Mei Meng

Accumulation of total mercury and methylmercury in rice plants collected from different mining areas in China

A total of 155 rice plants were collected from ten mining areas in three provinces of China (Hunan, Guizhou and Guangdong), where most of mercury (Hg) mining takes place in China. During the harvest season, whole rice plants were sampled and divided into root, stalk & leaf, husk and seed (brown rice), together with soil from root zone. Although the degree of Hg contamination varied significantly among different mining areas, rice seed showed the highest ability for methylmercury (MeHg) accumulation. Both concentrations of total mercury (THg) and MeHg in rice plants were significantly correlated with Hg levels in soil, indicating soil is still an important source for both inorganic mercury (IHg) and MeHg in rice plants. The obvious discrepancy between the distribution patterns of THg and MeHg reflected different pathways of IHg and MeHg accumulation. Water soluble Hg may play more important role in MeHg accumulation in rice plants.

Growing Rice Aerobically Markedly Decreases Mercury Accumulation by Reducing Both Hg Bioavailability and the Production of MeHg

Rice consumption represents a major route of mercury (Hg) and methylmercury (MeHg) exposure for those living in certain areas of inland China. In this study we investigated the effects of water management on bioavailable Hg, MeHg, and sulfate-reducing bacteria (SRB, abundance and community composition) in rhizosphere soil, and total Hg (THg) and MeHg in rice plants grown under glasshouse and paddy field conditions. Aerobic conditions greatly decreased the amount of THg and MeHg taken up by rice plants and affected their distribution in different plant tissues. There were positive correlations between bioavailable Hg and THg in brown rice and roots and between numbers of SRB and MeHg in brown rice, roots, and rhizosphere soil. Furthermore, the community composition of SRB was dramatically influenced by the water management regimes. Our results demonstrate that the greatly reduced bioavailability of Hg and production of MeHg are due to decreased SRB numbers and proportion of Hg methylators in the rhizosphere under aerobic conditions. These are the main reasons for the reduced Hg and MeHg accumulation in aerobically grown rice. Water management is indicated as an effective measure that can be used to reduce Hg and MeHg uptake by rice plants from Hg-contaminated paddy fields.

Variations and constancy of mercury and methylmercury accumulation in rice grown at contaminated paddy field sites in three Provinces of China

Many paddy fields have been contaminated by mercury (Hg) in mining areas of China. In this study, twenty-six rice cultivars and three Hg contaminated paddy fields in different geographic regions were selected for field trials and aimed to investigate the variations and similarities in total Hg (THg) and methylmercury (MeHg) accumulations in brown rice (seeds) across sites. Our results revealed widescale cultivar variation in THg (13-52 ng g(-1) at Wanshan) and MeHg (3.5-23 ng g(-1)) accumulation and %MeHg (17.7-89%) in seeds. The ability to translocate is an important factor in the levels of THg and MeHg in seed. Cultivar tended to stability in THg accumulation across sites. Some cultivars accumulated lower concentrations of both THg and MeHg in seeds at fields seriously contaminated by Hg. Present results suggest that appropriate cultivar selection is a possible way to reduce THg and MeHg accumulation in seeds of rice grown in Hg-contaminated regions.

Radial oxygen loss has different effects on the accumulation of total mercury and methylmercury in rice

Background and AimsMercury (Hg) pollution in paddy fields and rice has aroused great concern in recent years. This study investigated the dynamic changes of radial oxygen loss (ROL) and Fe plaque formation on roots, and their effects on Hg accumulation in rice plants.MethodsA rhizobag experiment was conducted to study temporal variations and correlations between ROL (amounts and rates), Fe plaque formation, total Hg (THg) and methylmercury (MeHg) in plant tissues and in plaque of four rice cultivars during six growth stages.ResultsROL amounts and Fe plaque formation increased from tillering to reproductive stages, then ROL amounts gradually decreased until maturation stage, whereas Fe plaque remained relatively stable. ROL rates continued to decline during the entire growth period. Both ROL amounts and Fe concentrations in plaque were positively correlated with THg concentrations in the plaque, whereas negatively correlated with THg in straw and brown rice. However, there were no significant relationships between ROL, Fe in plaque and MeHg in plaque and in plant tissues.ConclusionsROL has great effects on THg but not MeHg accumulation in rice plants. Rice cultivars with higher ROLs tend to have a greater ability to reduce THg accumulation in brown rice.

Chlorinated Polyfluoroalkyl Ether Sulfonic Acids in Marine Organisms from Bohai Sea, China: Occurrence, Temporal Variations, and Trophic Transfer Behavior

F-53B, the commercial product of chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs), has been used in Chinese chrome plating industry for 30 years, and was recently identified in the environment, which caused great concerns. So far, limited investigations have been performed on their environmental occurrence, fate and impact. In this study, we demonstrated the wide occurrence of Cl-PFESAs and their trophic transfer behavior in marine organisms from Chinese Bohai Sea. 6:2 Cl-PFESA (<0.016-0.575 ng/g wet weight) was the dominant congener, and 8:2 Cl-PFESA (<0.022-0.040 ng/g) was occasionally detected. Compared to other perfluoroalkyl and polyfluoroalkyl substances (PFASs) of concern, the levels of Cl-PFESAs were relatively lower in marine organisms. Based on the comparative analysis of Cl-PFESA contamination in mollusk samples collected in 2010-2014, both the concentrations and detection frequencies of Cl-PFESAs tended to increase in this region. And this kind of chemicals were more vulnerable to be accumulated in marine organisms at relatively higher trophic levels. Similar to perfluorooctanesulfonate (PFOS) and the long chain perfluorinated carboxylates (PFCAs), 6:2 Cl-PFESA could be magnified along the food chain. Accordingly, the potential threat might be posed to the wildlife and human beings due to unintended exposure to Cl-PFESAs.

Spatial distribution and fate of perfluoroalkyl substances in sediments from the Pearl River Estuary, South China

In this study, 54 sediment samples were collected from the Pearl River Estuary (PRE) in Southern China to study the spatial distribution and patterns of PFASs in this region. PFAS concentrations in the sediment samples ranged from nd (below detection limit) to 2.41 ng g(-1) dw (dry weight) with an average value of 0.79 ng g(-1) dw. PFAS concentrations were higher at the nearshore sampling sites than in the others. Perfluorobutanesulfonate (PFBS) and perfluorohexanesulfonate (PFHxS) were the two dominant compounds among the target PFASs, which may be due to their production and use as PFOS substitutes in the Pearl River Delta (PRD) areas. Significant linear relationships were found between total PFAS concentrations and total organic carbon (TOC) (R=0.30, p<0.05). The preliminary environmental risk assessment indicated that PFOS and PFOA in the regional sediments posed no significant ecological risk to the benthic organisms at present levels.

Distribution of mercury in coastal marine sediments of China: Sources and transport

A total of 220 surface sediments and eight sediment cores were analyzed to study the distribution and transport of Hg in Chinese marginal seas. Spatial distribution showed a general offshore decreasing trend towards the outer continental shelf. Vertical profiles of sediment cores displayed a general increasing trend from bottom to surface layers. Coastal land-based discharges and river-derived inputs are probably the main sources of Hg in coastal sediments of China seas, while TOC, pH, ocean currents and sediment characteristics could play important roles in the transport and spatial distribution of Hg in sediment. The influence of TOC on Hg concentration is more significant than that of pH. The mud deposits on the coastal shelves are main sinks of Hg in the region. The results showed that sedimentary Hg was affected by regional anthropogenic activities and riverine runoffs, and was also influenced by long-range atmospheric transport and ocean current circulations.

Biomagnification of mercury in mollusks from coastal areas of the Chinese Bohai Sea

The multiple recognized mollusk species are usually regarded as one group lying at the second trophic level in the marine ecosystem. As a result, the virtual resolution of Hg uptake and transfer processes that occur in different mollusks would be overlooked. In this work, the concentrations of total mercury (THg) and methylmercury (MeHg), δ15N, δ13C and lipid contents were comprehensively analyzed in 11 mollusk species collected from the Chinese Bohai Sea during 2007–2012. The contents of THg and MeHg were in the range 27.2–461.1 and 2.1–295.5 μg kg−1, respectively. The trophic levels (TLs) were in the range 1.99–4.02. The biomagnification of Hg was evident from the significant positive correlations between Hg contents and TLs, and from the trophic magnification factors (TMFs). MeHg is the main species of Hg magnification in mollusks, while growth dilution occurs in the trophic transfer of inorganic mercury (IHg). TLs showed a greater effect on Hg levels in mollusks than lipid contents.