Tissue Distribution of Mercury and Its Relationship with Selenium in Atlantic Bluefin Tuna (Thunnus thynnus L.)

Mercury (Hg) is an important heavy metal to consider in marine predators, while selenium (Se) has a natural antagonistic effect on this metal in fish. The Atlantic bluefin tuna (ABFT, Thunnus thynnus) is a pelagic top-level predator of the trophic web and their Hg muscular content is an object of concern in food safety. Nevertheless, little is known about levels of this metal in remaining tissues, which may be important as by-product source, and its relationship with Se. Thus, concentration of both elements in liver, kidney, brain, gill and bone, in addition to muscle, of ABFT were determined. The kidney was the tissue with the highest concentration of Hg (Total-Hg, THg) and Se, and the Se/THg concentration ratio was similar in all tissues, except bone and muscle. The Selenium Health Benefit Value (HBVSe) was positive in each specimen and tissue, indicating that the Se plays an important role against Hg not only in the muscle.

Non-Destructive Mercury Exposure Assessment in the Brandt's Hedgehog (Paraechinus Hypomelas): Spines As Indicators of Endogenous Concentrations

Due to its persistence, bioaccumulation characteristics and toxicity, environmental contamination with mercury (Hg) is of high concern for human health, living organisms and ecosystems, and its biological monitoring is highly relevant. In this study, the levels of total Hg were measured in organs, tissues and spines of 50 individuals of Brandt's hedgehog collected in Iran in 2019. The Hg median levels in kidneys, liver, muscle, and spines were 156, 47, 47 and 20 ng/g dry weight, respectively. The results showed a significant positive correlation between the levels of Hg in kidneys and liver (r = 0.519; p < 0.01) and in spines and muscle (r = 0.337, p < 0.01) and kidneys (r = 0.309, p < 0.05). Significant differences (p < 0.05) in Hg levels in organs and tissues were also observed depending on the sex, weight, length, and age of the individuals. In addition, the median levels of total Hg in kidneys of Brandt's hedgehogs from an agricultural ecotype were significantly higher (p < 0.05) than those collected from a forest ecotype, suggesting that the habitat could have a significant impact on animal contamination.

Different Mercury Species Partitioning and Distribution in the Water and Sediment of a Eutrophic Estuary in Northern Taiwan

The total Hg and methyl Hg in waters and sediments, as well as particulate total Hg (PTHg), were analyzed to study their distribution and partitioning in the Danshuei River Estuary (DRE), northern Taiwan. TOC and grain size were also determined in the sediment samples. The dissolved total Hg (DTHg) in waters ranged from 24.0 to 45.8 ng/L. The dissolved methyl Hg (DMeHg) concentrations contributed 0.6–30.4% of the DTHg pool, with the higher percentage appearing in the upper estuary. The DMeHg concentration positively correlated with the Chl.a within the estuary, suggesting that phytoplankton plays an important role in influencing the DMeHg concentration. The partitioning results indicated that DTHg chiefly dominates the THg (DTH + PTHg) pool, especially at a salinity of >15 psu region. The value of partition coefficient, log(KD), was within a range of 3.54 to 4.68, and the value linearly decreased with increasing salinity. The sediment total Hg (STHg) concentrations ranged from 80 to 379 ng/g, and most data exceeded the NOAA guidelines value (ERL < 150 ng/g), indicating that the DRE is contaminated with Hg. The STHg concentrations inversely and positively correlated with the grain size and TOC content, respectively, suggesting that sediment Hg distributions are strongly influenced by the both parameters.

Legacy of Past Mining Activity Affecting the Present Distribution of Dissolved and Particulate Mercury and Methylmercury in an Estuarine Environment (Nalón River, Northern Spain)

At the Nalón River estuary (Asturias, Northern Spain), the occurrence of Hg is due to historical mining activity which has resulted in environmental issues of great concern. Although several studies have investigated the sediment compartment regarding Hg contamination, no information is currently available on the fate of Hg and MeHg in the water column. Considering different hydrodynamic/seasonal conditions, water samples were collected along the estuary to evaluate Hg and MeHg distribution and partitioning behaviour between solid and aqueous phases. The complementary effect of the river discharge and tidal currents contributed to the prevalence of the dissolved (4.02 ± 1.33 ng L−1) or particulate (8.37 ± 4.20 ng L−1) Hg under different conditions of discharge in summer and autumn, respectively. Conversely, particulate MeHg prevailed when the river flow was low, especially at the estuary mouth (25.8 ± 19.1 pg L−1) and most likely due to the resuspension of fine particles promoted by a stronger tidal current. In comparison with the total Hg concentration, extremely low amounts of dissolved and particulate MeHg were observed, and strong interactions between MeHg and organic carbon highlighted a negligible risk of increased mobility and potential bioaccumulation of MeHg.

Kenaf (Hibiscus cannabinus L.) as a remedy to oxisol contaminated with different mercury (Hg2+) concentrations

We evaluated Hibiscus cannabinus (kenaf) to remedy oxisol contaminated with Hg2 + potential. The study was conducted in a controlled environment in pots with soil contaminated with HgCl2 solution, in a completely randomized design with 4 treatments: control (without Hg2+) and treatments with 5, 24 and 36 mg Hg2+ kg-1 of soil and 5 replicates / treatment. The quantification of total Hg in plant and soil samples was performed by atomic absorption spectrometry. Kenaf grown in contaminated pots did not show visual symptoms of toxicity. Plant height did not differ among treatments, but the dry shoot phytomass was 21.65% higher in control than the average of treatments with Hg. Treatment with 24 mg kg-1 showed dry root phytomass greater than control and the others. In general, oxisol was responsible for retaining greater amount of Hg than plants. Hg accumulated in greater proportion in roots than in shoots. In pots that received 36 mg kg-1, plants accumulated average of 2.57 mg kg-1 of Hg / pot, differing from the other treatments and the Hg transfer factor (TF) in plants was also calculated as the ratio of the concentration in shoots and in roots. The values were as follows: 3.11 for T1, 1.26 for T2, 0.05 for T3 and 0.02 for T4. Treatments showed no difference between T3 and T4 and TF decreased with increasing Hg dose. It could be concluded that Hg was more adsorbed by oxisol than by plants. Plants showed resistance to different soil Hg concentrations and can be considered as potential Hg2+ stabilizer

APPLICATION OF COUPLED HEC-HMS AND US EPA WASP FOR TRANSPORT MODELLING OF MERCURY IN THE MINING-IMPACTED AMBALANGA RIVER

This study provides a simulation of mercury (Hg) transport in water and sediments in the mining-impacted Ambalanga River located in Upper Agno Subbasin in the Philippines. The Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) and Water Quality Analysis Simulation Program (WASP) of the US Environmental Protection Agency (EPA) were coupled to handle both hydrologic modelling and total Hg transport processes, respectively, for 12 months in the year 2014. Watershed delineation from Digital Elevation Model, rainfall and streamflow data from the local weather bureau, and dam operational data were used to develop the hydrological model. The calibrated HEC-HMS model satisfactorily simulated the flow in the river and its tributaries, which is then used as an input to the Hg transport model. The Ambalanga subbasin was conceptually divided into 29 segments in WASP to represent the water column and the surface benthic sediment. Time-variable sediment and Hg load were applied to the upstream of Ambalanga River. Total Hg concentration in water and sediments at five sampling locations along the Ambalanga River and two sampling locations along the Upper Agno River were measured in 2014-2015, in addition to the Hg monitoring data from the local environmental bureau. The gathered data were used to validate the WASP model, and results show that it was able to reasonably simulate the Hg fate and transport. Simulation results showed a downward trend in Hg concentration in surface water and sediments from upstream to downstream, while Hg in sediments was observed to stabilize over time. The model was further utilized to come up with exceedance curves of Hg in water and sediments as a result of the river’s response to different Hg loading from the known point sources. The exceedance curves derived from the model were used to determine the maximum permissible Hg loading to the river and identify pollution load reduction measures for river rehabilitation.

Distributions of total mercury and methylmercury in dragonflies from a large abandoned mercury mining region in China

Dragonflies (Order Odonata) are often considered to be biosentinels of environmental contamination. Dragonflies (n = 439) belonging to 15 species of eight genera were collected from an abandoned mercury (Hg) mining region in China to investigate the bioaccumulation of total Hg (THg) and methylmercury (MeHg). The THg and MeHg concentrations in dragonflies varied widely within ranges of 0.06–19 mg/kg and 0.02–5.7 mg/kg, respectively. THg and MeHg were positively correlated with bodyweight (THg: r2 = 0.10, P = 0.000; MeHg: r2 = 0.09, P = 0.000). Significant variations were observed among species, with the highest MeHg value (in Orthetrum triangulare) being 5-fold higher than the lowest (in Pantala flavescens). These variations were consistent with those of nitrogen isotope (δ15N) values. A health risk assessment found hazard quotients for specialist dragonfly-consuming birds of up to 7.2, which is 2.4 times greater than the permissible limit of 3, suggesting a potential health risk of exposure.

Hg Concentrations and Stable Isotopes Variations in Tropical Fish Species of a Gold-mining Impacted Watershed in French Guiana

The aim of the study was to determine if gold mining activities could impact the mercury (Hg) concentrations and isotopic signatures in freshwater fish consumed by riparian people in French Guiana. Total Hg, MeHg concentrations and Hg stable isotopes ratios were analyzed in fish muscles from different species belonging to three feeding patterns (herbivorous, periphytophagous and piscivorous). We compared tributaries impacted by gold-mining activities (Camopi, CR) with a pristine area upstream (Trois-Sauts, TS), along the Oyapock River. We measured δ15N and δ13C to examine whether Hg patterns are due to differences in trophic level. Differences in δ15N and δ13C values between both studied sites were only observed for periphytophageous fish, with enriched values at TS. Total Hg concentrations and Hg stable isotopes fractionations showed that Hg accumulated in fish from both areas have undergone different biogeochemical processes. Δ199Hg variation in fish (-0.5 to 0.2‰) was higher than the ecosystem baseline defined by a Δ199Hg of -0.66‰ in sediments, and suggested limited aqueous photochemical MeHg degradation. Photochemistry-corrected δ202Hg in fish were 0.7‰ higher than the baseline, consistent with biophysical and chemical isotope fractionations in aquatic environment. While THg concentrations in periphytophagous fish were higher in the gold-mining area than in TS, in contrast to the sediments results, the ensemble of Hg isotope shifts did not allow to trace and quantify the gold-mining related liquid Hg(0) sources in the fish muscles.

Separation of methylmercury from biological samples for stable isotopic analysis

A new method of separation and pre-concentration of methylmercury (MeHg) species from total Hg in biological samples for determining the MeHg isotope composition.