry) to the Hg levels in rice fields. Finally, we have estimated the proportion of methylmercury (MeHg) to total mercury in a subset of samples, as MeHg is the most bioaccumulable toxic form for humans and wildlife. Overall, we observed varying degrees of mercury concentration over the rice cultivation season in the different compartments. We found that different agricultural practices and flooding patterns did not influence the THg levels observed in water, soil or plants. However, Hg concentrations in fauna samples seemed to be affected by hydroperiod and we also observed evidence of Hg biomagnification along the rice fields' aquatic food webs.

Evaluation of novel biomass-derived materials as binding layers for determining labile mercury in water by diffusive gradient in thin-films technique

In this work, several binding gels were successfully prepared in Diffusive Gradient in Thin-film (DGT) that targeted the inclusion of novel biomass-derived materials for the determination of the labile fraction of mercury (Hg) in water. First, five biomass-derived materials were tested and the descending order as a function of the average percentage of Hg removal in solution was feathers > biochar > cork > canola meal > rice husk. The best two materials were treated and pulverized into powder to be embedded in a hydrogel; and so, feathers were pyrolyzed preserving the sulfur contained in their keratin structure (FBC), and biochar (BC) was modified and pyrolyzed with sublimated sulfur (SBC) to increase the Hg sorption sites in its structure. Analysis by Energy Dispersive X-ray fluorescence (EDXRF) spectrometry confirmed that the different pyrolysis procedures increased sulfur absorption successfully. The efficiency of the new gels (BC, SBC and FBC) in agarose was evaluated by comparative Hg uptake tests, showing a larger efficacy in the following order: SBC > BC > FBC. To assess the suitability of their application in freshwater environments, novel DGT devices were also evaluated to determine their diffusion coefficients (D). This test was conducted under controlled laboratory conditions, with particular focus on the potential competence of trace elements (Mn, Cu, Zn, Ni, Pb, Cd and As), which are commonly present in natural waters affected by mining. A stronger linear relationship between the Hg uptake by binding layers and the deployment time were obtained for the DGT devices with SBC (R2 = 0.948) vs. BC (R2 = 0.885). Therefore, the D obtained for Hg were 8.94 × 10-6 cm2 s-1 for DGT-SBC and 5.12 × 10-6 cm2 s-1 for DGT-BC devices at 25 °C, both within the same order of magnitude reported by previous studies. The good performance obtained by DGT-SBC devices is a promising result and indicates the potential for valorization of waste materials in the DGT technique.

The effect of Zostera noltei recolonization on the sediment mercury vertical profiles of a recovering coastal lagoon

Mercury's extreme toxicity and persistence in the environment justifies a thorough evaluation of its dynamics in ecosystems. Aveiro Lagoon (Portugal) was for decades subject to mercury effluent discharges. A Nature-based Solution (NbS) involving Zostera noltei re-colonization is being tested as an active ecosystem restoration measure. To study the effect of Zostera noltei on the sediment contaminant biogeochemistry, seasonal (summer/winter) sediment, interstitial water and labile mercury vertical profiles were made in vegetated (Transplanted and Natural seagrass meadows) and non-vegetated sites (Bare-bottom area). While no significant differences (p > 0.05) were observed in the sedimentary phase, Zostera noltei presence reduced the reactive/labile mercury concentrations in the top sediment layers by up to 40% when compared to non-vegetated sediment, regardless of season. No differences were found between vegetated meadows, highlighting the fast recovery of the contaminant regulation ecosystem function provided by the plants after re-colonization and its potential for the rehabilitation of historically contaminated ecosystems.

In-situ Diffusive Gradients in thin-films passive sampling coupled with ex-situ small-sized electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry as green and white method for the simultaneous determination of labile species of toxic elements in surface water

This study presents for the first time the coupling between in-situ Diffusive Gradient in Thin-film (DGT) passive sampling technique and ex-situ small-sized instrumentation based on electrothermal vaporization capacitively coupled plasma microtorch optical emission spectrometry (SSETV-μCCP-OES) for the simultaneous determination of Cd, Pb, Cu, Zn and Hg in surface water. Unique features of the DGT-SSETV-μCCP-OES are low power and low Ar consumption for plasma generation (15 W, 150 mL min^-1) and significant improvement of the detection limits following DGT passive sampling. The new method was validated in terms of river water analysis in comparison with graphite furnace atomic absorption spectrometry and thermal decomposition atomic absorption spectrometry. Combining the abilities of preconcentration by in-situ Chelex-DGT passive sampling with plasma microtorch equipped with a low resolution microspectrometer provided multielemental simultaneous determination with detection limits of (μg L^-1) 0.01 (Cd, Zn and Hg), 0.02 (Cu) and 0.07 (Pb) in water, at least one order of magnitude better than using grab sampling without preconcentration. It was possible the quantification of labile fraction of priority hazardous metals (Cd, Pb) in river water below the instrumental limits of detection (μg L^-1) of 0.12 and 0.80 obtained in SSETV-μCCP-OES without DGT sampling. The precision of the method was in the range 15.3-22.4% (combined uncertainty), while the accuracy was 95-103% and trueness of 27-33% (expanded uncertainty, k = 2). The DGT-SSETV-μCCP-OES coupling proved to be an ideal and powerful tool for surface water analysis in compliance with green and white analytical chemistry concepts. The application of the RGB-12 algorithm provided very good red/green (AGREEprep)/blue/white scores (%) of 100/80/98/93, determined primarily by in-situ DGT passive sampling, very good detection limits and cost-effective SSETV-μCCP-OES instrumentation.