Large-Scale Observations Support Aboveground Vegetation as an Important Biological Mercury Sink in the Tibetan Plateau.

Mercury, a pervasive global pollutant, primarily enters the atmosphere through human activities and legacy emissions from the land and oceans. A significant portion of this mercury subsequently settles on land through vegetation uptake. Characterizing mercury storage and distribution within vegetation is essential for comprehending regional and global mercury cycles. We conducted an unprecedented large-scale aboveground vegetation mercury survey across the expansive Tibetan Plateau. We find that mosses (31.1 ± 0.5 ng/g) and cushion plants (15.2 ± 0.7 ng/g) outstood high mercury concentrations. Despite exceptionally low anthropogenic mercury emissions, mercury concentrations of all biomes exceeded at least one-third of their respective global averages. While acknowledging the role of plant physiological factors, statistical models emphasize the predominant impact of atmospheric mercury on driving variations in mercury concentrations. Our estimations indicate that aboveground vegetation on the plateau accumulates 32-12+21 Mg (interquartile range) mercury. Forests occupy the highest biomass and store 82% of mercury, while mosses, representing only 3% of the biomass, disproportionally contribute 13% to mercury storage and account for 43% (2.5-1.4+3.0 Mg/year) of annual mercury assimilation by vegetation. Additionally, our study underscores that extrapolating aboveground vegetation mercury storage from lower-altitude regions to the Tibetan Plateau can lead to substantial overestimation, inspiring further exploration in alpine ecosystems worldwide.

Bioimaging revealed contrasting organelle-specific transport of copper and zinc and implication for toxicity.

Zn and Cu are two of the essential trace elements and it is important to understand the regulation of their distribution on cellular functions. Herein, we for the first time investigated the subcellular fate and behavior of Zn and Cu in zebrafish cells through bioimaging, and demonstrated the completely different behaviors of Zn and Cu. The distribution of Zn2+ was concentration-dependent, and Zn2+ at low concentration was predominantly located in the lysosomes (76.5%). A further increase of cellular Zn2+ resulted in a spillover and more diffusive distribution, with partitioning to mitochondria and other regions. In contrast, the subcellular distribution of Cu+ was time-dependent. Upon entering the cells, Cu2+ was reduced to Cu+, which was first concentrated in the mitochondria (71.4%) followed by transportation to lysosomes (58.6%), and finally removal from the cell. With such differential transportation, Cu2+ instead of Zn2+ had a negative effect on the mitochondrial membrane potential and glutathione. Correspondingly, the pH of lysosomes was more sensitive to Zn2+ exposure and decreased with increasing internalized Zn2+, whereas it increased upon Cu2+ exposure. The responses of cellular pH showed an opposite pattern from the lysosomal pH. Lysosome was the most critical organelle in response to incoming Zn2+ by increasing its number and size, whereas Cu2+ reduced the lysosome size. Our study showed that Zn2+ and Cu2+ had completely different cellular handlings and fates with important implications for understanding of their toxicity.

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.

Real-time in vitro monitoring of the subcellular toxicity of inorganic Hg and methylmercury in zebrafish cells.

Mercury (Hg) is a prominent environmental contaminant and can cause various subcellular effects. Elucidating the different subcellular toxicities of inorganic Hg (Hg2+) and methylmercury (MeHg) is critical for understanding their overall cytotoxicity. In this study, we employed aggregation-induced emission (AIE) probes to investigate the toxicity of Hg at the subcellular level using an aquatic embryonic zebrafish fibroblast cell line ZF4 as a model. The dynamic monitoring of lysosomal pH and the mapping of pH distribution during Hg2+ or MeHg exposure were successfully realized for the first time. We found that both Hg2+ and MeHg decreased the mean lysosomal pH, but with contrasting effects and mechanisms. Hg2+ had a greater impact on lysosomal pH than MeHg at a similar intracellular concentration. In addition, Hg2+ in comparison to MeHg exposure led to an increased number of lysosomes, probably because of their different effects on autophagy. We further showed that MeHg (200 nM) exposure had an inverse effect on mitochondrial respiratory function. A high dose (1000 nM) of Hg2+ increased the amount of intracellular lipid droplets by 13%, indicating that lipid droplets may potentially play a role in Hg2+detoxification. Our study suggested that, compared with other parameters, lysosome pH was most sensitive to Hg2+ and MeHg. Therefore, lysosomal pH can be used as a potential biomarker to assess the cellular toxicity of Hg in vitro.

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.