Assessment of dietary Selenium and its role in Mercury fate in cultured fish rainbow trout with two sustainable aquafeeds.

This study enhances the current limited understanding of the interaction between mercury (Hg) and selenium (Se) species in fish. Rainbow trout (Oncorhynchus mykiss), a model aquaculture fish, was exposed to Hg and Se species through controlled dietary conditions. Over a 6-month feeding trial, the impact of dietary Se on Hg bioaccumulation in fish, including flesh, brain, and liver, was tracked. Twelve dietary conditions were tested, including plant-based diets (0.25 µgSe g-1) and tuna byproduct diets (0.25 µgHg g-1, 8.0 µgSe g-1) enriched with methylmercury and/or Se as selenite or selenomethionine. The tuna byproduct diet resulted in lower Hg levels than the plant-based diets, with muscle Hg content below the European Commission's safe threshold. This study highlights the significant impact of specific Se compounds in the diet, particularly from tuna-based aquafeed, on Hg bioaccumulation. These promising results provide a strong recommendation for future use of fisheries byproducts in sustainable aquafeeds.

A review on arsenic in the environment: bio-accumulation, remediation, and disposal.

Arsenic is a widespread serious environmental pollutant as a food chain contaminant and non-threshold carcinogen. Arsenic transfer through the crops-soil-water system and animals is one of the most important pathways of human exposure and a measure of phytoremediation. Exposure occurs primarily from the consumption of contaminated water and foods. Various chemical technologies are utilized for As removal from contaminated water and soil, but they are very costly and difficult for large-scale cleaning of water and soil. In contrast, phytoremediation utilizes green plants to remove As from a contaminated environment. A large number of terrestrial and aquatic weed flora have been identified so far for their hyper metal removal capacity. In the panorama presented herein, the latest state of the art on methods of bioaccumulation, transfer mechanism of As through plants and animals, and remediation that encompass the use of physicochemical and biological processes, i.e., microbes, mosses, lichens, ferns, algae, and macrophytes have been assessed. Since these bioremediation approaches for the clean-up of this contaminant are still at the initial experimental stages, some have not been recognized at full scale. Nonetheless, extensive research on these primitive plants as bio-accumulators can be instrumental in controlling arsenic exposure and rehabilitation and may result in major progress to solve the problem on a worldwide scale.

A review on arsenic in the environment: contamination, mobility, sources, and exposure.

Arsenic is one of the regulated hazard materials in the environment and a persistent pollutant creating environmental, agricultural and health issues and posing a serious risk to humans. In the present review, sources and mobility of As in various compartments of the environment (air, water, soil and sediment) around the World are comprehensively investigated, along with measures of health hazards. Multiple atomic spectrometric approaches have been applied for total and speciation analysis of As chemical species. The LoD values are basically under 1 µg L-1, which is sufficient for the analysis of As or its chemical species in environmental samples. Both natural and anthropogenic sources contributed to As in air, while fine particulate matter tends to have higher concentrations of arsenic and results in high concentrations of As up to a maximum of 1660 ng m-3 in urban areas. Sources for As in natural waters (as dissolved or in particulate form) can be attributed to natural deposits, agricultural and industrial effluents, for which the maximum concentration of 2000 µg L-1 was found in groundwater. Sources for As in soil can be the initial contents, fossil fuel burning products, industrial effluents, pesticides, and so on, with a maximum reported concentration up to 4600 mg kg-1. Sources for As in sediments can be attributed to their reservoirs, with a maximum reported concentration up to 2500 mg kg-1. It is notable that some reported concentrations of As in the environment are several times higher than permissible limits. However, many aspects of arsenic environmental chemistry including contamination of the environment, quantification, mobility, removal and health hazards are still unclear.

Reply to the comment on "New insights into the biomineralization of mercury selenide nanoparticles through stable isotope analysis in giant petrel tissues" by A. Manceau, J. Hazard. Mater. 425 (2021) 127922. doi: 10.1016/j.jhazmat.2021.127922.

In the comments reported by A. Manceau [1], relating to our recent paper on mercury (Hg) species-specific isotopic characterization in giant petrel tissues [2] two critical questions were raised. Firstly, according to A. Manceau, our method of extraction and isolation of nanoparticles was not able to efficiently isolate mercury selenide nanoparticles (HgSe NPs) and therefore the δ202Hg values measured are not species-specific, but rather δ202Hg of mixtures of complexes such as MeHgCys, Hg(Sec)4, and HgSe. Secondly, he suggests that our main findings showing that no isotopic fractionation is induced during the HgSe NPs biomineralization step from the precursor-demethylated species is erroneous because it contradicts the conclusion of two recent articles by A. Manceau and co-workers [3,4]. In this reply we defend our scientific findings and respectively respond to the questions and comments raised by A. Manceau.

Mercury speciation in Scottish raptors reveals high proportions of inorganic mercury in Scottish golden eagles (Aquila chrysaetos): Potential occurrence of mercury selenide nanoparticles.

Knowledge of the uptake and fate of mercury (Hg) compounds in biota is important in understanding the global cycling of Hg and its transfer pathways through food chains. In this study, we analysed total mercury (T-Hg) and methylmercury (MeHg) concentrations in 117 livers of Scottish birds of prey that were found across Scotland and submitted for post-mortem examination through the Raptor Health Scotland project between 2009 and 2019. Statistical comparisons focussed on six species (barn owl, Tyto alba; Eurasian common buzzard, Buteo buteo; golden eagle, Aquila chrysaetos; hen harrier, Circus cyaneus; Eurasian sparrowhawk, Accipiter nisus; and tawny owl, Strix aluco) and showed that golden eagles had a statistically lower fraction of MeHg compared to other raptor species. Further investigation using stable carbon and stable nitrogen isotope ratio measurements carried out for the golden eagles (n = 15) indicated that the increased presence of inorganic mercury (iHg) correlated with a marine influence on the primarily terrestrial diet. Additional bioimaging (n = 1) with laser ablation - inductively coupled plasma - mass spectrometry indicated the co-location of Hg and selenium (Se) within the liver tissue and transmission electron microscopy showed evidence of nanoparticles within the range of 10-20 nm. Further analysis using single particle - inductively coupled plasma - mass spectrometry (n = 4) confirmed the presence of Hg nanoparticles. Together, the evidence suggests the presence of mercury selenide (HgSe) nanoparticles in the liver of some golden eagles that, to our knowledge, has never been directly observed in terrestrial birds of prey. This study points to two alternative hypotheses: these golden eagles may be efficient at breaking down MeHg and form HgSe nanoparticles as a detoxification mechanism (as previously observed in cetaceans), or some golden eagles with elevated iHg may have accumulated these nanoparticles by foraging on stranded cetaceans or seabirds.

First Time Identification of Selenoneine in Seabirds and Its Potential Role in Mercury Detoxification.

Birds are principally exposed to selenium (Se) through their diet. In long-lived and top predator seabirds, such as the giant petrel, extremely high concentrations of Se are found. Selenium speciation in biota has aroused great interest in recent years; however, there is a lack of information about the chemical form of Se in (sea)birds. The majority of publications focus on the growth performance and antioxidant status in broilers in relation to Se dietary supplementation. The present work combines elemental and molecular mass spectrometry for the characterization of Se species in wild (sea)birds. A set of eight giant petrels (Macronectes sp.) with a broad age range from the Southern Ocean were studied. Selenoneine, a Se-analogue of ergothioneine, was identified for the first time in wild avian species. This novel Se-compound, previously reported in fish, constitutes the major Se species in the water-soluble fraction of all of the internal tissues and blood samples analyzed. The levels of selenoneine found in giant petrels are the highest reported in animal tissues until now, supporting the trophic transfer in the marine food web. The characterization of selenoneine in the brain, representing between 78 and 88% of the total Se, suggests a crucial role in the nervous system. The dramatic decrease of selenoneine (from 68 to 3%) with an increase of Hg concentrations in the liver strongly supports the hypothesis of its key role in Hg detoxification.

New insights into the biomineralization of mercury selenide nanoparticles through stable isotope analysis in giant petrel tissues.

Tiemannite (HgSe) is considered the end-product of methylmercury (MeHg) demethylation in vertebrates. The biomineralization of HgSe nanoparticles (NPs) is understood to be an efficient MeHg detoxification mechanism; however, the process has not yet been fully elucidated. In order to contribute to the understanding of complex Hg metabolism and HgSe NPs formation, the Hg isotopic signatures of 40 samples of 11 giant petrels were measured. This seabird species is one of the largest avian scavengers in the Southern Ocean, highly exposed to MeHg through their diet, reaching Hg concentrations in the liver up to more than 900 µg g-1. This work constitutes the first species-specific isotopic measurement (δ202Hg, Δ199Hg) of HgSe NPs in seabirds and the largest characterization of this compound in biota. Similar δ202Hg values specifically associated to HgSe (δ202HgHgSe) and tissues (δ202Hgbulk) dominated by inorganic Hg species were found, suggesting that no isotopic fractionation is induced during the biomineralization step from the precursor (demethylated) species. In contrast, the largest variations between δ202Hgbulk and δ202HgHgSe were observed in muscle and brain tissues. This could be attributed to the higher fraction of Hg present as MeHg in these tissues. Hg-biomolecules screening highlights the importance of the isotopic characterization of these (unknown) complexes.

Stability, preservation and storage of As(iii), DMA, MMA and As(v) in water samples.

Correct handling and preservation of water samples is crucial to ensure their integrity for arsenic speciation measurements. ISO TS 19620:2018 is a method for the determination of arsenic(iii) and arsenic(v) species in waters by liquid chromatography (LC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) or hydride generation atomic fluorescence spectrometry (HG-AFS). During the development of this method, a study was performed to establish the best practices for storage and preservation of samples to maintain the integrity of the arsenic speciation and stability. Four arsenic species were studied: arsenite (As(iii)), arsenate (As(v)), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in three different water types: deionised water, mineral water and natural river water. The effect of sample bottle material, light, storage temperature, and acidification were evaluated. When samples are acidified and refrigerated, they can reliably be stored for up to 12 weeks without significantly affecting the arsenic concentration and speciation. The sample bottle material and light had no affect on the speciation integrity or stability.

Arsenic accumulation and speciation in strawberry plants exposed to inorganic arsenic enriched irrigation.

The accumulation and transformation of arsenic species have been studied in the context of hydroponic cultivation of strawberry plants. Cultivation experiments have been performed by adding inorganic arsenic at concentrations of 10, 100 and 1000 µg L-1 via root irrigation. The total arsenic content was determined by Hydride Generation-Atomic Fluorescence Spectrometry (HG-AFS). The accumulation was dependent on the concentration of arsenic added to the irrigation and the arsenic species. Arsenic (III) accumulated at higher rates than arsenic (V). A greater accumulation of arsenic was found in roots (0.44-4.10 mg kg-1) than in stems (0.43-1.27 mg kg-1) and fruits (0.22-0.30 mg kg-1). The speciation results obtained by HPLC-HG-AFS analysis indicated that the addition of As(III) resulted in a partial methylation producing monomethyl arsenic (MMA) and dimethyl arsenic (DMA). After As(V) addition, only MMA was observed and this was accompanied with a notable reduction in the ratio of As(V) to As(III).

Methylmercury varies more than one order of magnitude in commercial European rice.

Rice is known to accumulate methylmercury (MeHg) in the rice grains. MeHg as a neurotoxin impacts on the human central nervous systems and especially on the developing brain. In this exploratory study, 87 commercial rice products sold in Europe, including nine baby-rice products, were analyzed for total Hg and MeHg content. MeHg concentration in all rice products investigated range from 0.11 to 6.45µgkg(-1) with an average value of 1.91±1.07µgkg(-1) and baby-rice is not significantly different from other rice products. Total Hg ranges from 0.53 to 11.1µgkg(-1) with an average of 3.04±2.07µgkg(-1). MeHg concentrations in all rice products studied in this work would not exceed the provisional tolerable weekly intake (PTWI). 30% of all commercial market rice products exceeded 10% of the PTWI calculated for toddlers or 13% of products for adults with rice based diet.

Direct online HPLC-CV-AFS method for traces of methylmercury without derivatisation: a matrix-independent method for urine, sediment and biological tissue samples.

Mercury (Hg) is a global pollutant which occurs in different species, with methylmercury (MeHg) being the critical compound due to its neurotoxicity and bioaccumulation through the food chain. Methods for trace speciation of MeHg are therefore needed for a vast range of sample matrices, such as biological tissues, fluids, soils or sediments. We have previously developed an ultra-trace speciation method for methylmercury in water, based on a preconcentration HPLC cold vapour atomic fluorescence spectrometry (HPLC-CV-AFS) method. The focus of this work is mercury speciation in a variety of sample matrices to assess the versatility of the method. Certified reference materials were used where possible, and samples were spiked where reference materials were not available, e.g. human urine. Solid samples were submitted for commonly used digestion or extraction processes to obtain a liquid sample for injection into the analytical system. For MeHg in sediment samples, an extraction procedure was adapted to accommodate MeHg separation from high amounts of Hg(2+) to avoid an overload of the column. The recovery for MeHg determination was found to be in the range of 88-104% in fish reference materials (DOLT-2, DOLT-4, DORM-3), lobster (TORT-2), seaweed (IAEA-140/TM), sediments (ERM(®)-CC580) and spiked urine and has been proven to be robust, reliable, virtually matrix-independent and relatively cost-effective. Applications in the ultra-trace concentration range are possible using the preconcentration up to 200 mL, while for higher MeHg-containing samples, lower volumes can be applied. A comparison was carried out between species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID-GC-ICP-MS) as the gold standard and HPLC-CV-AFS for biological tissues (liver, kidney and muscle of pilot whales), showing a slope of 1.008 and R (2) = 0.97, which indicates that the HPLC-CV-AFS method achieves well-correlated results for MeHg in biological tissues.

Determination of mercury in river water by diffusive gradients in thin films using P81 membrane as binding layer.

In this work, a device based on diffusive gradients in thin films (DGT) was evaluated for the determination of Hg(II) in river water. The DGT device was assembled with a cellulose phosphate ion exchange membrane (P81 Whatman) as a binding phase and agarose gel 1.5% (m/v) as a diffusive layer. Laboratory deployments showed that the binding of Hg(2+) ([Hg(DGT)]/[Hg(solution)]) by P81 membrane was more effective (97%) than the Chelex 100 resin (80%).The effect of ionic strength, pH and potential interfering ions on Hg binding with DGT׳s was investigated. The results showed no significant effect on the binding of Hg(II) at pH range from 3.5 to 8.5 and at an ionic strength range from 0.0005 to 0.1 mol L(-1). Uptakes of 50 µg L(-1) Hg(II) by P81 membrane were not affected by Fe, Mn, Zn, Cu, Ca and Mg at the concentration range of 200-1800 µg L(-1). Finally, the DGT device using the P81 as the binding layer was applied for in situ measurements of Hg in river water. For in situ measurements, the labile Hg concentration (from <2 to 13 ng L(-1)) was lower than 10% of the dissolved fraction (from 155 to 446 ng L(-1)).

Field comparison of manual and semi-automatic methods for the measurement of total gaseous mercury in ambient air and assessment of equivalence.

The manual and semi-automatic methods for the measurement of total gaseous mercury in ambient air have been compared in a field trial for the first time. The comparison results have shown that whilst the expected random scatter is present, there was no significant systematic bias between the two methods, whose operational differences have also been outlined and analysed in this work. Furthermore it has been observed that because variation in instrument sensitivity is largely random in nature there is little effect on the results of the comparison if the period between instrument calibrations is altered. When the manual and semi-automatic methods are compared according to guidelines produced by the European Commission the results presented here, taken together with other supporting evidence, strongly suggest that the two methods are equivalent.

Establishing SI traceability for measurements of mercury vapour.

The majority of measurements of mercury vapour, for example those to determine mass concentration in air, are currently ultimately traceable to the vapour pressure of mercury, usually via a bell-jar calibration apparatus. This allows a saturated concentration of mercury vapour in air to develop in a confined space in equilibrium with ambient conditions, from which a known mass of mercury can be removed for calibration purposes. Several empirical equations are available to describe the vapour pressure of mercury at a given temperature, but the agreement between them is not good, with data from different equations sometimes differing by 5% or more. In order to remove the dependence of mercury vapour measurement on these empirical equations, and to provide stability, comparability and coherence for mercury vapour measurements, this paper describes work undertaken to link directly mercury vapour measurements to standards of mass, and therefore to establish traceability for these measurements to the SI system of units. This has been achieved by measuring the mass output rate of a dynamic mercury vapour generator gravimetrically, and linking this to the expected mass concentration in the bell-jar apparatus. The SI traceable mercury vapour measurements have been shown to agree with the predicted output from the bell-jar, as defined by the most commonly used empirical mercury vapour pressure equation, within the uncertainty of the measurement.