First-Time Isotopic Characterization of Seleno-Compounds in Biota: A Pilot Study of Selenium Isotopic Composition in Top Predator Seabirds.

This study pioneers the reporting of Se isotopes in marine top predators and represents the most extensive Se isotopic characterization in animals to date. A methodology based on hydride generation─multicollector inductively coupled plasma mass spectrometry─was established for such samples. The study was conducted on various internal organs of giant petrels (Macronectes spp.), encompassing bulk tissues (δ82/78Sebulk), distinct Se-specific fractions such as selenoneine (δ82/78SeSEN), and HgSe nanoparticles (δ82/78SeNPs). The δ82/78Sebulk results (2.0-5.6‰) offer preliminary insights into the fate of Se in key internal organs of seabirds, including the liver, the kidneys, the muscle, and the brain. Notably, the liver of all individuals was enriched in heavier Se isotopes compared to other examined tissues. In nanoparticle fraction, δ82/78Se varies significantly across individuals (δ82/78SeNPs from 0.6 to 5.7‰, n = 8), whereas it exhibits remarkable consistency among tissues and individuals for selenoneine (δ82/78SeSEN, 1.7 ± 0.3‰, n = 8). Significantly, there was a positive correlation between the shift from δ82/78Sebulk to δ82/78SeSEN and the proportion of Se present as selenoneine in the internal organs. This pilot study proves that Se species-specific isotopic composition is a promising tool for a better understanding of Se species fate, sources, and dynamics in animals.

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.

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.

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.

Determination of the Intracellular Complexation of Inorganic and Methylmercury in Cyanobacterium Synechocystis sp. PCC 6803.

Understanding of mercury (Hg) complexation with low molecular weight (LMW) bioligands will help elucidate its speciation. In natural waters, the rate of this complexation is governed by physicochemical, geochemical, and biochemical parameters. However, the role of bioligands involved in Hg intracellular handling by aquatic microorganisms is not well documented. Here, we combine the use of isotopically labeled Hg species (inorganic and monomethylmercury, iHg and MeHg) with gas or liquid chromatography coupling to elemental and molecular mass spectrometry to explore the role of intracellular biogenic ligands involved in iHg and MeHg speciation in cyanobacterium Synechocystis sp. PCC 6803, a representative phytoplankton species. This approach allowed to track resulting metabolic and newly found intracellular Hg biocomplexes (e.g., organic thiols) in Synechocystis sp. PCC 6803 finding different intracellular Hg species binding affinities with both high and low molecular weight (HMW and LMW) bioligands in the exponential and stationary phase. Furthermore, the parallel detection with both elemental and molecular ionization sources allowed the sensitive detection and molecular identification of glutathione (GSH) as the main low molecular weight binding ligand to iHg ((GS)2-Hg) and MeHg (GS-MeHg) in the cytosolic fraction. Such a novel experimental approach expands our knowledge on the role of biogenic ligands involved in iHg and MeHg intracellular handling in cyanobacteria.

Species-specific isotope tracking of mercury uptake and transformations by pico-nanoplankton in an eutrophic lake.

The present study aims to explore the bioaccumulation and biotic transformations of inorganic (iHg) and monomethyl mercury (MMHg) by natural pico-nanoplankton community from eutrophic lake Soppen, Switzerland. Pico-nanoplankton encompass mainly bacterioplankton, mycoplankton and phytoplankton groups with size between 0.2 and 20 µm. Species-specific enriched isotope mixture of 199iHg and 201MMHg was used to explore the accumulation, the subcellular distribution and transformations occurring in natural pico-nanoplankton sampled at 2 different depths (6.6 m and 8.3 m). Cyanobacteria, diatoms, cryptophyta, green algae and heterotrophic microorganisms were identified as the major groups of pico-nanoplankton with diatoms prevailing at deeper samples. Results showed that pico-nanoplankton accumulated both iHg and MMHg preferentially in the cell membrane/organelles, despite observed losses. The ratios between the iHg and MMHg concentrations measured in the membrane/organelles and cytosol were comparable for iHg and MMHg. Pico-nanoplankton demethylate added 201MMHg (~4 and 12% per day depending on cellular compartment), although the involved pathways are to further explore. Comparison of the concentrations of 201iHg formed from 201MMHg demethylation in whole system, medium and whole cells showed that 82% of the demethylation was biologically mediated by pico-nanoplankton. No significant methylation of iHg by pico-nanoplankton was observed. The accumulation of iHg and MMHg and the percentage of demethylated MMHg correlated positively with the relative abundance of diatoms and heterotrophic microorganisms in the pico-nanoplankton, the concentrations of TN, Mg2+, NO3-, NO2-, NH4+ and negatively with the concentrations of DOC, K+, Na+, Ca2+, SO42-. Taken together the results of the present field study confirm the role of pico-nanoplankton in Hg bioaccumulation and demethylation, however further research is needed to better understand the underlying mechanisms and interconnection between heterotrophic and autotrophic microorganisms.

Mercury isotopes of key tissues document mercury metabolic processes in seabirds.

Seabirds accumulate significant amounts of mercury (Hg) due to their long-life span together with their medium to high trophic position in marine food webs. Hg speciation and Hg isotopic analyses of total Hg in different tissues (pectoral muscles, liver, brain, kidneys, blood and feathers) were assessed to investigate their detoxification mechanisms. Three species with contrasted ecological characteristics were studied: the Antarctic prion (zooplankton feeder), the white-chinned petrel (pelagic generalist consumer) and the southern giant petrel (scavenger on seabirds and marine mammals). The difference of mass-dependent fractionation (MDF, δ202Hg) values between liver and muscles (up to 0.94 ‰) in all three seabirds strongly suggests hepatic demethylation of the isotopically lighter methylmercury (MeHg) and subsequent redistribution of the isotopically heavier fraction of MeHg towards the muscles. Similarly, higher δ202Hg values in feathers (up to 1.88 ‰) relative to muscles and higher proportion of MeHg in feathers (94-97%) than muscles (30-70%) likely indicate potential MeHg demethylation in muscle and preferential excretion of MeHg (isotopically heavier) in the growing feathers during moult. The extents of these key detoxification processes were strongly dependent on the species-specific detoxification strategies and levels of dietary MeHg exposure. We also found higher mass-independent fractionation (MIF, Δ199Hg) values in feathers relative to internal tissues, possibly due to different integration times of Hg exposure between permanently active organs and inert tissues as feathers. Hg isotope variations reported in this study show evidence of detoxification processes in seabirds and propose a powerful approach for deep investigation of the Hg metabolic processes in seabirds.

A "seabird-eye" on mercury stable isotopes and cycling in the Southern Ocean.

Since mercury (Hg) biogeochemistry in the Southern Ocean is minimally documented, we investigated Hg stable isotopes in the blood of seabirds breeding at different latitudes in the Antarctic, Subantarctic and Subtropical zones. Hg isotopic composition was determined in adult penguins (5 species) and skua chicks (2 species) from Adélie Land (66°39'S, Antarctic) to Crozet (46°25'S, Subantarctic) and Amsterdam Island (37°47'S, Subtropical). Mass-dependent (MDF, δ202Hg) and mass-independent (MIF, Δ199Hg) Hg isotopic values separated populations geographically. Antarctic seabirds exhibited lower δ202Hg values (-0.02 to 0.79 ‰, min-max) than Subantarctic (0.88 to 2.12 ‰) and Subtropical (1.44 to 2.37 ‰) seabirds. In contrast, Δ199Hg values varied slightly from Antarctic (1.31 to 1.73 ‰) to Subtropical (1.69 to 2.04 ‰) waters. The extent of methylmercury (MeHg) photodemethylation extrapolated from Δ199Hg values was not significantly different between locations, implying that most of the bioaccumulated MeHg was of mesopelagic origin. The larger increase of MDF between the three latitudes co-varies with MeHg concentrations. This supports an increasing effect of specific biogenic Hg pathways from Antarctic to Subtropical waters, such as Hg biological transformations and accumulations. This "biogenic effect" among different productive southern oceanic regions can also be related to different mixed layer depth dynamics and biological productivity turnover that specifically influence the vertical transport between the mesopelagic and the photic zones. This study shows the first Hg isotopic data of the Southern Ocean at large scale and reveals how regional Southern Ocean dynamics and productivity control marine MeHg biogeochemistry and the exposure of seabirds to Hg contamination.

Assessment of Hg contamination by a Chlor-Alkali Plant in riverine and coastal sites combining Hg speciation and isotopic signature (Sagua la Grande River, Cuba).

Chlor-alkali plants (CAP) are recognized as major sources of mercury (Hg) in the environment. In this work, Hg concentration, speciation and isotopic signature were determined in sediments and biota (fish and oyster) from Sagua La Grande River (SG River) and the adjacent coastal zone in the vicinity of a CAP (Cuba). High Hg concentrations in surface sediments (up to 5072 ng g-1), mainly occurring as inorganic Hg, decrease with the distance from the CAP along the SG River and seaward. Meanwhile, Hg concentration and speciation in riverine catfish (Claria gariepinus) muscle (1093 ± 319 ng g-1, ˜70% as MeHg) and coastal oysters (Crassostrea rizophorae) (596 ± 233 ng g-1, ˜50% as MeHg) indicate a direct impact from CAP. Hg isotopic signature in sediments, following both mass dependent (MDF) and mass independent fractionation (MIF), exhibits a clear binary mixing between CAP pollution (+0.42‰, δ202Hg; -0.18‰, Δ201Hg) and regional background end-member (˜ -0.49‰, δ202Hg; +0.01‰, Δ201Hg). The combination of speciation and isotopic information in biota and sediments allows to trace Hg contamination pathways from contaminated sediments to the biota, establishing the importance of both methylation and demethylation extent in both river and coastal sites before Hg species bioaccumulation.

Identification of sources and bioaccumulation pathways of MeHg in subantarctic penguins: a stable isotopic investigation.

Seabirds are widely used as bioindicators of mercury (Hg) contamination in marine ecosystems and the investigation of their foraging strategies is of key importance to better understand methylmercury (MeHg) exposure pathways and environmental sources within the different ecosystems. Here we report stable isotopic composition for both Hg mass-dependent (e.g. δ202Hg) and mass-independent (e.g. Δ199Hg) fractionation (proxies of Hg sources and transformations), carbon (δ13C, proxy of foraging habitat) and nitrogen (δ15N, proxy of trophic position) in blood of four species of sympatric penguins breeding at the subantarctic Crozet Islands (Southern Indian Ocean). Penguins have species-specific foraging strategies, from coastal to oceanic waters and from benthic to pelagic dives, and feed on different prey. A progressive increase to heavier Hg isotopic composition (δ202Hg and Δ199Hg, respectively) was observed from benthic (1.45 ± 0.12 and 1.41 ± 0.06‰) to epipelagic (1.93 ± 0.18 and 1.77 ± 0.13‰) penguins, indicating a benthic-pelagic gradient of MeHg sources close to Crozet Islands. The relative variations of MeHg concentration, δ202Hg and Δ199Hg with pelagic penguins feeding in Polar Front circumpolar waters (1.66 ± 0.11 and 1.54 ± 0.06‰) support that different MeHg sources occur at large scales in Southern Ocean deep waters.

Seabird Tissues As Efficient Biomonitoring Tools for Hg Isotopic Investigations: Implications of Using Blood and Feathers from Chicks and Adults.

Blood and feathers are the two most targeted avian tissues for environmental biomonitoring studies, with mercury (Hg) concentration in blood and body feathers reflecting short and long-term Hg exposure, respectively. In this work, we investigated how Hg isotopic composition (e.g., δ202Hg and Δ199Hg) of blood and feathers from either seabird chicks (skuas, n = 40) or adults (penguins, n = 62) can accurately provide information on exposure to Hg in marine ecosystems. Our results indicate a strong correlation between blood and feather Hg isotopic values for skua chicks, with similar δ202Hg and Δ199Hg values in the two tissues (mean difference: -0.01 ± 0.25 ‰ and -0.05 ± 0.12 ‰, respectively). Since blood and body feathers of chicks integrate the same temporal window of Hg exposure, this suggests that δ202Hg and Δ199Hg values can be directly compared without any correction factors within and between avian groups. Conversely, penguin adults show higher δ202Hg and Δ199Hg values in feathers than in blood (mean differences: 0.28 ± 0.19‰ and 0.25 ± 0.13‰), most likely due to tissue-specific Hg temporal integration. Since feathers integrate long-term (i.e., the intermoult period) Hg accumulation, whereas blood reflects short-term (i.e., seasonal) Hg exposure in adult birds, the two tissues provide complementary information on trophic ecology at different time scales.

Assessment of mercury speciation in feathers using species-specific isotope dilution analysis.

Seabirds are considered as effective sentinels of environmental marine contamination and their feathers are extensively used as non-lethal samples for contaminant biomonitoring. This tissue represents the main route for mercury (Hg) elimination in seabirds and contains predominantly methylmercury (MeHg). In this work, we developed a robust analytical technique for precise and accurate simultaneous quantification of MeHg, inorganic Hg (iHg) and consequently total Hg (THg), in feathers by gas-chromatography (GC)-ICPMS analyses using species-specific isotope dilution technique. An optimisation of the extraction method was carried out by testing different extraction systems, reagents and spiking procedures using an internal reference feather sample. The procedure was validated for MeHg and THg concentrations with a human hair certified reference material. Microwave nitric acid extraction with spike addition before the extraction provided the best recovery and was chosen as the most appropriate species simultaneous extraction method (SSE). An additional assessment was performed by comparison of our developed extraction method and a MeHg specific extraction technique (MSE) classically used for Hg speciation studies on feathers. The developed method was applied to feather samples from a large number of seabirds from the Southern Ocean (penguins, albatrosses, petrels and skuas) to investigate the variability of Hg speciation across a large range of Hg exposure conditions and concentrations. In all cases, MeHg accounted for > 90% of THg, thus verifying the predominance of organic Hg over iHg in feathers.

Pushing back the frontiers of mercury speciation using a combination of biomolecular and isotopic signatures: challenge and perspectives.

Mercury (Hg) pollution is considered a major environmental problem due to the extreme toxicity of Hg. However, Hg metabolic pathways in biota remain elusive. An understanding of these pathways is crucial to elucidating the (eco)toxic effects of Hg and its biogeochemical cycle. The development of a new analytical methodology based on both speciation and natural isotopic fractionation represents a promising approach for metabolic studies of Hg and other metal(loid)s. Speciation provides valuable information about the reactivity and potential toxicity of metabolites, while the use of natural isotopic signature analysis adds a complementary dynamic dimension that allows the life history of the target element to be probed, the source of the target element (i.e., the source of pollution) to be identified, and reactions to be tracked. The resulting combined (bio)molecular and isotopic signature affords precious insight into the behavior of Hg in biota and Hg detoxification mechanisms. In the long term, this highly innovative methodology could be used in life and environmental science studies of metal(loid)s to push back the frontiers of our knowledge in this field. This paper summarizes the current status of the application of Hg speciation and the isotopic signature of Hg at the biomolecular level in living organisms, and discusses potential future uses of this combination of techniques.

Specific Effects of Dietary Methylmercury and Inorganic Mercury in Zebrafish (Danio rerio) Determined by Genetic, Histological, and Metallothionein Responses.

A multidisciplinary approach is proposed here to compare toxicity mechanisms of methylmercury (MeHg) and inorganic mercury (iHg) in muscle, liver, and brain from zebrafish (Danio rerio). Animals were dietary exposed to (1) 50 ng Hg g(-1), 80% as MeHg; (2) diet enriched in MeHg 10000 ng Hg g(-1), 95% as MeHg; (3) diet enriched in iHg 10000 ng Hg g(-1), 99% as iHg, for two months. Hg species specific bioaccumulation pathways were highlighted, with a preferential bioaccumulation of MeHg in brain and iHg in liver. In the same way, differences in genetic pattern were observed for both Hg species, (an early genetic response (7 days) for both species in the three organs and a late genetic response (62 days) for iHg) and revealed a dissimilar metabolization of both Hg species. Among the 18 studied genes involved in key metabolic pathways of the cell, major genetic responses were observed in muscle. Electron microscopy revealed damage mainly because of MeHg in muscle and also in liver tissue. In brain, high MeHg and iHg concentrations induced metallothionein production. Finally, the importance of the fish origin in ecotoxicological studies, here the seventh descent of a zebrafish line, is discussed.

Specific Pathways of Dietary Methylmercury and Inorganic Mercury Determined by Mercury Speciation and Isotopic Composition in Zebrafish (Danio rerio).

An original approach is proposed to investigate inorganic (iHg) and methylmercury (MeHg) trophic transfer and fate in a model fish, Danio rerio, by combining natural isotopic fractionation and speciation. Animals were exposed to three different dietary conditions: (1) 50 ng Hg g(-1), 80% as MeHg; (2) diet enriched in MeHg 10,000 ng Hg g(-1), 95% as MeHg, and (3) diet enriched in iHg 10,000 ng Hg g(-1), 99% as iHg. Harvesting was carried out after 0, 7, 25, and 62 days. Time-dependent Hg species distribution and isotopic fractionation in fish organs (muscle, brain, liver) and feces, exhibited different patterns, as a consequence of their dissimilar metabolization. The rapid isotopic re-equilibration to the new MeHg-food source reflects its high bioaccumulation rate. Relevant aspects related to Hg excretion are also described. This study confirms Hg isotopic fractionation as a powerful tool to investigate biological processes, although its deconvolution and fully understanding is still a challenge.

Identical Hg isotope mass dependent fractionation signature during methylation by sulfate-reducing bacteria in sulfate and sulfate-free environment.

Inorganic mercury (iHg) methylation in aquatic environments is the first step leading to monomethylmercury (MMHg) bioaccumulation in food webs and might play a role in the Hg isotopic composition measured in sediments and organisms. Methylation by sulfate reducing bacteria (SRB) under sulfate-reducing conditions is probably one of the most important sources of MMHg in natural aquatic environments, but its influence on natural Hg isotopic composition remains to be ascertained. In this context, the methylating SRB Desulfovibrio dechloracetivorans (strain BerOc1) was incubated under sulfate reducing and fumarate respiration conditions (SR and FR, respectively) to determine Hg species specific (MMHg and IHg) isotopic composition associated with methylation and demethylation kinetics. Our results clearly establish Hg isotope mass-dependent fractionation (MDF) during biotic methylation (-1.20 to +0.58‰ for δ(202)Hg), but insignificant mass-independent fractionation (MIF) (-0.12 to +0.15‰ for Δ(201)Hg). During the 24h of the time-course experiments Hg isotopic composition in the produced MMHg becomes significantly lighter than the residual IHg after 1.5h and shows similar δ(202)Hg values under both FR and SR conditions at the end of the experiments. This suggests a unique pathway responsible for the MDF of Hg isotopes during methylation by this strain regardless the metabolism of the cells. After 9 h of experiment, significant simultaneous demethylation is occurring in the culture and demethylates preferentially the lighter Hg isotopes of MMHg. Therefore, depending on their methylation/demethylation capacities, SRB communities in natural sulfate reducing conditions likely have a significant and specific influence on the Hg isotope composition of MMHg (MDF) in sediments and aquatic organisms.

Transformation, localization, and biomolecular binding of Hg species at subcellular level in methylating and nonmethylating sulfate-reducing bacteria.

Microbial activity is recognized to play an important role on Hg methylation in aquatic ecosystems. However, the mechanism at the cellular level is still poorly understood. In this work subcellular partitioning and transformation of Hg species in two strains: Desulfovibrio sp. BerOc1 and Desulfovibrio desulfuricans G200 (which exhibit different Hg methylation potential) are studied as an approach to the elucidation of Hg methylation/demethylation processes. The incubation with isotopically labeled Hg species ((199)Hgi and Me(201)Hg) not only allows the determination of methylation and demethylation rates simultaneously, but also the comparison of the localization of the originally added and resulting species of such metabolic processes. A dissimilar Hg species distribution was observed. In general terms, monomethylmercury (MeHg) is preferentially localized in the extracellular fraction; meanwhile inorganic mercury (Hgi) is associated to the cells. The investigation of Hg binding biomolecules on the cytoplasmatic and extracellular fractions (size exclusion chromatography coupled to ICP-MS) revealed noticeable differences in the pattern corresponding to the Hg methylating and nonmethylating strains.

Novel approaches for selenium speciation in foodstuffs and biological specimens: a review.

Selenium is an essential element for human health. It has been recognized as an antioxidant and chemopreventive agent in cancer. Selenium is known to develop its biological activity via selenocysteine residue in the catalytically active centre of selenoproteins. The main source of selenium in human beings is the diet. However, in several regions of the world the content of selenium in diet has been estimated insufficient for a correct expression of the proteins. The beneficial effects of selenium on human health are strongly dependent on its chemical form and concentration. This review critically evaluated the state-of-the art of selenium speciation in biological matrices mainly focused in nutritional and food products. Besides the number of publications related to selenium speciation, isolation and accurate characterization and quantification of selenium species is still a challenge. Hyphenated techniques based on coupling chromatography separation with inductively coupled plasma spectrometry (ICP-MS) and its combination with molecular mass spectrometry (ESI-MS, ESI-MS-MS and MALDI-TOF) and isotopic dilution allow identification, quantification and structural characterization of selenium species. Particular attention is paid in the development of Se-enriched food and nutritional products and how the application of the techniques mentioned above is mandatory to get reliable results on selenium metabolisms in these particular matrices.

Protective effect of selenium in Broccoli (Brassica oleracea) plants subjected to cadmium exposure.

The protective effect of selenium against the cadmium-induced oxidative effect in broccoli ( Brassica oleracea) plants was studied. Plants grown in hydroponic culture were supplied with selenium [as Se(IV)] and cadmium [as Cd(II)], individually or simultaneously. Cadmium accumulation in roots was noticeably higher than in the aerial parts of the plants, and this effect was even more acute when selenium was simultaneously added. Cadmium phytotoxicity was evidenced by an increase in the malondialdehyde (MDA) concentration in the roots and a decrease of photosynthetic pigment and tocopherol concentration in the aerial parts of the plant. The simultaneous addition of selenium alleviated cadmium-induced stress in the roots after 40 days of exposition. In the leaves, a more remarkable decrease of tocopherol and chlorophyll concentration was observed in the cadmium-enriched plants after 10 days of exposure. The results provided evidence that selenium supplementation helps the plant to minimize the cadmium oxidant effect. Tocopherol concentration in broccoli fruit of cadmium-supplied plants was not affected in comparison to control. However, the proportion of alpha-tocopherol increases with the addition of selenium. This response is important not only for the protective effect against oxidative damage in the plant but also in terms of human nutrition.