The role of tropical small-scale fisheries in trace element delivery for a Small Island Developing State community, the Seychelles

Species-specific mercury speciation in billfishes and its implications for food safety monitoring and dietary advice

Humans are exposed to toxic methylmercury mainly by consuming marine fish, in particular top predator species like billfishes or tunas. In seafood risk assessments, mercury is assumed to be mostly present as organic methylmercury in predatory fishes; yet high percentages of inorganic mercury were recently reported in marlins, suggesting markedly different methylmercury metabolism across species. We quantified total mercury and methylmercury concentrations in muscle of four billfish species from the Indian and the Pacific oceans to address this knowledge gap. We found low percentages of methylmercury in blue and black marlins (15 ± 7 %) compared to swordfish and striped marlin (89 ± 13 %), with no significant differences among ocean regions. This illustrates that billfishes exhibit species-specific methylmercury bioaccumulation patterns, likely related to unique selenium-dependent in vivo methylmercury demethylation capacities in muscle. Blue and black marlins therefore appeared generally safer for human consumption than swordfish and striped marlin regarding MeHg toxicological effects. Yet, no matter the species, the frequency of recommended weekly billfish meals decreased with increasing fish size, given that mercury naturally accumulates over time. When assessing potential risks of billfish consumption, we therefore recommend measuring methylmercury, rather than total mercury, and relying on a large number of samples to cover a broad range of fish sizes. This study calls for additional characterization of mercury speciation and bioavailability in billfishes to better understand the mechanisms driving species-specific differences of methylmercury detoxification, and to refine dietary advices associated to marine top predators consumption.

Widespread presence of metallic compounds and organic contaminants across Pacific coral reef fish

Coral reef fishes represent an invaluable source of macro- and micro-nutrients for tropical coastal populations. However, several potentially toxic compounds may jeopardize their contribution to food security. Concentrations of metallic compounds and trace elements (MTEs), and persistent organic pollutants (POPs, including pesticides and polychlorobiphenyls PCBs), totalizing 36 contaminants, were measured in coral reef fish from several Pacific islands. The objective of this study was to describe the spatial distribution of these compounds and contaminants in order to identify potential variables explaining their distribution at a Pacific-wide scale. To achieve this, we applied Boosted Regression Trees to model species-specific and community-level contaminant and inorganic compound concentrations at the scale of the tropical Pacific Ocean. Overall, using 15 easily accessible explanatory variables, we successfully explained between 60 and 87 % of the global variation, with fish body size being the most important correlate of MTEs and POPs concentrations in reef fish. Our modeling approach allowed us to estimate and map the distribution of the community-level concentration of 19 contaminants and inorganic compounds at the scale of the equatorial and south Pacific Ocean. Spatial patterns varied significantly depending on the compound, with modeled quantities per 100 g of fish flesh generally being higher in the central and southwest Pacific than in the eastern part of the basin. These patterns were influenced by a combination of biological, environmental, anthropogenic and biogeographical variables. Overall, this approach represents an important step toward the estimation of concentrations of the main compounds on the basis of species identity and fishing location. Our results enhance our understanding of the extent of contamination in the Pacific while underscoring the urgent need for long-term and large-scale spatial monitoring of diverse compounds in this region.

Evaluation of Health Risks Attributed to Toxic Trace Elements and Selenium in Farmed Mediterranean Mussels from Türkiye and Bulgaria

Farmed mussels accumulate contaminants from their production environment rather than releasing them into water. This study reveals potential health risks associated with selenium, cadmium, mercury, and lead resulting from the consumption of mussels (Mytilus galloprovincialis) cultured along the coasts of Türkiye and Bulgaria. The concentrations of Se and toxic trace metals were measured by inductively coupled plasma mass spectrometry (ICP-MS). The detection limits (LOD) were 0.100, 0.015, 0.025, and 0.180 µg/kg for Se, Cd, Hg, and Pb, respectively. The mean Se concentrations were between 1.305 and 1.957 µg/g, and toxic metals were below the maximum limits. Due to Turkish and Bulgarian consumers' limited mollusk consumption, mussels could only provide a maximum of 7.35% of the daily Se need. THQ and TTHQ of Se, Cd, and methyl-Hg were below 1, indicating that farmed mussels were safe for consumption. Percent PTWI values were calculated only for Cd and MeHg, as the PTWI value for Pb was discarded by the authorities and not determined for Se. Accordingly, weekly mussel consumption did not pose any risks. The margin of exposure approach was used to evaluate Pb intake. MOE-SBP and MOE-NE were significantly higher than 10, designating no significant health risks. Long-term consumption of mussels also does not pose a carcinogenic risk regarding the TR index calculated between 10-5 and 10-6 for Pb. Positive HBVSe (10.13-37.27) indicated that Se in mussels overcame Hg-related potential health concerns. Consequently, mussels grown in Türkiye and Bulgaria did not pose a risk for human consumption, based on current risk analysis methods.

Persistent and Bioaccumulative Halogenated Natural Products in Various Tropical Reef Fish Species from the Seychelles, Western Indian Ocean

Gas chromatography with electron capture negative ion mass spectrometry (GC/ECNI-MS) was used to quantify and compare halogenated natural products (HNPs) and selected anthropogenic persistent organic pollutants (POPs) in individual samples of 17 fish species from the Seychelles (Western Indian Ocean). The sum-HNP amounts (9.5-1100 ng/g lipid mass (lm)) were between 1 and 2 orders of magnitude higher than those of the sum of seven abundant polychlorinated biphenyl (PCB) congeners (0.2-15 ng/g lm) and dichlorodiphenyltrichloroethane-related compounds (DDTs) (<1.1-43 ng/g lm). Within the group of HNPs, the two tetrabrominated phenoxyanisoles (aka methoxylated diphenyl ethers, MeO-BDEs), 2'-MeO-BDE 68 ≫ 6-MeO-BDE 47, were predominant in most cases. Pearson correlation analysis showed that MeO-BDE levels were positively correlated with less abundant HNPs (2,2'-diMeO-BB 80, 2',6-diMeO-BDE 68, and Br6-DBP) (p < 0.01). Accordingly, HNPs, rather than PCBs and DDTs, were the predominant polyhalogenated contaminants in the current species.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.

Dietary selenium and mercury intakes from fish consumption during pregnancy: Seychelles Child Development Study Nutrition Cohort 2

Some health agencies have issued precautionary principle fish advisories to pregnant women based on the presence of methylmercury (MeHg) in fish that could possibly be harmful to the developing fetus. Fish, however, is a rich source of selenium (Se) and other nutrients essential for normal brain development. Selenium is also thought to have a key role in alleviating MeHg toxicity. We estimated the dietary Se and MeHg intakes and dietary Se:Hg molar ratios from the fish consumed in a high fish-eating pregnant cohort where no adverse associations of fish consumption and outcomes has been reported. We used dietary data collected as part of the Seychelles Child Development Study Nutrition Cohort 2 (n = 1419). In this cohort 98% of participants consumed fish, with an average intake of 106.2 g per day. Daily Se intakes from fish consumption were 61.6 µg/ d, within the range recommended during pregnancy. The mean dietary Se:Hg molar ratios was 6. These findings demonstrate that fish consumption exposes pregnant Seychellois women to Se in excess of MeHg. Based on these findings, fish consumption, especially fish with Se:Hg ratios above 1, may help pregnant women achieve optimum dietary Se intakes, which may protect against MeHg toxicity.

Potential role of selenium in modifying the effect of maternal methylmercury exposure on child neurodevelopment - A review

Selenium (Se) is an essential trace element for normal neurodevelopment. It is incorporated into multiple selenoenzymes which have roles in the brain and neurological function, the synthesis of thyroid hormones, the antioxidant defense system, DNA synthesis, and reproduction. Fish is a source of both Se and neurotoxic methylmercury (MeHg). Selenium is known to ameliorate the effects of MeHg in experimental animals, but studies in children exposed to both Se and MeHg through prenatal fish consumption have been inconclusive. Research on Se's implications for pregnancy and child neurodevelopment is limited. The aims of this review are to summarize the literature on the biological roles of Se during pregnancy and the potential role in mitigating the effects of MeHg exposure from fish consumption on human health. This review has shown that Se concentrations among pregnant women globally appear insufficient, with the majority of pregnant women reporting Se concentrations below 70 µg/L during pregnancy. The role of Se in child development and its interactions with MeHg in children are inconclusive. Further investigation of the interaction between Se and MeHg in relation to child neurodevelopment in high fish-eating populations is required to fully elucidate effects.

Our evolved understanding of the human health risks of mercury

Mercury (Hg) is a chemical of health concern worldwide that is now being acted upon through the Minamata Convention. Operationalizing the Convention and tracking its effectiveness requires empathy of the diversity and variation of mercury exposure and risk in populations worldwide. As part of the health plenary for the 15th International Conference on Mercury as a Global Pollutant (ICMGP), this review paper details how scientific understandings have evolved over time, from tragic poisoning events in the mid-twentieth century to important epidemiological studies in the late-twentieth century in the Seychelles and Faroe Islands, the Arctic and Amazon. Entering the twenty-first century, studies on diverse source-exposure scenarios (e.g., ASGM, amalgams, contaminated sites, cosmetics, electronic waste) from across global regions have expanded understandings and exemplified the need to consider socio-environmental variables and local contexts when conducting health studies. We conclude with perspectives on next steps for mercury health research in the post-Minamata Convention era.

Marine Capture Fisheries from Western Indian Ocean: An Excellent Source of Proteins and Essential Amino Acids

The Republic of Seychelles is located in Western-Central Indian Ocean, and marine capture fisheries play a key role in the country's economic and social life in terms of food security, employment, and cultural identity. The Seychellois are among the highest per capita fish-consuming people in the world, with a high reliance on fish for protein. However, the diet is in transition, moving towards a Western-style diet lower in fish and higher in animal meat and easily available, highly processed foods. The aim of this study was to examine and evaluate the protein content and quality of a wide range of marine species exploited by the Seychelles industrial and artisanal fisheries, as well as to further to assess the contribution of these species to the daily intake recommended by the World Health Organization (WHO). A total of 230 individuals from 33 marine species, including 3 crustaceans, 1 shark, and 29 teleost fish, were collected from the Seychelles waters during 2014-2016. All analyzed species had a high content of high-quality protein, with all indispensable amino acids above the reference value pattern for adults and children. As seafood comprises almost 50% of the consumed animal protein in the Seychelles, it is of particular importance as a source of essential amino acids and associated nutrients, and as such every effort to sustain the consumption of regional seafood should be encouraged.