Increase in anthropogenic mercury in marginal sea sediments of the Northwest Pacific Ocean

Mercury bioaccumulation and its relationship with trophic biomarkers in a Mediterranean elasmobranch mesopredator

Human activity has led to increased concentrations of mercury (Hg) in the world's oceans. Mercury can bioaccumulate and biomagnify in animal tissues via trophic transfer, thus, becoming most pronounced in larger and older predators. Here, we measured Hg concentrations and their relationship with stable isotopes-based proxies of trophic level (δ13C and δ15N values) in multiple tissues of Mustelus spp. from the Mediterranean Sea. We found higher Hg concentrations in muscle than in liver and fin tissues. The relationship between Hg concentrations and δ15N values in muscle suggested repeated foraging for low trophic level and Hg-poor prey, and biomagnification of Hg at higher trophic levels. Seasonal variations in δ13C values could indicate shifts in primary production sources and/or in local prey availability. The HBVSe index suggested no risk to human health, however the safe meal limit recommendations are 4.5 and 2.2 portions per month for adults and children, respectively.

Applying new regional background concentration criteria to assess heavy metal contamination in deep-sea sediments at an ocean dumping site, Republic of Korea

It is crucial to establish appropriate background concentrations to discern heavy metal pollution in the marine environment. In this study, we analyzed heavy metals in deep-sea sediment cores to determine regional background concentrations at the East-Sea Byeong Ocean dumping site. The vertical profiles of heavy metals were categorized into three groups based on their contamination characteristics, and regional background levels for 12 metals were determined using pre-1900 averages. The enrichment factor, contamination factor, and pollution load index, calculated using regional background concentrations, indicated significant contamination by Cr, Co, Cu, Zn, Cd, Hg, and Pb during the ocean dumping period. These results differ from those obtained using global average concentrations. This underscores the importance of considering regional characteristics to minimize the risk of misinterpreting anthropogenic impacts. The approach based on local information is considered useful when sediment quality guidelines are absent or inapplicable.

Impacts of the invasive Spartina anglica on C-S-Hg cycles and Hg(II) methylating microbial communities revealed by hgcA gene analysis in intertidal sediment of the Han River estuary, Yellow Sea

We investigated the impact of invasive vegetation on mercury cycles, and identified microorganisms directly related to Hg(II) methylation using hgcA gene in vegetated mud flats (VMF) inhabited by native Suaeda japonica (SJ) and invasive Spartina anglica (SA), and unvegetated mud flats (UMF) in Ganghwa intertidal sediments. Sulfate reduction rate (SRR) and rate constants of Hg(II) methylation (K_m) and methyl-Hg demethylation (K_d) were consistently greater in VMF than in UMF, specifically 1.5, 2 and 11.7 times higher, respectively, for SA. Both K_m and K_d were significantly correlated with SRR and the abundance of sulfate-reducing bacteria. These results indicate that the rhizosphere of invasive SA provides a hotspot for Hg dynamics coupled with sulfate reduction. HgcA gene analysis revealed that Hg(II)-methylators were dominated by Deltaproteobacteria, Chloroflexi and Euryarchaeota, comprising 37.9%, 35.8%, and 6.5% of total hgcA gene sequences, respectively, which implies that coastal sediments harbor diverse Hg(II)-methylating microorganisms that previously underrepresented.

Mercury geochemistry of marine sediments from the eastern Laptev Sea: The spatial distribution, levels, and contamination assessment

Twenty-seven sediment samples from the eastern Laptev Sea were analyzed for mercury and total organic carbon as well as grain-size distribution. The average total mercury (THg) concentrations in sediments are 29 ± 14 μg kg^-1. A significant correlation of THg content with total organic carbon and clay and silt fractions was shown. The ²¹⁰Pb-dated sediment core was used to evaluate the contamination degree and flux of THg in sediments from the eastern Laptev Sea. The average sedimentation rate for the all dated intervals was 0.17 cm/year. The THg flux increased from 20 to 28 μg/m²/year in the period of 1892-1950 to 53-59 μg/m²/year in the modern period of 2011-2015. According to various indices, the ecological risk from THg in studied sediment was low.

The timing and magnitude of anthropogenic mercury pollution: A 200-year record from multi-lake sediment cores in northeast China

The recent substantial expansion of human activities in northeast (NE) China has resulted in increased emission of environmental pollutants. Longer-term records of such environmental pollutants provide a benchmark against which it is possible to evaluate the nature, extent and timing of anthropogenic environmental changes. Based on measurements of mercury (Hg) concentrations and accumulation rates in 11 lake sediment cores from the Songnen Plain in NE China, we here present a reconstruction of the historical deposition of Hg as an indicator of the changing scale of human impact. The results demonstrate an increasing trend of Hg concentration, concurrent with elevated anthropogenic emissions, beginning from the early 1900s, accelerating through the mid-1950s and slightly decreasing from the late 1990s onwards. The increase in anthropogenic Hg coincides with the reform and opening up of China, which precipitated social and economic transformation, and rapid industrial and economic growth. Measurements of the Hg enrichment factor in all the cores enables identification of the anthropogenic contribution to Hg accumulation. The geoaccumulation index indicates that the lakes are in general moderately polluted by Hg. The historical trend of Hg accumulation rate parallels the temporal progression of biomass burning and fossil fuel consumption in the region. The findings elucidate the extent of anthropogenic pollution in the Anthropocene and underline the importance of identifying Hg sources to reduce emissions and guide the implementation of effective mitigation strategies.

Total mercury concentrations in sharks, skates and rays along the South African coast

Global declines in elasmobranch populations resulting from several stressors raises conservation concern. Additionally, apex predators bioaccumulate high concentrations of total mercury (THg), due to biomagnification. Although South Africa is considered one of the top ten contributors of Hg emissions globally, information on Hg concentrations in elasmobranchs is limited. The aim of this study was to evaluate the THg concentrations in 22 species of elasmobranchs along the South African coastline. Concentrations ranged between 0.22 and 5.8 mg/kg in Haploblepharus pictus (dark shysharks) and Rostroraja alba (white skates) on the south coast, respectively. Along the east coast it ranged between 0.21 and 17.8 mg/kg in Mobula kuhlii (shortfin devil rays) and Sphyrna lewini (scalloped hammerheads), respectively. Mercury concentrations on the east coast were in the same range or higher compared to the same species sampled between 2005-10 from the same region, with generally higher concentrations compared to the same species sampled globally.

Mercury contamination of sediments in an open coastal area of the Hupo Basin, East Sea, Korea

Mercury (Hg) contamination in open coastal areas has attracted public concern regarding safe fish consumption and management of the coastal environment, especially in areas of accidental Hg spills on inland coasts. This study investigated the temporal and spatial distribution of Hg in sediments of Youngil Bay and the Hupo Basin, East Sea, Korea; it also discussed the sources and transport of anthropogenic Hg. Hg hot spots were found in the northern Hupo Basin (elevated by 2-3×) and the river mouth area in Youngil Bay (elevated by approximately 70×). The river mouth contamination resulted from the destruction of a dam impounding landfill waste, while the basin contamination was attributed to atmospheric deposition and Hg enrichment associated with increased organic carbon concentrations driven by high biological production in the coastal upwelling area. Spilled Hg was transported to open coastal areas up to 36.6°N.

Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

Substantial accumulation of mercury in the deepest parts of the ocean and implications for the environmental mercury cycle

Anthropogenic activities have led to widespread contamination with mercury (Hg), a potent neurotoxin that bioaccumulates through food webs. Recent models estimated that, presently, 200 to 600 t of Hg is sequestered annually in deep-sea sediments, approximately doubling since industrialization. However, most studies did not extend to the hadal zone (6,000- to 11,000-m depth), the deepest ocean realm. Here, we report on measurements of Hg and related parameters in sediment cores from four trench regions (1,560 to 10,840 m), showing that the world's deepest ocean realm is accumulating Hg at remarkably high rates (depth-integrated minimum-maximum: 24 to 220 μg ⋅ m^-2 ⋅ y^-1) greater than the global deep-sea average by a factor of up to 400, with most Hg in these trenches being derived from the surface ocean. Furthermore, vertical profiles of Hg concentrations in trench cores show notable increasing trends from pre-1900 [average 51 ± 14 (1σ) ng ⋅ g^-1] to post-1950 (81 ± 32 ng ⋅ g^-1). This increase cannot be explained by changes in the delivery rate of organic carbon alone but also need increasing Hg delivery from anthropogenic sources. This evidence, along with recent findings on the high abundance of methylmercury in hadal biota [R. Sun et al, Nat. Commun. 11, 3389 (2020); J. D. Blum et al, Proc. Natl. Acad. Sci. U. S. A. 117, 29292-29298 (2020)], leads us to propose that hadal trenches are a large marine sink for Hg and may play an important role in the regulation of the global biogeochemical cycle of Hg.

Mercury and selenium in squids from the Pacific Ocean and Indian Ocean: The distribution and human health implications

Squids are globally distributed. Hg-contaminated squids may have high risks on humans. With abundant Se (antagonistic effect on Hg), the risks can be reduced. We collected squids around the world (Northwest Pacific Ocean, Southeast Pacific Ocean and Indian Ocean). Concentrations of Hg and Se were region-based and tissue-based. The higher content of Se were, the lower relative Hg levels were. The correlation between Se:Hg and Se was the strongest in the digestive gland. The values of Se:Hg and THQ all confirm that the health risk was lower in samples with higher concentrations of Se. Despite the risk assessment by Se:Hg, BRV and THQ analysis showed no risk when consumed in moderation, the maximum daily intake is provided based on Monte Carlo simulation. In future, when evaluating the risks cause by Hg exposure and providing the recommended daily amount, it may need to concurrent consideration of Se levels.

Observation-Based Mercury Export from Rivers to Coastal Oceans in East Asia

Globally, the consumption of coastal fish is the predominant source of human exposure to methylmercury, a potent neurotoxicant that poses health risks to humans. However, the relative importance of riverine inputs and atmospheric deposition of mercury into coastal oceans remains uncertain owing to a lack of riverine mercury observations. Here, we present comprehensive seasonal observations of riverine mercury and methylmercury loads, including dissolved and particulate phases, to East Asia's coastal oceans, which supply nearly half of the world's seafood products. We found that East Asia's rivers annually exported 95 ± 29 megagrams of mercury to adjacent seas, 3-fold greater than the corresponding atmospheric deposition. Three rivers alone accounted for 71% of East Asia's riverine mercury exports, namely: Yangtze, Yellow, and Pearl rivers. We further conducted a metadata analysis to discuss the mercury burden on seawater and found that riverine export, combined with atmospheric deposition and terrestrial nutrients, quantitatively elevated the levels of total, methylated, and dissolved gaseous mercury in seawater by an order of magnitude. Our observations support that massive amounts of riverine mercury are exported to coastal oceans on a continental scale, intensifying their spread from coastal seawater to the atmosphere, marine sediments, and open oceans. We suggest that the impact of mercury transport along the land-ocean aquatic continuum should be considered in human exposure risk assessments.

Pollution and ecological risk assessment, and source identification of heavy metals in sediment from the Beibu Gulf, South China Sea

The Beibu Gulf is an important passageway between China and the Association of Southeast Asian Nations, where there has been an increase in pollution of heavy metals (HMs). High concentrations of Pb, Cr, Cd, Cu, Zn, As, and Hg in surface sediment were found in Qinzhou Bay, Fangchenggang, and other coastal areas. Stochastic geo-accumulation analyses identified the pollution to be "uncontaminated"; however, it had an 18% probability of deterioration. The Cd, Hg, and As pollution were relatively serious. Principal component analysis, positive matrix factor model, and mercury isotopes demonstrated that the HMs could mainly be attributed to industrial sources including petrochemical, coal-fired, metal and metalloid processing, leather tanning, and human activities: anthropogenic sources accounted for approximately 70% of all the contaminations. This study demonstrates the contribution of terrigenous input to HMs even at a low level and provides basic data for the coordinated development of land and marine resources.

Datasets on the spatial distribution of mercury and its controlling factors in the Yellow Sea

Large amount of anthropogenic mercury (Hg) emitted from China has been transported and deposited in the northwestern Pacific marginal seas; in particular, the Yellow Sea adjacent to China is immediately affected by Chinese-high Hg emissions [1,2]. This article presents the comprehensive baseline dataset on the mercury concentrations and their controlling factors in surface sediments from the entire Yellow Sea shelf, including Korean and Chinese rivers and coastal zones. These data supported the research article entitled “Sedimentary mercury (Hg) in the marginal seas adjacent to Chinese High-Hg emissions: source-to-sink, mass inventory, and accumulation history” Kim et al. [1]. Some of the data was used in Kim et al.’s research paper [3] with the reference [1]. A total of 492 surface sediments were collected from the Yellow Sea shelf and coastal zones, and the rivers around the Sea. All sediment samples were freeze-dried and ground by agate mortar for analyzing total mercury (THg) and related elemental components (total nitrogen, total carbon, total inorganic carbon, total organic carbon, and aluminum). Most previous studies on the sedimentary Hg were conducted locally, mainly in the river-dominated coastal and inner shelf zones of the Yellow Sea, which are associated with riverine Hg inputs. Thus, the quality and quantity of available sedimentary Hg data, on which we rely for mass inventories of Hg in the Sea, are limited. In this respect, our large dataset may contribute significantly to a better understanding of the behaviors of riverine and atmospheric Hg from Chinese sources and will help to further refine global estimates of Hg discharge to ocean margins and open oceans in East Asia. Additionally, the dataset will be essential for improving numerical model for global budget calculation and prediction.

Correlation patterns between magnetic parameters and heavy metals of core sediments in the Yellow River Estuary and their environmental implications

The potential use of environmental magnetism to investigate heavy metal pollution was investigated by analyzing sediment samples from a short sediment core (Z07) from the Yellow River Estuary. The heavy metal concentrations and speciation, grain sizes, and magnetic properties were determined, and correlations between the parameters were identified. Strong exponential relationships were found between the Hg concentrations and χ_fd%, χ_ARM-20mT, and clay content. Linear correlations were found between the As, Cd, Co, Cr, Ni, Pb, and Zn concentrations and χ_fd%, χ_ARM-20mT, and clay content. This indicated that Hg was mainly sorbed to the surfaces of nano-sized magnetic and clay minerals and predominantly had anthropological sources but the other heavy metals had mineralogical and other natural sources. These conclusions were supported by the heavy metal fractionation results. Heavy metal concentrations in sediment at site Z07 have decreased markedly since 2003 in response to water and sediment regulations being implemented.

Mercury proxy for hydrothermal and submarine volcanic activities in the sediment cores of Central Indian Ridge

Hydrothermal vent is the one of the main natural Hg sources to the deep ocean. Thus, we investigated which Hg speciation in the sediment core can be the past records for geothermal activities in mid-ocean ridges of the Central Indian Ocean. The result showed that the hydrothermal Hg in the core sediments was mainly associated with Fe-Mn oxides with the elevated concentrations of other hydrothermal-derived trace metals [Co + Zn + Cu]. In addition, the [Sm]/[Nd] and [Rb]/[Sr] ratios and ɛNd_CHUR and ⁸⁷Sr/⁸⁶Sr isotopic values supported that the extremely high Hg concentrations were possibly originated from the hydrothermal vent. However, the Hg emitted from submarine volcano was mainly associated with sulfides-organic matters because the volcanos did not release Fe and Mn. Thus, our results showed that the sedimentary Hg is an independent toll for reconstruction of paleodynamics of hydrothermal and/or volcanic activities in deep sea basin of the Central Indian Ocean.

Bioaccumulation and trophic transfer of potentially toxic elements in the pelagic thresher shark Alopias pelagicus in Baja California Sur, Mexico

Pelagic thresher shark (Alopias pelagicus) is a circumglobal species with high ecological and economic importance. Concentrations of mercury, selenium and cadmium in the muscle and liver tissues of A. pelagicus captured from Baja California Sur, Mexico were determined for assessing the potential human hazard. Results revealed that the average concentrations of Hg (0.76 mg kg^-1) and Cd (0.18 mg kg^-1) in muscle tissues were below the maximum permissible limits for human consumption. Se in the muscles were relatively low (mean: 0.30 mg kg^-1 -1) resulting in a molar excess of Hg over Se. Average levels of hepatic Cd were extremely higher than the maximum limit for consumption. Organotropism of Hg was muscle > liver, whereas Se and Cd presented an order of liver > muscle. Biomagnification Factor (BMF) emphasized the trophic transfer of elements. Selenium Health Benefit value was negative (-3.76) posing potential health risks demanding regular monitoring for health risks.

Seasonality of Hg dynamics in the Ebrié Lagoon (Côte d'Ivoire) ecosystem: influence of biogeochemical factors

This study addresses the different biogeochemical parameters that control the dynamics of Hg, which is a less-studied metal in the Ebrié Lagoon. During two hydrological seasons, the dry season and the rainy season, we regularly sampled and analysed various compartments (e.g. sediments and fishes (Tilapia sp.)) of the lagoon. Thus, the physicochemical parameters were measured in situ (e.g. temperature, pH, salinity, redox potential and dissolved oxygen, total dissolved organic carbon, nitrates and sulphates), and the microbiological parameters (e.g. cultivable cells, total enzymatic activity and catabolic activity) were measured to establish the seasonal variations in the links between Hg and biogeochemical parameters through multivariate statistical analyses. The bioavailability of Hg from an unpolluted site was studied by comparing the ratios of fish and sediment. The results indicated that the seasons influenced the different biogeochemical factors, although for some factors, the variations were not significant. This influence was more pronounced in the dry season than in the rainy season. The impact of microbial activities and organic matter on Hg dynamics was observed in all seasons. However, other factors, such as pH, temperature, salinity, Eh and sulphates, influenced the dynamics of Hg only in the dry season.

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 ± 15 ng g^-1) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km³ yr^-1) and organic carbon accumulation rates (9.3 ~ 49.4 g m^-2 yr^-1) were elevated compared to other fjords. Furthermore, the δ¹³C (-27 ~ -24‰) and δ³⁴S values (-10 ~ 15‰) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more OM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems.

Vertical distributions of mercury in marine sediment cores from central and southern part of Bohai Sea, China

In past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, four representative 210Pb-dated sediment cores were collected in the central and southern part of Bohai sea to investigate vertical changes of Hg contents and explore the relationship between the Hg deposition and pollution history in this region utilizing a large amount of information available. The results indicated that Hg median concentrations of sediment core B62, B66, JQ17 and HZ24 were 0.043 mg/kg, 0.054 mg/kg, 0.033 mg/kg and 0.018 mg/kg respectively, among which, B66 in Yellow river estuary and B62 in central part of Bohai Sea had higher concentrations and HZ24 in Bohai Strait had a lower concentration. 210Pb profile appeared as a three segments model in the core B62, but as many steps of decay with depth in B66. For HZ24, 210Pb activity only fluctuated with depth without any discernible trend. Sedimentary rates of these cores decreased as follows: B66＞B62＞JQ17＞HZ24. Vertical distributions of Hg concentrations in sediment cores were totally different from each other. Hg concentrations in sediment core B62 experienced an initial fluctuation followed by a decreasing trend, while sediment core HZ24 almost showed the uniform decreasing trends from the surface to the bottom. There were three segments of variation in sediment cores JQ17: initial fluctuation followed by an obviously decreasing tendency and then a converted variation from surface to bottom. Hg contents changes in core B62 might reflect the additive effects from atmospheric deposition at a larger scale and the river-delivered sediment accumulation, while Hg vertical changes in B66 mainly had a close relationship with the input of Yellow river. The converted variation at the bottom section in sediment cores JQ17 was inferred to have some relationship with the Chengbei platform construction in the corresponding periods.