Factors affecting mercury concentrations in two oceanic cephalopods of commercial interest from the southern Caribbean

Mercury (Hg) concentrations have significantly increased in oceans during the last century. This element accumulates in marine fauna and can reach toxic levels. Seafood consumption is the main pathway of methylmercury (MeHg) toxicity in humans. Here, we analyzed total Hg (T-Hg) concentrations in two oceanic squid species (Ommastrephes bartramii and Thysanoteuthis rhombus) of an increasing commercial interest off Martinique, French West Indies. Stable isotope ratios reveal a negative linear relationship between δ¹⁵N or δ¹³C in diamondback squid samples. No significant trend was observed between δ³⁴S values and T-Hg concentrations, contrasting with the sulfate availability and sulfide abundance hypotheses. This adds to a growing body of evidence suggesting Hg methylation via sulfate-reducing bacteria is not the main mechanism driving Hg bioavailability in mesopelagic organisms. All squid samples present T-Hg levels below the maximum safe consumption limit (0.5 ppm), deeming the establishment of a commercial squid fishery in the region safe for human consumption.

Mercury in neonatal and juvenile blacktip sharks (Carcharhinus limbatus). Part I: exposure assessment

Elasmobranchs are exposed to mercury (Hg) through a variety of pathways in the environment. This study assessed maternal offloading and diet-based Hg exposure for neonatal and juvenile blacktip sharks (Carcharhinus limbatus) from Charlotte Harbor located along southwest Florida's coast, a recognized Hg hotspot. Neonates (n = 57) had highest total Hg (THg) concentrations in the kidney (0.56 ± 0.26 mg kg^-1; n = 38) and muscle (0.53 ± 0.17 mg kg^-1; n = 57), followed by liver (0.31 ± 0.11 mg kg^-1; n = 38), and blood (0.05 ± 0.033 mg kg^-1; n = 57). Juveniles (n = 13) exhibited a different distribution with highest THg in the liver (0.868 ± 0.54 mg kg^-1; n = 6), followed by the muscle (0.84 ± 0.28 mg kg^-1; n = 13), kidney (0.55 ± 0.22 mg kg^-1; n = 6), and blood (0.11 ± 0.04 mg kg^-1; n = 11). The distribution of THg among tissues and liver-to-muscle ratios indicated that Hg originated primarily from maternal offloading in neonates, whereas juveniles continued to accumulate Hg through dietary exposure post-parturition. Additionally, comparisons between results of the present study and previous Florida blacktip shark surveys suggested that Hg levels have not declined in southwest Florida estuaries for over two decades.

Total mercury in commercial fishes and estimation of Brazilian dietary exposure to methylmercury

BACKGROUND

Mercury, in particular its most toxic form methylmercury, poses a risk to public health. Dietary methylmercury exposure is mainly by fish, and it can vary with fish contamination and by dietary habits of the population. This study aimed to quantify total mercury levels in different fish from Brazil and to estimate Brazilian exposure to methylmercury by fish consumption.

METHODS

Total mercury occurrence was investigated in 18 different fish species by atomic absorption spectrometry with thermal decomposition and gold amalgamation. Dietary exposure to methylmercury was estimated by a deterministic method for different groups considering consumption by sex, different Brazilian geographical regions and habitat (rural or urban).

RESULTS

Carnivorous fish showed higher levels of mercury (0.01 to 0.93 mg/kg) compared to non-strictly carnivorous fish (<0.01 to 0.30 mg/kg). Farmed fishes showed significantly lower levels compared to wild fish. Mean Brazilian fish consumption achieves FAO/WHO health recommendation of about two portions of fish per week. However, there is a large difference between fish consumption at urban and rural homes and among Brazilian geographic regions. These differences in consumption impacted estimated methylmercury intake that was higher in the Northern (1.85 μg/kg bw week) and in the Northeastern (0.72 μg/kg bw week) regions and also by rural population (1.08 μg/kg bw week). These values were compared with the toxicological reference dose for neurotoxicity of 1.6 μg/kg bw week.

CONCLUSION

Even though total levels of mercury in fish were lower than Brazilian and international legislations, in the Northern Brazilian region methylmercury intake overpassed the toxicological reference dose for neurotoxicity and in rural areas it achieved 68% of this reference dose.

Evaluating the concentrations of total mercury, methylmercury, selenium, and selenium:mercury molar ratios in traditional foods of the Bigstone Cree in Alberta, Canada

Traditional foods provide nutritional, social, and economic benefits for Indigenous communities; however, anthropogenic activities have raised concerns about mercury (Hg), especially methylmercury (MeHg), in these foods. This issue may be of particular concern for communities near large industrial activities, including the Bigstone Cree Nation adjacent to the Athabasca oil sands region, Canada. This community-led study sought to assess variation in THg and MeHg concentrations among traditional food types (plants or animals), species, and tissues (muscles, organs), and variation in concentrations of the micronutrient selenium (Se)- thought to protect against Hg toxicity-and Se:THg ratios. Thirteen plant and animal species were collected in 2015 by Bigstone Cree community members. We quantified THg, Se, and Se:THg ratios in 65 plant and 111 animal samples and MeHg in 106 animal samples. For plants, the lichen, old man's beard (Usnea spp.), showed the highest concentrations of THg and Se (0.11 ± 0.02 and 0.08 ± 0.01 μg g^-1 w. w., respectively) and also had a low Se:THg molar ratio. Concentrations of THg, MeHg, and Se differed among animal samples (P < 0.010), showing variation among species and among tissues/organs. Generally, concentrations of THg and MeHg were highest in aquatic animals, which also had relatively low Se:THg molar ratios. Overall results revealed substantial variation in the patterns of THg, MeHg, Se and Se:THg ratios across this comprehensive basket of traditional foods. Thus, measuring concentrations of THg alone, without considering MeHg and potential associations with Se, may not adequately convey the exposure to Hg in traditional foods.

Total Mercury Levels in Commercial Fish in Market of the Republic of Srpska, Bosnia and Herzegovina

The mercury concentration was quantified in frozen and canned fish found in the market of the Republic of Srpska, Bosnia and Herzegovina. Using the method of amalgamation by atomic absorption spectrophotometry with a direct mercury analyzer (DMA-80), significant differences in mercury concentrations among the analyzed fish were found. Frozen pangasius and canned tuna had the highest mercury concentration (59.1 μg/kg and 54.1 μg/kg, respectively). Also, fish from Vietnam had the highest level of total mercury in comparison to fish from other countries. Determined levels of mercury in our samples were below the limit set by the European and Bosnian and Herzegovinian legislation (500 μg/kg wet weight). We have concluded that consumption of commercial fish in the market of the Republic of Srpska does not present any health risk for the average consumer. Nevertheless, a surveillance system of mercury content in fishery products, especially in certain species that concentrate mercury, is crucial for public health protection.

Toxicity and Organ Distribution of Mercury in Freshwater Fish (Oreochromis niloticus) after Exposure to Water Contaminated Mercury (HgII)

The purpose of this study was to investigate the toxicity and the distribution of mercury (Hg) in the main tissues of freshwater fish (Oreochromis niloticus) after being exposed to water containing Hg(II). A sample group of 10 fish, of mean weight 80–100 g wet weight, were exposed to different concentrations of Hg (0.0012; 0.0049; 0.0141; 0.0524; 0.1126; and 0.5110 mg-HgII/L) for 72 h under controlled conditions using the static method in ponds. A control medium was also prepared in two replications. Mortality of fish was closely monitored, and the test was repeated three times. For the toxicity test, observations were based on behavior, mortality, and anatomical pathology. The methodology was based on the OECD guidelines for testing of chemicals and lethal concentration (LC₅₀) and particularly using the probit method. Thus, the mean value was obtained from two replications and then further calculated by a software (MiniTab® 16 version). Prior to analysis, samples were first lyophilized. The total concentration of Hg accumulation in the fish organs was analyzed using heat-vaporization atomic absorption spectrometry (HV-AAS) and a MA2000 automatic mercury analyzer. Results showed that toxicity (LC₅₀) of freshwater fish was 0.1435 mg-Hg(II)/L. The internal organs showed some pathological changes including pale gills, anemic eyes, and a whitish body color after the exposure. Furthermore, histopathologically, exposure to mercury might also affect other organs, such as gills, liver, and hepatopancreas. Mercury was found in trace amounts, and its accumulation was found to be at least in the gills. Meanwhile, the highest accumulation was found in the muscle tissue with approximately 5.7183 µg/g dry weight. If they are put in order, the mercury accumulation in the tissue organs was varied from the highest to lowest one: Muscle > eye > bone > head > gill. Finally, it can be concluded that the Hg exposure could affect the histopathological condition of the tested fish.

Mercury in aquatic fauna contamination: A systematic review on its dynamics and potential health risks

Mercury is an important pollutant, released into aquatic ecosystems both naturally and by anthropogenic action. This element is transferred to aquatic organisms in different ways, causing potential health risks. In addition, mercury can be accumulated by humans, especially through the consumption of contaminated food. This systematic review aims to present mercury pathways, the major routes through which this element reaches the aquatic environment and its transformations until becoming available to living animals, leading to bioaccumulation and biomagnification phenomena. The key biotic and abiotic factors affecting such processes, the impact of mercury on animal and human health and the issue of seafood consumption as a source of chronic mercury contamination are also addressed. A total of 101 articles were retrieved from a standardized search on three databases (PubMed, Emabse, and Web of Science), in addition to 28 other studies not found on these databases but considered fundamental to this review (totaling 129 articles). Both biotic and abiotic factors display fundamental importance in mediating mercurial dynamics, i.e., muscle tropism, and salinity, respectively. Consequently, mercurial contamination in aquatic environments affects animal health, especially the risk of extinction species and also on human health, with methylmercury the main mercury species responsible for acute and chronic symptomatology.

Assessment of sampling methods about level of mercury in fish

Mercury (Hg) seriously affects some sensitive subgroups of population and the detection of Hg content in fish and fishery products is one of the most important activities aimed at controlling their safety. In fact, Regulation (EC) No 1881/2006 set maximum levels for certain contaminants in foodstuffs and Regulation (EC) No 333/2007 laid down the methods of sampling and analysis for their control in foodstuffs. As Hg content highly varies among different fish species depending on a variety of factors and even among members of the same population, sampling methods play a crucial role in the accuracy, precision and statistical significance of Hg determination. By the use of an analysis method independent probabilistic model, based on the axioms of Kolmogorov's probability theory, this paper aims to assess the relationship between sampling methods set by Regulation (EC) No 333/2007 and the probability to detect compliant or non-compliant outcomes of Hg in fish.

A multidimensional concept for mercury neuronal and sensory toxicity in fish - From toxicokinetics and biochemistry to morphometry and behavior

BACKGROUND

Neuronal and sensory toxicity of mercury (Hg) compounds has been largely investigated in humans/mammals with a focus on public health, while research in fish is less prolific and dispersed by different species. Well-established premises for mammals have been governing fish research, but some contradictory findings suggest that knowledge translation between these animal groups needs prudence [e.g. the relative higher neurotoxicity of methylmercury (MeHg) vs. inorganic Hg (iHg)]. Biochemical/physiological differences between the groups (e.g. higher brain regeneration in fish) may determine distinct patterns. This review undertakes the challenge of identifying sensitive cellular targets, Hg-driven biochemical/physiological vulnerabilities in fish, while discriminating specificities for Hg forms.

SCOPE OF REVIEW

A functional neuroanatomical perspective was conceived, comprising: (i) Hg occurrence in the aquatic environment; (ii) toxicokinetics on central nervous system (CNS)/sensory organs; (iii) effects on neurotransmission; (iv) biochemical/physiological effects on CNS/sensory organs; (v) morpho-structural changes on CNS/sensory organs; (vi) behavioral effects. The literature was also analyzed to generate a multidimensional conceptualization translated into a Rubik's Cube where key factors/processes were proposed.

MAJOR CONCLUSIONS

Hg neurosensory toxicity was unequivocally demonstrated. Some correspondence with toxicity mechanisms described for mammals (mainly at biochemical level) was identified. Although the research has been dispersed by numerous fish species, 29 key factors/processes were pinpointed.

GENERAL SIGNIFICANCE

Future trends were identified and translated into 25 factors/processes to be addressed. Unveiling the neurosensory toxicity of Hg in fish has a major motivation of protecting ichtyopopulations and ecosystems, but can also provide fundamental knowledge to the field of human neurodevelopment.

Assessment of mercury contamination in Brycon falcatus (Characiformes: Bryconidae) and human health risk by consumption of this fish from the Teles Pires River, Southern Amazonia

ABSTRACT Brycon falcatus is one of the most highly consumed species of fish within the region in the Teles Pires basin, and has great commercial importance in sport and professional artisanal fishing. The objective of this study was to analyze the presence and concentration of total mercury (THg) in the muscle, liver and gills of B. falcatus, and calculate the risk to human health of THg contamination from ingestion of the fish. THg concentrations were similar in the liver (0.076 mg kg-1) and muscle (0.052 mg kg-1), and higher than in the gills (0.009 mg kg-1). The levels of HgT present in B. falcatus tissues did not influence weight gain and nutritional status. Based on the condition factor, weight and length ratio and hepatosomatic index, it seems that the concentrations of THg did not influence the health and well-being of B. falcatus collected in the Teles Pires River basin. THg concentrations in the muscle of B. falcatus are below the limit recommended by the World Health Organization for people who consume until 250 g of fish per week. The risk of deleterious effects on human health may exist if there is a greater consumption of B. falcatus such as 340 g/day, that is the mean of fish consumption by indigenous and riverine.

Post-breeding dispersal of frigatebirds increases their exposure to mercury

Migration and dispersal can expose wildlife to threats in different parts of their range, particularly for localized anthropogenic threats. Wildlife exposure to metal contaminants may correlate with local anthropogenic emissions. Feather mercury concentrations of adult and juvenile Lesser Frigatebirds (Fregata ariel) and Great Frigatebirds (F. minor) were determined for individuals breeding in the eastern Indian Ocean. Low mercury concentration in juveniles relative to adults, higher mercury concentration in adult females than adult males, and a trend for Lesser Frigatebirds to have higher mercury concentration than Great Frigatebirds implicate non-breeding ground exposure as the major influence on mercury burden. Aspects of foraging ecology are congruent with high exposure occurring in inshore waters of the non-breeding range, particularly in the South China Sea. These findings highlight the need for tighter mercury emission regulations in southeast Asia to minimise the potential threat to frigatebirds and other species dependent on marine resources including humans.

Simple analysis of total mercury and methylmercury in seafood using heating vaporization atomic absorption spectrometry

This study aimed to develop a simpler method for determining total mercury (T-Hg) and methylmercury (MeHg) in biological samples by using methyl isobutyl ketone (MIBK) in the degreasing step. The fat in the samples was extracted by MIBK to the upper phase. T-Hg transferred into the water phase. This was followed by the extraction of MeHg from the water phase using HBr, CuCl2 and toluene. The MeHg fraction was reverse-extracted into L-cysteine-sodium acetate solution from toluene. The concentrations of T-Hg and MeHg were determined by heating vaporization atomic absorption spectrometry. Certified reference materials for T-Hg and MeHg in hair and fish were accurately measured using this method. This method was then applied to determine T-Hg and MeHg concentrations in the muscle, liver and gonads of seafood for the risk assessment of MeHg exposure. The mean T-Hg and MeHg concentrations in squid eggs were 0.023 and 0.022 µg/g, and in squid nidamental glands 0.052 and 0.049 µg/g, respectively. The MeHg/T-Hg ratios in the eggs and nidamental glands of squid were 94.4% and 96.5%, respectively. The mean T-Hg and MeHg concentrations in the gonads of sea urchins were 0.043 and 0.001 µg/g, respectively, with a MeHg/T-Hg ratio of 3.5%. We developed an efficient analytical method for T-Hg and MeHg using MIBK in the degreasing step. The new information on MeHg concentration and MeHg/T-Hg ratios in the egg or nidamental glands of squid and gonads of sea urchin will also be useful for risk assessment of mercury in seafood.

Pollutant levels in discarded fish species by Spanish trawlers operating in the Great Sole Bank and the Atlantic coast of the Iberian Peninsula

Organic and inorganic pollutant levels were determined for the most discarded species from trawlers operating in Great Sole and Spanish coastal fishing grounds. Results for heavy metals indicated that Cd can reach values higher than legal limits for some species and tissues, while Hg and Pb concentrations are below established values. No significant variation was noticed with fishing grounds, but both season influences in the case of Pb and interspecies variation for Hg and Cd have been detected. Valorization recommendations could be therefore established according to the levels found in the different species.

Mercury and selenium intake by seafood from the Ionian Sea: A risk evaluation

The subject of the present study is the evaluation of the concentrations of mercury (Hg) and selenium (Se) in fish and shellfish from the Gulf of Catania (Ionian Sea) and the assessment of related risk-based consumption limits per single contaminant in adults and children. In contrast to the potential harm from Hg, Se is an essential element that is normally found in high levels in seafood. If the amount of Hg is high enough, it could bind Se and irreversibly inhibit selenium-dependent enzymes. Thus, adequate levels of Se need to be available to replace the amount of Se lost to Hg sequestration, thereby maintaining normal selenoprotein synthesis. Hg analysis was conducted using a flow injection analysis system coupled with an atomic adsorption spectrometer, and Se analysis was conducted using an inductively coupled plasma mass spectrometry (ICP-MS). Of the trace elements investigated, only Hg has a limit set by the European Community for human consumption, and this was never exceeded. Nevertheless, based on Target Hazard Quotient (THQ) over 1, and on the Estimated Daily Intake per meal (EDIm) higher than the Provisional Tolerable Intake (PTI) suggested by the Joint FAO/WHO Expert Committee on Food Additive (JECFA), Hg oral exposure derived from consumption of the benthonic fish and of the bigger pelagic fish species analyzed, could follow the occurrence of systemic effects. Se was found always in molar excess respect to Hg in all pelagic fish and in the shellfish, nearly equimolar in the benthonic fish. Determining the evidence that foods, such as pelagic fish, with high molar excess of Se, could contribute to replace the amount of Se bound to Hg and thereby maintaining normal selenoprotein synthesis, is useful for a better understanding of the seafood safety.

Deletion of the ubiquitin-conjugating enzyme Ubc2 confers resistance to methylmercury in budding yeast by promoting Whi2 degradation

Ubiquitin-conjugating enzymes involved in sensitivity to methylmercury in yeast were identified by deletion analysis, which showed that Ubc2- or Ubp13-deficiency conferred resistance to methylmercury. Whi2, which was previously shown to be associated with increased methylmercury toxicity and is intracellularly degraded via the ubiquitin-proteasome system, was expressed at significantly lower levels in Ubc2-deficient yeast than in wild-type yeast. Ubc2/Whi2 double-deficient yeast showed neither an additive nor synergistic increase in methylmercury resistance. Our results indicate that Ubc2 may increase the sensitivity to methylmercury in yeast by inhibiting the proteasomal degradation of Whi2.