Selenium-Mercury Balance in Commercial Fish Species from the Turkish Waters

Exploring mercury detoxification in fish: The role of selenium from tuna byproduct diets for sustainable aquaculture

Exposure to mercury (Hg) through fish consumption poses significant environmental and public health risks, given its status as one of the top ten hazardous chemicals. Aquaculture is expanding, driving a surge in demand for sustainable aquafeeds. Tuna byproducts, which are rich in protein, offer potential for aquafeed production, yet their use is challenged by the high content of heavy metals, particularly Hg. However, these byproducts also contain elevated levels of selenium (Se), which may counteract Hg adverse effects. This study examines the fate of dietary Hg and Se in an aquaculture model fish. Biomolecular speciation analyses through hyphenated analytical approaches were conducted on the water-soluble protein fraction of key organs of juvenile rainbow trout (Oncorhynchus mykiss) exposed to various combinations of Hg and Se species, including diets containing tuna byproducts, over a six-month period. The findings shed light on the dynamics of Hg and Se compounds in fish revealing potential Hg detoxification mechanisms through complexation with Hg-biomolecules, such as cysteine, glutathione, and metallothionein. Furthermore, the trophic transfer of selenoneine is demonstrated, revealing novel opportunities for sustainable aquafeed production. Understanding the interactions between Hg and Se in aquaculture systems is crucial for optimizing feed formulations and mitigating environmental risks. This research contributes to the broader goal of advancing sustainable practices in aquaculture while addressing food security challenges.

Se and Hg in processed fish-derived products and their fish raw materials: Occurrence, Se:Hg molar ratio, HBVSe index, bioaccessibility and Caco-2 cells toxicity

Processing conditions applied during food production could affect food component contents and bioaccessibility. Here, possible changes in Hg and Se total and species contents and bioaccessibility have been tracked in each stage of the production chain of processed fish-derived products. Therefore, Se:Hg molar ratio and Selenium Health Benefit Value (HBVSe) were calculated for final products and raw materials, resulting favorable in all cases, suggesting the safety of surimi-based products regarding mercury. Speciation studies revealed the presence of SeMeSeCys and SeMet in all samples. Thus, the integrity of the selenium species seems to be maintained. Moreover, in vitro gastrointestinal digestion model evidenced that Se bioaccessibility ranged between 20-39 % for all samples, while in case of Hg was between 8-37 %. Additionaly, SeMeSeCys and SeMet were also identified in the gastrointestinal extracts. Finally, no cytotoxicity was observed after exposure of Caco-2 cells to the gastrointestinal extracts.

P. Oliveira MB, Prieto MA. Health benefits of bluefin tuna consumption: (Thunnus thynnus) as a case study

Consumers are increasingly interested in food products with high nutritional value and health benefits. For instance, fish consumption is linked with diverse positive health benefits and the prevention of certain widespread disorders, such as obesity, metabolic syndrome, or cardiovascular diseases. These benefits have been attributed to its excellent nutritional value (large amounts of high-quality fatty acids, proteins, vitamins, and minerals) and bioactive compounds, while being relatively low-caloric. Atlantic bluefin tuna (Thunnus tynnus) is one of the most consumed species worldwide, motivated by its good nutritional and organoleptic characteristics. Recently, some organizations have proposed limitations on its consumption due to the presence of contaminants, mainly heavy metals such as mercury. However, several studies have reported that most specimens hold lower levels of contaminants than the established limits and that their richness in selenium effectively limits the contaminants' bioaccessibility in the human body. Considering this situation, this study aims to provide baseline data about the nutritional composition and the latest evidence regarding the beneficial effects of Atlantic bluefin tuna consumption. A review of the risk-benefit ratio was also conducted to evaluate the safety of its consumption, considering the current suggested limitations to this species' consumption.

Monthly variation of fatty acids, lipid quality index and metal content of Pontastacus leptodactylus (Eschscholtz, 1823) in Atikhisar Dam Lake (Çanakkale, Türkiye)

This study aims to investigate the metal content, fatty acid composition, lipid quality, and potential health risks of Pontastacus leptodactylus crayfish inhabiting Atikhisar Dam Lake. The research covers a 12-month period and includes both male and female individuals. The study investigated the metal content of crayfish specimens. In female individuals, the metal concentrations were ranked as Fe > Zn > Al > Cu > Mn > Se > As > Hg > Cd > Pb, while in male individuals, the ranking was Fe > Al > Zn > Cu > Mn > Se > As > Hg > Pb > Cd. The results demonstrate that Atherogenicity Index (AI) values for both genders range between 0.21 and 0.31, and Thrombogenicity Index (TI) values fall within 0.14 and 0.20. This indicates that crayfish meat is composed of healthy and high-quality fatty acids. In male individuals, omega-3 values range from 25.28 ± 0.380% to 28.34 ± 0.430%, and in female individuals, they vary from 22.98 ± 0.195% to 28.73 ± 0.871%. These findings underscore the absence of significant health risks associated with mercury levels in crayfish meat. Monthly meal calculations reveal that consuming female crayfish at an average of 4.35 servings per month for adults and 2.24 servings per month for children presents no health hazards. Similarly, the consumption of crayfish meat at an average of 5.29 servings per month for adult males and 2.72 servings per month for male children is deemed safe for health. Based on these results, the lipid quality of both male and female individuals from this species is found to be beneficial, as confirmed by risk-benefit assessments.

Selenium Health Benefit Values and Hg and Se speciation studies for elucidating the quality and safety of highly consumed fish species and fish-derived products

Nowadays, there has been an increase in the consumption of fish-derived products that constitute alternative ways of introducing fish into the diet, such as fish roe and products made from fish (crab sticks andsurimi-derived products). However, there is no data available considering selenium and mercury total contents along with speciation studies in these kinds of samples, which are mandatory for a proper safety and quality assessment. In this study,Selenium Health Benefit Values (HBVSe) in fish and fish-derived products were evaluated, resulting inpositivein all cases. Selenium speciation studies performed by HPLC-ICP-MS and confirmed by HPLC-ESI-MS/MS revealed that SeMet and SeMeSeCys are present in fish and fish-derived products. Finally, Hg speciation studiesshow that the percentage of Hg2+ increases in fishes lower in the food chain as well as in fish-derived products.

Selenium in the liver facilitates the biodilution of mercury in the muscle of Planiliza haematocheilus in the Jiaozhou Bay, China

There are increasing evidences that the biodilution effect can significantly reduce the biomagnification of mercury (Hg) in fish. The significant antagonism of selenium (Se) -Hg may have a potential diluting effect on Hg in fish; however, there is still lack of knowledge on such effect. To reveal the Se-Hg interaction and its role in controlling the biodilution effect of Hg, we investigated levels of Hg and Se in the muscle and liver of redlip mullet from Jiaozhou Bay, China, an urbanized semi-enclosed bay highly impacted by human activities. In general, Hg levels in fish muscle were significantly negatively correlated to the levels of Se in the liver and fish size for fish with a size of < 200 mm, indicating that the antagonistic effect of Se on Hg increased with fish growth. This relationship was not significant for fish with a size of > 200 mm, possibly because the normal metabolism of Hg in muscle was hindered by homeostatic regulation or physiological activities such as gonadal development in vivo. Furthermore, the molar ratio of Se in the liver/Hg in the muscle was significantly increasing with Se/Hg in the liver, suggesting that the liver may be the key organ involved in Se-Hg antagonism. Moreover, both ratios continued to decrease with increasing fish size, implying that the antagonistic effect weakens with fish growth. These results indicate that Hg sequestration by liver may be a key mechanism of Se-Hg antagonism in fish and function as a driver for the biodilution effect of Hg, especially at a size of < 200 mm. These findings are further supported by the established linear model of Se-Hg antagonism at different developmental stages.

Metal concentrations, selenium-mercury balance, and potential health risk assessment for consumer of whiting (Merlangius merlangus euxinus L., 1758) from different regions of the southern Black Sea

The significant increase in the human population and the associated industrial wastes have a widespread impact on coastal areas. It is important to monitor trace elements that affect food safety and pose a potential consumer health threat. All over the Black Sea coast, people enjoy consuming whiting as both meat and roe. In February 2021, whitings were caught by bottom trawling from four different locations on the coasts of Kastamonu, Sinop (Sarıkum, Adabaşı), and Samsun in the southern Black Sea region. The meat and roe extracts obtained from whiting samples were analyzed through an optical emission spectrophotometer (ICP-MS). Trace element concentrations of whiting meat and roe in this study were Zn > Fe > Sr > As > Al > Se > B > Mn > Cu > Hg > Li > Ni > Ba > Pb > Cr > Cd and Zn > Fe > Al > As > Cu > Sr > Mn > Se > B > Ba > Li > Ni > Hg > Cr > Pb > Cd, respectively. These amounts were lower than the acceptable values accepted by the EU Commission. In case of whiting and roe consumption of a maximum of three portions (860.33 g) for Adabaşı, six portions for Kastamonu (1432.37 g), three portions for Samsun (828.55 g), and five portions (1253.04 g) for Sarıkum per month do not pose a health risk.

Element concentrations of cultured fish in the Black Sea: selenium-mercury balance and the risk assessments for consumer health

Fish are a powerful model for risk-benefit analyses to explore the impact of elements on human health among all accessible species. The sea bream (Sparus aurata), sea bass (Dicentrarchus labrax), turbot (Scophthalmus maximus), and weights of > 1 kg large rainbow trout registered as "Turkish Salmon," (Oncorhynchus mykiss) are four economically important cultured species in the Black Sea In this research, it is aimed (1) to determine the value of the elements, (2) to determine total Hg and Se concentrations, Se/Hg molar ratios, and the HBVSe index, and (3) to calculate the consumer's possible health risk in the edible tissues of cultivated four economically important Black Sea fish species. Fish and diet samples from all species were obtained in 2020 from aquaculture locations in the Black Sea (Sinop, Samsun, and Trabzon cites of Turkey). At the end of the study, the elements in all edible tissues and all the parameters analyzed [Se/Hg, estimated daily intake (EDI), target hazard quotient (THQ), maximum allowable consumption rate (CR_lim and CR_mm)] in cultured fish tissues were below permissible values. Additionally, when compared with the data of the World Health Organization and The National Academy of Sciences, it determined that consuming cultured fish in the Black Sea adequately meets the daily elemental requirement.

Trace elements in seabass, farmed by Turkey, and health risks to the main consumers: Turkish and Dutch populations

Turkey ranked first in sea bass farming in Europe, and almost all extra-EU seabass come from this country. The share of Turkish sea bass in the fish consumption of Europeans has increased significantly, and assessment of potential health risks of trace metals via sea bass, cultured by Turkey, became important. The Netherlands is the main buyer of the Turkish sea bass. Therefore, potential health risks were determined for Turkish and Dutch consumers. In the study, the concentrations of lead (Pb) and mercury (Hg) were below the limits, but the level of cadmium (Cd) was above the guidelines, in spring and winter. Dietary intake and potential health risk were found higher for the Dutch consumer, but all target hazard quotients (THQs) and total THQ (TTHQ) values were well below 1, showing no significant health risk due to the consumption of sea bass, cultured and exported by Turkey. It was determined that these sea basses can be safely consumed in quite high amounts, such as at least 31 meals a month. Se/Hg molar ratios were all above 1 and selenium health benefit values (Se-HBVs) were positive, indicating that selenium (Se) had a protective effect on Hg toxicity and positive health effects. Considering the average annual intake in Turkey and Netherlands, the consumption of sea bass, cultured by Turkey, is safe. Since the risk levels of communities may differ due to their eating habits, it is important to determine the public health impacts of the international fish trade.

Determination of Mercury, Methylmercury and Selenium Concentrations in Elasmobranch Meat: Fish Consumption Safety

This study measures total mercury (THg), methylmercury (MeHg) and selenium (Se) concentrations in elasmobranch fish from an Italian market with the aim of evaluating the risk-benefit associated with their consumption, using estimated weekly intake (EWI), permissible safety level (MeHg_PSL), selenium health benefit value (HBV_Se) and monthly consumption rate limit (CR_mm) for each species. THg and Se were analysed by atomic absorption spectrometry, while MeHg was determined by HrGc/Ms. THg and MeHg concentrations ranged from 0.61 to 1.25 μg g^-1 w.w. and from 0.57 to 0.97 μg g^-1 w.w., respectively, whereas Se levels were 0.49-0.65 μg g^-1 w.w. In most samples European Community limits for THg were surpassed, while for MeHg none of the fish had levels above the limit adopted by FAO/WHO. EWIs for THg and MeHg in many cases were above the provisional tolerable weekly intakes (PTWIs). MeHg_PSL estimate showed that fish should contain approximately 50% of the concentration measured to avoid exceeding the PTWI. Nevertheless, the HBV_Se index indicated that solely skates were safe for human consumption (HBV_Se = 3.57-6.22). Our results highlight the importance of a constant monitoring of THg and MeHg level in fish, especially in apex predators, to avoid the risk of overexposure for consumers.

Connecting inorganic mercury and lead measurements in blood to dietary sources of exposure that may impact child development

Pre-natal and post-natal chemical exposures and co-exposures from a variety of sources including contaminated air, water, soil, and food are common and associated with poorer birth and child health outcomes. Poor diet is a contributing factor in the development of child behavioral disorders. Child behavior and learning can be adversely impacted when gene expression is altered by dietary transcription factors such as zinc insufficiency or deficiency or by exposure to toxic substances permitted in our food supply such as mercury, lead, or organophosphate pesticide residue. Children with autism spectrum disorder and attention deficit hyperactivity disorders exhibit decreased or impaired PON1 gene activity which is needed by the body to metabolize and excrete neurotoxic organophosphate pesticides. In this current review we present an updated macroepigenetic model that explains how dietary inorganic mercury and lead exposures from unhealthy diet may lead to elevated blood mercury and/or lead levels and the development of symptoms associated with the autism and attention deficit-hyperactivity disorders. PON1 gene activity may be suppressed by inadequate dietary calcium, selenium, and fatty acid intake or exposures to lead or mercury. The model may assist clinicians in diagnosing and treating the symptoms associated with these childhood neurodevelopmental disorders. Recommendations for future research are provided based on the updated model and review of recently published literature.

Selenium and mercury balance in sea bream obtained from different living environments in Turkey: a risk assessment for the consumer health

The selenium health benefit value (Se-HBV) is the criterion developed for revealing nutritional values or the risks related to mercury (Hg) toxicity which can emerge in relation to consumption of fish. In this study, the conditions of Se and Hg elements in the muscular tissues of sea bream (Sparus aurata) living in different environments in Mugla province were examined. In addition, a benefit/risk assessment was performed in terms of consumer health with the calculation of Se-HBV. In this context, muscular tissues of sea bream obtained from wild species (WS), offshore marine cages species (OS), and soil ponds species (SS) were dissolved with microwave wet digestion and the concentrations of Se and Hg (mg/kg wet weight) were determined by using inductively coupled plasma mass spectroscopy (ICP-MS). According to the obtained results, the highest mean Se level was determined in SS (0.43 ± 0.02 mg/kg) followed by WS (0.35 ± 0.03 mg/kg) and OS (0.34 ± 0.02 mg/kg). The highest mean Hg concentration was detected in WS (0.09 ± 0.02 mg/kg) followed by OS and SS as 0.05 ± 0.01 mg/kg respectively. As a result of risk assessment conducted with Se-HBV, positive values were determined for each one of three sea bream groups.

Biomonitoring selenium, mercury, and selenium:mercury molar ratios in selected species in Northeastern US estuaries: risk to biota and humans

The mutual mitigation of selenium and mercury toxicity is particularly interesting, especially for humans. Mercury is widely recognized as a pantoxic element; all forms are toxic to all organisms. Less well known is that selenium in excess is toxic as well. The high affinity between these elements influences their bioavailability and toxicity. In this paper, we use selected species from Barnegat and Delaware Bays in New Jersey to examine variations in levels of selenium and mercury, and selenium:mercury molar ratios between and within species. We report on species ranging from horseshoe crab eggs (Limulus polyphemus), a keystone species of the food chain, to several fish species, to fish-eating birds. Sampling began in the 1970s for some species and in the 1990s for others. We found no clear time trends in mercury levels in horseshoe crab eggs, but selenium levels declined at first, then remained steady after the mid1990s. Concentrations of mercury and selenium in blood of migrant shorebirds directly reflected levels in horseshoe crab eggs (their food at stopover). Levels of mercury in eggs of common terns (Sterna hirundo) varied over time, and may have declined slightly since the mid2000s; selenium levels also varied temporally, and declined somewhat. There were variations in mercury and selenium levels in commercial, recreational, and subsistence fish as a function of species, season, and size (a surrogate for age). Selenium:mercury molar ratios also varied as a function of species, year, season, and size in fish. While mercury levels increased with size within individual fish species, selenium levels remained the same or declined. Thus selenium:mercury molar ratios declined with size in fish, reducing the potential of selenium to ameliorate mercury toxicity in consumers. Mercury levels in fish examined were higher in early summer and late fall, and lower in the summer, while selenium stayed relatively similar; thus selenium:mercury molar ratios were lower in early summer and late fall than in midsummer. We discuss the importance of temporal trends in biomonitoring projects, variations in levels of mercury, selenium, and the molar ratios as a function of several variables, and the influence of these on risks to predators and humans eating the fish, and the eggs of gulls, terns. Our data suggests that variability limits the utility of the selenium:mercury molar ratio for fish consumption advisories and for risk management.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

Determination of heavy metals in selected fish species and seawater from the South Durban Industrial Basin, KwaZulu-Natal, South Africa

The South Durban Industrial Basin (SDIB), South Africa, an economic hub that spans a long coastline, is a disaster management hotspot, which threatens the sustainability of the fishing industry in this region. This study investigated the elemental concentrations in fish and seawater from a mini-ecosystem in the SDIB, to determine if a direct relationship exists between these two matrices, and to assess for metal toxicities. The results showed As and Cr to be above the maximum permissible limits (MPLs) of the World Health Organization (WHO) for all fish species (blacktail, karanteen, five finger, mullet, and pompano), while fish from Isipingo Beach exceeded the WHO MPLs for Pb, As, and Cr. Fish did not display signs of metal toxicity indicating either a harmless form of metals or high tolerance levels. Typical concentrations of metals in seawater (mg L^-1) at (Isipingo Beach, Cuttings Beach, and Amanzimtoti Beach) were found to be for Al (3, 2.7, and 16.4), As (0.17, 0.11, and 0.19), Cr (0.16, 0.17, and 0.23), Cu (0.15, 0.13, and 0.24), Fe (2.7, 3.45, and 33.9), and Zn (2, 2.1, and 2.12). Except for As, estimated daily intakes, target hazard quotients, and carcinogenic risks indicated no associated health risks due to consumption of the fish from the SDIB. However, due to target hazard quotients and carcinogenic risks for As being above 4 and 0.0001, respectively, fish from the SDIB should be consumed in moderation or not consumed to prevent long-term toxic effects of As.

Levels of Mercury, Methylmercury and Selenium in Fish: Insights into Children Food Safety

Total mercury (THg), methylmercury (MeHg), and selenium (Se) concentrations were measured in various commercially important fish species. The benefit-risk binomial associated with these chemicals was assessed in children through the probability of exceeding the provisional tolerable weekly intakes (PTWIs) of the contaminants and the Se recommended dietary allowance (RDA). The Se:Hg molar ratios, selenium health benefit values (HBVSe), and monthly consumption rate limits (CRmm) for each species were also calculated. THg and Se were analyzed by atomic absorption spectrophotometer (Shimadzu, Milan, Italy), while MeHg was determined by Trace Ultra gas chromatograph connected with a PolarisQ MS (Thermo Fisher Scientific, Waltham, MA, USA). None of the analyzed fish had Hg levels above the European Community regulatory limits, while most large predators had MeHg levels over the threshold concentration set by US EPA. The estimated weekly intakes of THg and MeHg exceeded in many cases the PTWIs and the Se estimated daily intakes were provided from 0.71% to 2.75% of the RDA. Se:Hg molar ratios above 1 and positive HBVSe index suggested that Se in fish could be enough to alleviate the potential toxic effect of Hg. However, high-risk groups as children should consume fish in moderation because a large consumption pattern, especially of swordfish and tunas, might be of concern for health.

Comparison of Zinc, Copper and Selenium Content in Raw, Smoked and Pickled Freshwater Fish

The aim of the study was to assess the zinc (Zn), copper (Cu) and selenium (Se) content in freshwater fish from Poland. Selected species of raw, smoked and pickled fish were evaluated by atomic absorption spectrometry (AAS). The concentration of Zn, Cu and Se in the examined fish ranged from 1.5 to 49.9 mg/kg, 0.01 to 2.8 mg/kg and 30.9 to 728.2 µg/kg, respectively. One serving of every fish product covered the recommended dietary allowance (RDA) of Zn by 5.38-65.0%, of Cu by 0.42-11.4% and of Se by 12.3-198.6%. A cluster analysis allowed us to distinguish European eel (raw and smoked) based on the Zn content. Additionally, based on the Cu and Se content, pickled common whitefish was differentiated from other species and types of fish products. The discriminant analysis model of smoked fish enabled their classification with a 70% accuracy. Regarding Zn, all forms of the European eel as well as raw and smoked vendace can be considered a source of this element. None of the tested fish can be considered a source of Cu. All products are safe for human consumption with regard to the Zn and Cu content. Almost each form of every species of fish can be considered a source of Se. However, the Se content should be monitored in smoked and pickled common whitefish, pickled bream and pickled vendace.

Health risk assessment: heavy metals in fish from the southern Black Sea

Introduction. The coastal contamination of the Black Sea has been an important issue for several decades. Heavy metals are the most harmful contaminants which affect people health. The research objective of the present study was to determine the amounts of Cd, Hg, Pb, Cu, and Zn found in the whiting (M. merlangus L.) and the red mullet (M. barbatus L.). These Black Sea bottom fish species have the highest commercial value. The obtained data were used to assess the risk which the fish represents for human consumers. Study objects and methods. The elements were detected using an inductively coupled plasma mass spectrometer (ICP-MS). The amounts of the metals arranged in the following order: Zn > Cu > Pb > Hg > Cd. Results and discussion. The mean values of Cd, Hg, Pb, Cu, and Zn in the edible tissues were 0.013, 0.024, 0.07, 0.195, and 9.05 mg/kg wet wt. for whiting and 0.017, 0.036, 0.05, 0.29, and 6.4 mg/kg wet wt. for red mullet, respectively. These levels proved lower than the permitted values set by the Ministry of Agriculture, Forestry, and Fisheries of the UK (MAFF), Turkish Food Codex (TFC), and EU Commission Regulation. The target hazard quotient (THQ) for all the elements via consumption of whiting and red mullet were also low. Conclusion. Hazard index (HI) was ˂ 1, which means that the fish caused no health problems in people who consumed whiting and red mullet caught in the southern Black Sea during the fishing seasons of 2017–2018. The carcinogenic risk index (CRI) for whiting and red mullet was also considered insignificant.