Significant elevation of human methylmercury exposure induced by the food trade in Beijing, a developing megacity

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.

Occurrence, bioaccumulation, and ecological and health risks of Cd, Sn, Hg, and Pb compounds in shrimp and fish from aquaculture ponds

Aquaculture organisms may accumulate metals to induce health risks. Compared with the focus on total contents, chemical-specific risk assessment makes reasonable but is rare. Herein, we elucidated occurrence of twelve metal compounds in shrimp and fish (edible muscle, one of major metal-containing and generally targeted organs), water, sediment, and feedstuff from two aquaculture ponds in Zhejiang Province (one of the major aquatic production and consumption areas). We detected Cd(II) (0.6 -71.4 μg kg-1 in 100 % prawn but 63 % fish), methylmercury (MeHg, 0.5 -7.1 μg kg-1 in 100 % fish but 61 % shrimp), Pb(II) (0.4 -1.0 μg kg-1 in 57 % fish and 39 % prawn), and trimethyltin and triethyltin (0.4 -0.7 μg kg-1), which were much lower than the maximum limits in China. Pb(II), Cd(II), and Hg(II) up to 0.38 mg kg-1 were main contaminants in sediment while Cd(II) and Pb(II) up to 0.44 mg kg-1 were major contaminants in feedstuff compared with Cd(II), Sn(II), Hg(II), and Pb(II) majored in water at ng L-1 levels. Ecological risks were low in water but high for tributyltin in sediment. Additionally, light bioaccumulation of Cd(II) from sediment for prawn and methylmercury from feedstuff/sediment for crucian and bighead carp was induced. We also found light health risk of triethyl- and trimethyl lead, and Cd(II) (to children) associated with fish/shrimp consumption (edible muscle). This study proved high necessity of chemical-specific assessment, and shall trigger increasing interest to more metallic compounds in a wide range of uncultured and cultured plants and animals.

China's municipal wastewater policies enhanced seafood safety and offset health risks from atmospheric mercury emissions in the past four decades

The neurotoxin methylmercury in seafood threatens food safety worldwide. China has implemented stringent wastewater policies, established numerous treatment facilities and enforced rigorous water quality standards to address pollution in its waterways. However, the impact of these policies on seafood safety and methylmercury exposure remains unknown. Here we developed a process-based model showing that, although mercury reductions from municipal wastewater policies accounted for only 9% of atmospheric mercury emissions during 1980-2022, these measures unexpectedly prevented102,000 - 6,600 + 11,000 mercury-related deaths and counteracted nearly two thirds of potential deaths from those emissions. Furthermore, these policies ensured that146 - 9 + 8 megatonnes of freshwater seafood met the World Health Organization and China's mercury-safety standards, preventing US $ 498 - 29 + 32 billion in economic losses. Finally, we explore how China, as the primary global seafood producer and exporter, could develop municipal wastewater policies at the regional level to reduce aquatic pollutants and unlock the health benefits of seafood consumption.

Tracking and optimizing toxic chemical exposure pathways through food trade: A case study in SCCPs contaminated seafood in China

Food safety is related to human health and sustainable development. International food trade poses food safety risks through the collateral transport of toxic chemicals that are detrimental to human health. Domestic interprovincial trade has similar effects within countries but has not been comprehensively investigated previously. Here, we assessed the effects of interprovincial trade on food safety and human dietary exposure to short-chain chlorinated paraffins (SCCPs), a group of emerging persistent toxic chemicals, in seafood across China by synthesizing data from field observation and various models. Our findings indicate that there is a higher level of SCCPs exposure risk in coastal provinces compared to inland provinces. Approximately, 70.3% of human exposure to SCCPs through seafood consumption in China was embodied in the interprovincial seafood trade in 2021. Specifically, the domestic trade led to a remarkable increase in SCCPs exposure in the coastal provinces in South China, attributable to low SCCPs pollution in these provinces and imported seafood from those provinces with high SCCPs pollution. In contrast, human exposure to SCCPs decreased in those coastal provinces in East China due to importing seafood from those provinces with low SCCPs concentrations. The interprovincial seafood trade routes were optimized by linear programming to minimize human exposure to SCCPs considering both shipping cost and health risk constraints. The optimized trade routes reduced the national per capita SCCPs exposure through seafood consumption by over 12%. This study highlights the importance of interprovincial food trade in the risk assessment of toxic chemicals.

Dietary shifts drive the slowdown of declining methylmercury related health risk in China

Chinese population suffers severe health risk from dietary methylmercury (MeHg) exposure. However, the temporal change of such risk and socioeconomic driving factors remain unknown. This study investigates this issue by compiling time-series inventory of China's MeHg-related health risk at the provincial scale and revealing critical socioeconomic influencing factors through structural decomposition analysis. Results show that the per-fetus IQ decrements from dietary MeHg exposure have declined by 60% nationally during 2004-2019. Such decline results from the joint effects of dietary shifts (contributing 44%) and the decrease of MeHg concentrations in foods consumed (contributing 56%). However, the declining trend has slowed down since 2014 and even leveled off after 2016, which is mainly affected by dietary pattern changes. Especially, the increased intake level and proportion of fishes in underdeveloped provinces of China have dominated the slowdown of declining trend after 2016. Moreover, the affluence and education levels have significantly negative associations with per-fetus IQ decrements. Rich and well-educated people have higher ability of risk perception, which indicates the importance of rational consumption patterns. Our findings can help develop socioeconomic regulatory policies on reducing per-fetus IQ decrements from dietary MeHg exposure in China.

Emissions leakage embodied in inter-provincial trade brings unexpected air quality and health benefits

Inter-provincial trade can bring "emission leakage", and consequently influence the air quality and public health. However, there has been a lack of systematic research on air pollution and public health related to emission leakage embodied in inter-provincial trade of China. Here, we systematically evaluated for the first time the influence of emission leakage on national air pollution and related premature deaths in 2012 of China. Unexpected opposite influences of emission leakage on emission and air quality/public health were discovered. Emission leakage embodied in inter-provincial trade in 2012 of China led to an increase of 1.4 % to 4.8 % in national air pollutant emissions, but a decrease of 1.5 % (-0.8 μg·m-3) in population-weighted concentration of PM2.5, while avoiding 1.1 % (-1.4 × 104 people) of premature deaths. Therefore, to reveal the intrinsic mechanism of this opposite influences, we proposed two coefficients, the Concentration per unit primary PM2.5 emission (CPE, unit: μg·m-3/t) and the Death per unit primary PM2.5 emission (DPE, unit: people/t), to characterize the response of air quality and health to emission leakage embodied in inter-provincial trade. Statistical analysis indicated that both the above coefficients showed significant negative correlation (P < 0.05) with provincial PM2.5 emissions changes. The findings offer a means of adjustment and its related evaluation parameters for the emission transfer caused by inter-provincial trade, thereby contributing to further improvement environmental and health benefits through inter-provincial trade.

Significant impacts of river inputs on the distributions and transports of mercury and methylmercury in nearshore and open seas - Simulation based on field surveys and mass balance modeling

Rivers are important sources of Hg for adjacent seas, and seafood from nearshore waters is a major source of Hg exposure for humans. There is thus a key scientific concern regarding how much riverine Hg inputs influence Hg loads in nearshore waters as well as how far the impact range can extend from the river to the open sea. In addition, it is important to understand the influence of anthropogenic hydro-facilities and activities on Hg levels in downstream seas. Because of the concise mass exchange pattern between the seas and the previously demonstrated intensive Hg inputs under anthropogenic regulation from the Yellow River, the Bohai and Yellow Seas, which are key fishery and marine breeding areas for China, are an ideal research area for exploring the impacts of riverine Hg on nearshore and adjacent open seas. Field surveys were conducted in eight major rivers and two seas, and 433 water samples were collected. The main Hg input and output terms (rivers, ocean currents, underground discharge, sewage, coastal erosion, atmospheric deposition, surface evasion, sedimentation, and fisheries) were quantified in the Bohai and Yellow Seas. Owing to the high inputs from the Yellow and Yalu Rivers, elevated THg concentrations were found. Apart from direct MeHg discharge, riverine nutrients may also seemingly affect nearshore MeHg. Using mass balance models, we found that the Yellow River (9.8 t) was the dominant Hg source in the Bohai Sea, which accounted for more than half of all contributions, and the Bohai Sea played the role of a secondary source of Hg to the Yellow Sea, with a flux of 3.3 t. Anthropogenic hydro-activities in large rivers could significantly influence Hg outputs and loads in the nearshore and even open seas. This study provides useful information for water resource management applications to reduce potential MeHg risks.

International trade shapes global mercury-related health impacts

Mercury (Hg) is a strong neurotoxin with substantial dangers to human health. Hg undergoes active global cycles, and the emission sources there of can also be geographically relocated through economic trade. Through investigation of a longer chain of the global biogeochemical Hg cycle from economic production to human health, international cooperation on Hg control strategies in Minamata Convention can be facilitated. In the present study, four global models are combined to investigate the effect of international trade on the relocation of Hg emissions, pollution, exposure, and related human health impacts across the world. The results show that 47% of global Hg emissions are related to commodities consumed outside of the countries where the emissions are produced, which has largely influenced the environmental Hg levels and human exposure thereto across the world. Consequently, international trade is found to enable the whole world to avoid 5.7 × 10⁵ points for intelligence quotient (IQ) decline and 1,197 deaths from fatal heart attacks, saving a total of $12.5 billion (2020 USD) in economic loss. Regionally, international trade exacerbates Hg challenges in less developed countries, while resulting in an alleviation in developed countries. The change in economic loss therefore varies from the United States (-$4.0 billion) and Japan (-$2.4 billion) to China (+$2.7 billion). The present results reveal that international trade is a critical factor but might be largely overlooked in global Hg pollution mitigation.

Human exposure to phthalate esters in soils embodied in interregional food trade in China

The ubiquitous occurrence of phthalate esters (PAEs) in agricultural soil results in their inevitable accumulation in crops, potentially increasing the risk of human exposure to PAEs via daily food intake. Dietary health risk of PAEs not only depends on locally produced food but also the imported food from other regions. However, the impact of interregional food trade on human dietary exposure to PAEs has been seldom assessed. Herein, we investigated the impact of interregional food trade on the dietary exposure to PAEs that contributed from soil contamination in China. The average daily dietary intake of PAEs for the Chinese general population was 24.3 μg/kg/day when assuming the total consumption of crops from local market only, while the average daily dietary intake of PAEs for the Chinese general population was decreased by 2.9% when the effects of interregional food trade were involved into the calculation. Additionally, the interregional food trade remarkably increased the daily dietary intake of PAEs in the regions of Beijing-Tianjin region (47.8%), North (21.4%) and Central (4.26%). As a result, the hazard quotient value of PAEs in the regions of Beijing-Tianjin region, North and Central increased by 29.4%, 11.0% and 5.0%, respectively, owing to the consumption of imported crops from the highly PAEs contaminated regions. In contrast, the daily intake and hazard quotient value of PAEs in the regions of Central Coast, Northwest, Northeast and South Coast decreased due to the interregional trade. These results indicated that the interregional food trade promoted the transfer of PAEs between regions and thus altered the potential risk to the local population. Overall, this study highlights the importance of taking the interregional food trade into account to provide a more accurate risk assessment of dietary exposure to pollutants.

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.

Human Methylmercury Exposure and Potential Impacts in Central Tibet: Food and Traditional Tibetan Medicine

Methylmercury presents potent neurotoxicity to humans. Fish consumption is the leading source of human exposure to methylmercury worldwide. However, the exposure source in Tibet remains poorly understood because of the scarcity of observational data on most Tibetan foods, although high mercury levels were recently detected in some traditional Tibetan medicines. Here, the results of field investigations show that the joint consumption of traditional Tibetan medicines (TTMs), fish, and rice constitutes a primary exposure pathway to methylmercury in Tibetans and that the probable daily intake of methylmercury is close to that for many coastal regions. People who are young and high-income may have higher methylmercury exposure levels mainly because of economic development and cultural exchanges among regions. Our analysis indicates that a large proportion of the Tibetan population are likely to face a high methylmercury exposure risk and that mercury-susceptible populations in Tibet should be attentive to consuming TTMs with fish.

Biotransport of mercury and human methylmercury exposure through crabs in China - A life cycle-based analysis

Exposure to methylmercury (MeHg) has various toxic effects on humans. The evaluation of human MeHg exposure has previously focused on fish consumption. However, in this study, we found that MeHg levels in domestic crabs in China were also relatively high (range: 50-1400 ng/g, dry weight). The high MeHg levels in crabs and their high consumption do not match the risk assessment of MeHg, indicating an underestimated exposure risk, especially in MeHg-sensitive groups such as pregnant women. The annual crab MeHg content output in China was estimated to be 30 ± 27 kg. A total of 6.8% of the country's land area contributes 71% of the MeHg output. However, 66% of the output is redistributed to non-crab-producing regions via interregional food trade, posing risks to the population on a national scale. The daily intake of MeHg from crabs could easily exceed the reference dose (0.1 µg/kg of body weight per day) suggested by the United States Environmental Protection Agency with consideration of coexposure from fish, rice, and other food sources. We suggest that future MeHg exposure analysis includes crab MeHg as a coexposure pathway to estimate the dietary MeHg limit accurately and emphasize the influence of interregional food trade on MeHg exposure.

Low-dose methylmercury exposure impairs the locomotor activity of zebrafish: Role of intestinal inositol metabolism

Methylmercury (MeHg) is a ubiquitous environmental toxicant with neurotoxic effects. Although its neurotoxicity had been more studied, the role of gut microbiota remains unclear. In this study, adult zebrafish and larvae were exposed to MeHgCl at the dose of 0, 1 and 10 ng/mL. MeHgCl exposure impaired the locomotor activity via upregulation of apoptosis and autophagy related genes in the brain. Intestinal and cerebral metabolome indicated that phosphatidylinositol signaling system and inositol phosphate metabolism pathways were significantly impacted in adult zebrafish upon MeHgCl exposure. The levels of myo-inositol (MI) in the intestine and brain were decreased and positively correlated. 16 S rRNA sequencing data from adult zebrafish showed that MeHgCl exposure also shifted the structure of gut microbiota and reduced the relative abundance of Bacteroidetes and Proteobacteria, which were further identified at genus level as Aeromonas and Cetobacterium. Further functional analysis indicated that MeHgCl disrupted inositol phosphate metabolism of gut microbiota. Notably, MI supplementation restored the impairment of locomotor activity and inhibited the upregulation of apoptosis and autophagy related genes, such as bcl-2 and atg5. Thus, this study not only revealed the key role of gut microbiota in MeHgCl-mediated neurotoxicity but also gave new insights into antagonizing its toxicity.