https://cyberleninka.org/article/n/205972.pdf

Globally enhanced mercury deposition during the end-Pliensbachian extinction and Toarcian OAE: A link to the Karoo–Ferrar Large Igneous Province

China's rapid economic growth has been accompanied by increasing environmental pollution. Mangrove ecosystems are now facing greater pollution pressures due to elevated chemical discharges from various land-based sources. Data on the levels of heavy metals and organic pollutants in mangrove compartments (sediments, plants, zoobenthos, and fish) in China over the past 20 years have been summarized to evaluate the current pollution status of the mangrove ecosystem. Overall, the Pearl River and Jiulong River estuaries were severely polluted spots. Concentrations of Cu, Zn, Cd, and Pb in mangrove sediments of Guangdong, Fujian, and Hong Kong were higher than those from Guangxi and Hainan. The pollution status was closely linked to industrialization and urbanization. The highest concentrations of polycyclic aromatic hydrocarbons (PAHs) were found in mangrove sediments from Hong Kong, followed by Fujian and Guangdong. Mangrove plants tend to have low-enriched ability for heavy metals and organic pollutants. Much higher levels of Pb, Cd, and Hg were observed in mollusks.

Heavy metal and organic contaminants in mangrove ecosystems of China: a review

. An automated biogeochemical microcosm system allowing controlled variation of redox potential (EH) in soil suspensions was used to assess the effect of various factors on the mobility of mercury (Hg) as well as on the methylation of Hg in two contaminated floodplain soils with different Hg concentrations (approximately 5 mg Hg kg−1 and >30 mg Hg kg–1). The experiment was conducted under stepwise variation from reducing (approximately −350 mV at pH 5) to oxidizing conditions (approximately 600 mV at pH 5). Results of phospholipid fatty acids (PLFA) analysis indicate the occurrence of sulfate reducing bacteria (SRB) such as Desulfobacter species (10Me16:0, cy17:0, 10Me18:0, cy19:0) or Desulfovibrio species (18:2ω6,9), which are considered to promote Hg methylation. The products of the methylation process are lipophilic, highly toxic methyl mercury species such as the monomethyl mercury ion [MeHg+], which is named as MeHg here. The ln(MeHg/Hgt) ratio is assumed to reflect the net production of monomethyl mercury normalized to total dissolved Hg (Hgt) concentration. This ratio increases with rising dissolved organic carbon (DOC) to Hgt ratio (ln(DOC/Hgt) ratio) (R2 = 0.39, p

/pdf/biogeochemical-factors-affecting-mercury-methylation-rate-in-a5a865dbxx.pdf

Biogeochemical factors affecting mercury methylation rate in two contaminated floodplain soils

Mercury is a global pollutant that can be transported over long distances and can bioaccumulate. Currently, China is the country that contributes most to atmospheric Hg emissions and has the greatest intentional (industrial) use of Hg. Mercury in the Chinese environment is generally elevated, particularly in air and water bodies. Remote areas in China also show elevated Hg levels in air and water bodies compared to other rural regions in the world. Large river estuaries are often heavily affected by upstream industrial sources. Mercury is also elevated in sediments, a direct result of contamination in river systems. Regardless of the few heavily polluted sites, the urban environment in Chinese cities is comparable to that of other megacities in terms of Hg pollution, considering the size and rapid development of Chinese cities. Studies on Hg in fish showed generally low levels of contamination resulting from low bioaccumulation of Hg in the mostly short food chains. Mercury in rice has recently received increased research interest; elevated concentrations have been reported from rice grown in contaminated areas and may pose a threat to people dependent on such locally grown food. For the general population, Hg exposure from rice is, however, small. In addition, Hg hair concentration in the Chinese population showed generally low levels of exposure to Hg, except for people with special occupational exposure. Environ. Toxicol. Chem. 2012; 31: 2431–2444. © 2012 SETAC

https://setac.onlinelibrary.wiley.com/doi/pdf/10.1002/etc.1980

Environmental mercury in China: A review

Distribution and ecological risk assessment of heavy metals in surface sediments of a typical restored mangrove-aquaculture wetland in Shenzhen, China

Estuaries are important sites for mercury (Hg) methylation, with sulfate-reducing bacteria (SRB) thought to be the main Hg methylators. Distributions of total mercury (THg) and methylmercury (MeHg) in mangrove sediment and sediment core from Jiulong River Estuary Provincial Mangrove Reserve, China were determined and the possible mechanisms of Hg methylation and their controlling factors in mangrove sediments were investigated. Microbiological and geochemical parameters were also determined. Results showed that SRB constitute a small fraction of total bacteria (TB) in both surface sediments and the profile of sediments. The content of THg, MeHg, TB, and SRB were (350 +/- 150) ng/g, (0.47 +/- 0.11) ng/g, (1.4 x10(11) +/- 4.1 x 10(9)) cfu/g dry weight (dw), and (5.0 x 10(6) +/- 2.7 x 10(6)) cfu/g dw in surficial sediments, respectively, and (240 +/- 24) ng/g, (0.30 +/- 0.15) ng/g, (1.9 x 10(11) +/- 4.2 x 10(10)) cfu/g dw, and (1.3 x 10(6) +/- 2.0 x 10(6)) cfu/g dw in sediment core, respectively. Results showed that THg, MeHg, TB, MeHg/THg, salinity and total sulfur (TS) increased with depth, but total organic matter (TOM), SRB, and pH decreased with depth. Concentrations of MeHg in sediments showed significant positive correlation with THg, salinity, TS, and MeHg/THg, and significant negative correlation with SRB, TOM, and pH. It was concluded that other microbes, rather than SRB, may also act as main Hg methylators in mangrove sediments.

Methylmercury and sulfate-reducing bacteria in mangrove sediments from Jiulong River Estuary, China.

Plant is an important role in biogeochemical cycle of Hg. The aim of this study is to ascertain Hg accumulation in several kinds of mangrove plants, and to discuss relationship among Hg concentrations in mangrove plants and different Hg speciation in sediments. Contents of total mercury (THg) in mangrove plants and sediments were determined. Hg speciation was determined with a modified Tessier's method. Contents of THg of the mangrove plants were in the range of 817.5-3 197.6 ng/g. In detail, Hg concentration was (1 579.4 +/- 1 326.8) ng/g in Kandelia candel, (2 115.1 +/- 1 892.3) ng/g in Aegiceras corniculatum, (2 159.3 +/- 1 678.7) ng/g in Avicennia marina, (2 566.5 +/- 821.6) ng/g in Bruguiera gymnorrhiza, (2 104.3 +/- 1 661.8) ng/g in Excoecaria agallocha, (3 197.6 +/- 2 782.8) ng/g in Sonneratia apetala, (817.5 +/- 632.3) ng/g in Acanthus ilicifolius, (1 801.8 +/- 1 255.4) ng/g in Rhizophora. stylosa, respectively. There are obvious interspecific variation, and organic variation in THg contents of mangrove plants, which is closely related to environment and physiological characteristics of mangrove plants. Enrichment of THg in mangrove plants was inhomogeneous, following the order of Sonneratia apetala > Bruguiera gymnorrhiza > Avicennia marina > Aegiceras corniculatum > Excoecaria agallocha > Rhizophora stylosa > Kandelia candel > Acanthus ilicifolius. Mercury exists mainly in volatile form in most mangrove wetlands, but mainly in the form of residue in sediments from Shenzhen mangrove wetlands. Significantly positive correlations were found among Hg concentrations in leaves and stems of Sonneratia apetala and volatile Hg, exchangeable Hg of sediments. Significantly positive correlations were also found among Hg concentrations in leaves of Excoecaria agallocha and volatile Hg, exchangeable Hg of sediments. But, there is no significant correlation between Hg concentrations of most mangrove plants and different Hg speciation in sediments. It showed that plants assimilate Hg from different sources, such as water, sediment and air, and that Hg assimilated by plants could transfer among different plant organics.

Distribution of Hg in mangrove plants and correlation with Hg speciation in sediments

Surficial sediment samples were collected from main mangrove wetlands of China, mercury, pH, salinity, organic matters, grain size, Fe/Hg, Mn/Hg were analyzed. Mercury content ranges from 2.3 to 903.6 ng x g(-1), with a average of (197 +/- 137.6) ng x g(-1). Compared with local background level, serious Hg pollution with high Hg content was found in 7 areas, including Luoyangqiao [(467.5 +/- 68.8) ng x g(-1)], Fugong [(438.2 +/- 147.0) ng x g(-1)], Ewan [(264.3 +/- 89.2) ng x g(-1)], Yaojiayu [(125.4 +/- 27.1) ng x g(-1)], Fujian Province; Sanya [(164.8 +/- 143.9) ng x g(-1)], Dongzhaigang [(314.1 +/- 335.7) ng x g(-1)], Hainan Province, Shenzhen [(179.9 +/- 7.7) ng x g(-1)], Guangdong Province. Hg content was similar with background value in the other 6 areas, including Yunxiao [(63.3 +/- 43.9)ng x g(-1)], Fujian Province; Gaoqiao [(178.6 +/- 127.0) ng x g(-1)], Guangdong Province; Daguansha [(26.1 +/- 18.8) ng x g(-1)], Shankou [(73.8 +/- 21.1) ng x g(-1)], Beilun estuary [(117.8 +/- 51.4) ng x g(-1)], Qinzhou Bay [(147.5 +/- 107.6) ng x g(-1)], Guangxi Autonomous Region. Discrepancy of total Hg concentrations in mangrove wetlands is due to many environmental factors and human activities. Parameters such as grain size, pH, organic matter, Fe/Hg, Mn/Hg are significantly correlated with total Hg respectively. Clay and Fe/Hg are obvious factors influencing total Hg concentration. Impact of environmental factors on mercury can be showed by regression equation.

Hui-na Lin

Papers

Methylmercury and sulfate-reducing bacteria in mangrove sediments from Jiulong River Estuary, China.

Distribution of Hg in mangrove plants and correlation with Hg speciation in sediments

Distribution of mercury in surficial sediments from main mangrove wetlands of China