Critical review of mercury contamination in Sri Lankan fish and aquatic products

Mercury levels in freshwater aquatic products across China: Spatial distribution, species differences, and health risk assessment

Freshwater product consumption is a major source of mercury (Hg) exposure in China. This study analyzed Hg concentrations in 12,560 samples from 29 provinces across China (2010-2021) and conducted probabilistic health risk assessments across various life stages. The average Hg concentration in China's freshwater products was 40.9 ± 32.3 ng/g (wet weight), lower than global averages. However, certain species, Gymnocypris and Schizothoracids from Tibet, exhibited elevated levels (216.2 ± 84.2 ng/g and 156.7 ± 89.9 ng/g, respectively). The estimated dietary intakes (EDIs) of MeHg for all age groups were well below the JECFA threshold of 1.6 μg/kg BW, even at the P95 exposure level. However, long-term exposure assessments revealed elevated risks for children aged 2-12, with Target hazard quotients (THQ) values exceeding 1 at the P95 exposure level, particularly among younger children aged 2-7. Spatially, elevated Hg exposure risks were identified in Hong Kong, Zhejiang, Guizhou, and the Songhua River regions, with contamination in Zhejiang tied to the compact fluorescent lamp industry. Furthermore, prenatal MeHg exposure through freshwater product consumption was estimated to result in Intelligence Quotient (IQ) losses of 0.00548-0.193 points in infants. These findings underscore the need for targeted interventions to mitigate Hg exposure and provides recommendations for safer freshwater fish selection in the Chinese market.

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.

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Comparative Study on the Distribution of Essential, Non-Essential Toxic, and Other Elements across Trophic Levels in Various Edible Aquatic Organisms in Sri Lanka and Dietary Human Risk Assessment

Thirty-six elements are categorized as essential but toxic in excess amount (EBTEs), non-essential toxic (NETs), and Other in 29 different edible aquatic species dwelling in offshore pelagic, and coastal and estuarine (CE) ecosystems were investigated in Sri Lanka. Elements were analyzed using an energy-dispersive X-ray fluorescence (EDXRF) spectrometer, and an NIC MA-3000 Mercury Analyzer. EBTEs showed a negative relationship, whereas NETs showed a positive relationship between the concentration (mg/kg wet weight) and trophic levels in both ecosystems. EBTEs showed trophic dilution, whereas NETs showed trophic magnification. Some elements in a few organisms exceeded the maximum allowable limit which is safe for human consumption. There was a positive relationship (R² = 0.85) between the concentration of mercury and body weight of yellowfin tuna (YFT). For the widely consumed YFT, the calculated hazard index (HI) for the non-carcinogenic health and exposure daily intake of NETs for adults were 0.27 and 9.38 × 10^-5 mg/kg bw/day, respectively. The estimated provisional tolerable weekly intake (PTWI) (μg/kg bw/w) was 0.47 for arsenic and 0.05 for antimony, cadmium, mercury, and lead. The HI and PTWI values were below the recommended limits; thus, consumption of YFT does not pose any health risk for Sri Lankan adults.

Mitigating the impact of mercury contaminants in fish and other seafood-A review

Mercury (Hg) is a well-known toxicant which enters the marine environment by both natural and anthropogenic sources. Consumption of fish and other seafood that contain methylmercury (MeHg) is a leading source of Hg exposure in humans. Considerable efforts have been made to mitigate the Hg presence and reduce its risks to humans. In this review the acknowledged methods of mitigation are summarized such as regulation and maximum allowable limits, and culinary treatments. In addition, selected industrial level trials are reviewed, and studies on Hg intoxication and the protective effects of the essential trace element, selenium (Se), are discussed. In view of the available literature, Hg reduction in fish and other seafood on a large industrial scale still is largely unsuccessful. Hence, more research and further attempts are necessary in order to better mitigate the Hg problem in fish and other seafood products.

A Quantitative Assessment and Biomagnification of Mercury and Its Associated Health Risks from Fish Consumption in Freshwater Lakes of Azad Kashmir, Pakistan

Issues regarding biomagnification of mercury (Hg) due to its persistence, bioaccumulation, and toxicity in freshwater lakes have gained much attention in the last two decades especially in remote regions of the world where anthropogenic inputs are considered as negligible. In this study, spatial distribution of total mercury (THg), interspecific accumulation patterns, trophic transfer, and associated health risks in fish of freshwater lakes (357-3107 masl) in Azad Kashmir, Pakistan, were investigated. THg concentrations in the regions were 0.20 ± 0.08 μg g^-1 in glacial, 0.54 ± 0.21 μg g^-1 in rural, and 1.35 ± 0.46 μg g^-1 in urban region. Omnivorous, herbivorous, and carnivorous fish showed THg concentrations of 0.94, 0.85, and 0.49 μg g^-1. Regional, lake, trophic level, and specie-specific differences of THg accumulation were found significant in the study. Among growth parameters, length and age varied significantly among species, trophic levels, and lakes, whereas weight showed significant variation among lakes as well. Condition factor (K) showed significant differences within species, lakes, and trophic levels. Biomagnification was observed in all lakes with the trophic magnification slopes (TMS) ranging from 0.03 to 0.20 with an average of 0.094 ± 0.07. Isotopic values of nitrogen (δ¹⁵N) and condition factor were found to dominate THg accumulation trends; however, no significant health risks were found in the study.

Potentially Toxic Elements (PTEs) in the Fillet of Narrow-Barred Spanish Mackerel (Scomberomorus commerson): a Global Systematic Review, Meta-analysis and Risk Assessment

The contamination of seafood like narrow-barred Spanish mackerel (Scomberomorus commerson) fillets by potentially toxic elements (PTEs) has converted to worldwide health concerns. In this regard, the related citations regarding the concentration of PTEs in fillets of narrow-barred Spanish mackerel were collected through some of the international databases such as Scopus, Cochrane, PubMed, and Scientific Information Database (SID) up to 10 March 2020. The concentration of PTEs in fillets of narrow-barred Spanish mackerel fish was meta-analyzed and the health risk (non-carcinogenic risk) was estimated by the total target hazard quotient (TTHQ). The meta-analysis of data indicated that the rank order of PTEs in fillet of narrow-barred Spanish mackerel was Fe (10,853.29 μg/kg-ww) > Zn (4007.00 μg/kg-ww) > Cu (1005.66 μg/kg-ww) > total Cr (544.14 μg/kg-ww) > Mn (515.93 μg/kg-ww) > Ni (409.90 μg/kg-ww) > Pb (180.99 μg/kg-ww) > As (93.11 μg/kg-ww) > methyl Hg (66.60 μg/kg-ww) > Cd (66.03 μg/kg-ww). The rank order of health risk assessment based on the country by the aid of TTHQ for adult consumers was Malaysia (0.22251) > Philippines (0.21912) > Egypt (0.08684) > Taiwan (0.07430) > Bahrain (0.04893) > Iran (0.03528) > China (0.00620) > Pakistan (0.00316) > Yemen (0.00157) > India (0.00073). In addition, the rank order of health risk assessment based on the country by the aid of TTHQ for child consumers was Malaysia (1.03838) > Philippines (1.02257) > Egypt (0.40523) > Taiwan (0.34674) > Bahrain (0.22832) > Iran (0.16466) > China (0.02892) > Pakistan (0.01474) > Yemen (0.00731) > India (0.00340). Therefore, the children in Malaysia and the Philippines were at considerable non-carcinogenic risk. Hence, approaching the recommended control plans in order to decrease the non-carcinogenic risk associated with the ingestion of PTEs via the consumption of narrow-barred Spanish mackerel fish fillets is crucial.

Metal Contents in Fish from the Bay of Bengal and Potential Consumer Exposure-The EAF-Nansen Programme

Fish represent an important part of the Sri Lankan and Bangladeshi diet. However, fish is also a source of contaminants that may constitute a health risk to consumers. The aim of this study was to analyse the contents of arsenic, cadmium, mercury, and lead in 24 commonly consumed marine fish species from the Bay of Bengal and to assess the potential health risk associated with their consumption. Mercury and lead contents did not exceed the maximum limits for any of the sampled species, and consumer exposure from estimated daily consumption was assessed to be minimal for adults and children. Numerous samples exceeded the maximum limit for cadmium (58%), particularly those of small size (≤25 cm). However, consumer exposure was insignificant, and health assessment showed no risk connected to consumption. These data represent an important contribution to future risk/benefit assessments related to the consumption of fish.

How much fluctuating asymmetry in fish is affected by mercury concentration in the Guanabara Bay, Brazil?

This study aims to analyze if the fluctuating asymmetry (FA) of the Corocoro grunt Orthopristis ruber is affected by mercury concentration in Brazilian Southeastern eutrophicated bay. The O. ruber fishes were collected in two areas of the Guanabara Bay, Rio de Janeiro, Brazil: Vermelha Beach, influenced to ocean waters, and Paquetá Island, for greater freshwater loads of the rivers of the region, both in wet and dry seasons. Possibly availability of food resources, exposure to other pollutants and harmful agents (pesticide, algal toxicity, among others), and environmental and oceanographic factors may be reflecting on the FA detected for the O. ruber population. Mercury (Hg) is a harmful trace metal when present in the food, because of the high toxicity, high levels of absorption, and low excretion rate. Hg accumulates in human organisms through fish consumption, which may represent a risk to health. Analytical determinations of THg were performed by Direct Mercury Analyzer, following the manufacture's recommendations and following the procedure proposed by Guimarães et al. (Food Sci Nutr 4:398-408, 2015). No evidenced in the influence of THg on FA. In turn, the THg was significantly different between areas. Higher THg levels were found in O. ruber populations in the Vermelha Beach, with mean values ​​of HgT 0.08 ± 0.01 mg/kg^-1, and the Paquetá Island with HgT 0.05 ± 0.01 mg/kg^-1. Likely higher THg on the Vermelha Beach occurred due to hydrodynamic factors, increasing the bioavailability of THg from the sediment and incorporated into the food web. This indicates that the higher THg levels in the outermost area of the Guanabara Bay can directly influence the bioaccumulation of this metal in the commercially important species present in this region, through the trophic chain because O. ruber constitutes an important part of the diet of themselves.

Water temperature modulates mercury accumulation and oxidative stress status of common goby (Pomatoschistus microps)

Mercury (Hg) is a widespread pollutant across estuarine and coastal areas, raising concern on its potential impact on aquatic organisms. Hg may origin from natural and anthropogenic sources, being persistent and potentially toxic to biota, ultimately representing a serious risk to human health. Hg accumulation and toxicity may also induce reactive oxygen species (ROS) production in marine organisms, responsible for cell and tissue damage. Additionally, the temperature is undoubtedly an important environmental factor to consider regarding accumulation, due to its marked influence on the physiology and ecology of aquatic organisms. This study aimed to investigate the effect of different temperature scenarios (15, 20 and 25 °C) on the Hg accumulation in Pomatoschistus microps (Krøyer, 1838) liver and muscle, as well as on oxidative stress responses and energy metabolism, after short-term exposure to a naturally contaminated sediment with an environmentally relevant [Hg] (1.2 μg g^-1). The results showed that Hg accumulation tends to increase along the temperature gradient with higher values of Hg accumulated in liver than in muscle tissue. The action of antioxidant enzymes and stress proteins seems to be effective in combating oxidative stress in the liver. Despite the action of antioxidant defences in the muscle, oxidative damage was observed at the protein level concomitantly with a decrease in aerobic energy production after exposure to Hg at higher temperatures. These findings are ecologically relevant and highlight the importance of further investigation of combined effects of Hg and other stressors, especially in a scenario of a changing climate where events leading to rapid alterations on water parameters are more frequent.

Mercury speciation in edible seaweed by liquid chromatography - Inductively coupled plasma mass spectrometry after ionic imprinted polymer-solid phase extraction

In contrast to most of essential and heavy metals, mercury levels in seaweed are very low, and pre-concentration methods are required for an adequate total mercury determination and mercury speciation in this foodstuff. An ionic imprinted polymer-based solid phase extraction (on column) pre-concentration procedure has been optimized for mercury species enrichment before liquid chromatography hyphenated with inductively coupled plasma mass spectrometry determination. The polymer has been synthesized by the precipitation polymerization method and using a ternary pre-polymerization mixture containing the template (methylmercury), a non-vinylated monomer (phenobarbital), and a vinylated monomer (methacrylic acid). Factors affecting the adsorption/desorption of Hg species (extract pH, loading and elution flow rates, volume of eluent, etc.), and parameters such as breakthrough volume and reusability, were fully studied. Mercury species were first isolated from seaweed by ultrasound assisted extraction using a 0.1% (v/v) HCl, 0.12% (w/v) l-cysteine, 0.1% (v/v) mercaptoethanol solution. Under optimized conditions, the limits of detection were 0.007 and 0.02 μg kg^-1 dw for methylmercury and Hg(II), respectively. The pre-concentration factor (volume of 10 mL of seaweed extract) was 50. Repeatability and reproducibility of the method were satisfactory with relative standard deviations lower than 16%. The proposed methodology was finally applied for the selective pre-concentration and determination of methylmercury and Hg (II) in a BCR-463 certified reference material and in several edible seaweeds.

Trace element concentrations in six fish species from freshwater lentic environments and evaluation of possible health risks according to international standards of consumption

Multi-element concentrations (Al, As, Cd, Cr, Hg, Ni, Pb, Se, and Sr) were analyzed in the muscle of six fish species (Hoplias malabaricus, Oligosarcus jenynsii, Rhamdia quelen, Bryconamericus iheringii, Astyanax fasciatus, and Odontesthes bonariensis) with different diets and habits from the Río Tercero Reservoir (RTR) in Córdoba, Argentina, during the wet and dry seasons. Besides, potential human health risks, associated with the consumption of these elements, have been assessed considering the average daily intake (EDI) in children and adults. Additionally, the target hazard quotient (THQ) and carcinogenic risk (CR) were evaluated taking into account the intake by the general population, fishermen, and consumption frequency recommended by the American Heart Association (AHA), the maximum scientific reference in cardiology in the USA and worldwide. All species presented quantifiable values in muscle for all the analyzed elements (Al, As, Cr, Hg, Ni, Se, and Sr), except for Cd and Pb, being Al and Sr the most accumulated elements in all species in both seasons. The consumption of edible muscles of the species studied in this reservoir represents a toxicological risk to humans. Mercury and As were the main elements that presented a health risk through the consumption of fish. Their concentrations in most fish species were above the maximum daily allowable concentrations, and THQ values were several times greater than 1. In addition, according to AHA recommendations, the cancer risk caused by As was greater than the acceptable value of 10^-4 in all species studied, and in both seasons, with the exception of A. fasciatus, in the rainy season. These results indicate that the consumption of fish from the RTR exposes the inhabitants to possible health risks, especially when considering the consumption frequency recommended by the AHA. Therefore, fish intake from this reservoir should be limited to minimize potential risks to the health of consumers. Finally, the results of this study are useful for controlling pollution and developing preventive and palliative policies to protect populations in contact not only with the reservoir but also with other areas of the world with similar conditions.

MerP/MerT-mediated mechanism: A different approach to mercury resistance and bioaccumulation by marine bacteria

Currently, mechanism underlying mercury resistance and bioaccumulation of marine bacteria remains little understood. A marine bacterium Pseudomonas pseudoalcaligenes S1 is resistant to 120 mg/L Hg²⁺ with bioaccumulation capacity of 133.33 mg/g. Accordingly, Hg²⁺ resistance and bioaccumulation mechanism of S1 was investigated at molecular and cellular level. Annotation of S1 transcriptome reveals 772 differentially expressed genes, including Hg²⁺-relevant genes merT, merP and merA. Both merT and merP gene have three complete copies in S1 genome, while merA gene has only one. In order to evaluate the function of these Hg²⁺-relevant genes, three recombinant strains were constructed to express MerA (named as A), MerT/MerP (TP) and MerT/MerP/MerA (TPA), respectively. The results show that Hg²⁺ resistance of strain TP, TPA, and A are improved with minimum inhibition concentration (MIC) being 60 mg/L, 40 mg/L, and 20 mg/L, respectively compared to 2 mg/L of host strain. Strain TP and TPA exhibit enhanced Hg²⁺ bioaccumulation capacity, while strain A does not differ from the control. Their equilibrium Hg²⁺ bioaccumulation capacities are 110.48 mg/g, 94.49 mg/g, 83.76 mg/g and 82.29 mg/g, respectively. Summarily, different from most microorganisms that exhibit Hg²⁺ resistance by MerA-mediated mechanism, marine bacterium S1 achieves Hg²⁺ resistance and bioaccumulation capability via MerT/MerP-mediated strategy.

Total mercury and methylmercury concentrations in native and invasive fish species in Shadegan International Wetland, Iran, and health risk assessment

Human exposure to mercury (Hg) mainly occurs through consumption of aquatics, especially fish. In aquatic systems, the bioaccumulation of Hg across trophic levels could be altered by invasive species through changing community composition. The present study is aimed at measuring total mercury (T-Hg) and methylmercury (MeHg) concentrations in non-native (redbelly tilapia (Tilapia zillii)) and native (Benni (Mesopotamichthys sharpeyi) and common carp (Cyprinus carpio)) fish species throughout Shadegan International Wetland and comparing health risk of their mercury contents to the local population. The concentrations were measured using a direct mercury analyzer (DMA 80). The average values of T-Hg and MeHg for native fishes were 19.8 and 10.49 μg/kg. These concentrations for the invasive fish were 28 and 14.62 μg/kg respectively. Despite having less length and weight than the native fish species, tilapia showed significantly higher T-Hg content, yet the lowest concentration of MeHg was observed in common carp with larger body length and weight. Concerning mercury health risk to consumers, tilapia demonstrated the highest estimated weekly intake (EWI) and percentages of tolerable weekly intake (%TWI) for both T-Hg and MeHg, while the highest hazard quotient (HQ) values were obtained for tilapia and Benni. Taken together, the mercury concentrations in the two native and non-native fishes were acceptable according to the international safety guidelines although the local people shall be warned for consumption of tilapia. Furthermore, the low calculated value of tissue residue criterion (TRC) for the wetland fishes sounds a warning.