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

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

Mangroves are under increasing heavy metal (HM) pollution pressure from human activities because of the rapid industrialization and urbanization in coastal areas. Field and laboratory experiments showed that the tolerance of mangrove plants to HM stress is normally a mixture of metal avoidance and scavenging of reactive oxygen species (ROS). In this review, related studies during the past few decades on the accumulation and tolerance of mangrove to HMs have been synthesized. In mangroves, metal accumulation mainly occurred at the root level with restricted transport to the aerial portions of the plant. The common founded HMs, such as copper, zinc, cadmium, chromium, and mercury, generally showed high bioconcentration factor in roots, while the concentration factors for these metals in leaves were usually much lower than one. The limited translocation of the toxic metals to the aerial parts renders the mangrove plants a high endurance ability to high levels of HM stress. To protect the cellular components from oxidative damage by HMs, mangroves have developed both enzymatic and nonenzymatic antioxidant mechanisms to scavenge the ROS. In some circumstances, the changes of antioxidative enzyme activity were usually in accordance with the changes of toxic metal concentrations in plant tissues. However, the responses of antioxidative enzymes in mangroves to HM stress varied with plant species, metal type, and concentration, as well as the duration of the treatment time. More toxicity tests are needed with early life stages of mangroves to determine threshold effect concentrations under more realistic conditions.

Accumulation and Tolerance of Mangroves to Heavy Metals: a Review

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.

Zhen-zhen Hu

Papers

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