Publications by authors named "Yuping Xiang"

10 Publications

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Decreased bioavailability of both inorganic mercury and methylmercury in anaerobic sediments by sorption on iron sulfide nanoparticles.

J Hazard Mater 2021 Sep 30;424(Pt B):127399. Epub 2021 Sep 30.

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.

Methylmercury (MeHg), derived via inorganic mercury (Hg(II)) methylation by anaerobic microorganisms, is a neurotoxic contaminant causing concern worldwide. Establishing how to reduce Hg(II) methylation and MeHg bioavailability is essential for effective control of Hg pollution. Iron sulfide nanoparticles (FeS) is a promising passivator for Hg(II) methylation. However, its effect on the fate of MeHg in aquatic systems remains poorly understood. This study investigated the effect of FeS on Hg(II) bioavailability, MeHg production and bioavailability in aquatic environments. Results demonstrated that FeS rapidly sorbed Hg(II) and MeHg, with sorption affected by pH, chloride ion and dissolved organic matter. Hg-specific biosensor analysis showed that Hg(II) sorbed onto FeS significantly reduced its bioavailability to microorganisms. Double stable isotope (Hg(II) and MeHg) addition revealed that FeS significantly inhibited MeHg production in anaerobic sediments. Furthermore, synthetic gut juice extraction suggested that FeS decrease concentrations of bioavailable MeHg and Hg(II), reducing their integration into food webs. However, the sorbed MeHg and Hg(II) in sediments can be released after FeS oxidation, potentially enhancing the risk of exposure to aquatic organisms. Overall, these findings increase our understanding of Hg transformation and exposure risks in aquatic systems, providing valuable information for the development of in situ Hg remediation systems.
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http://dx.doi.org/10.1016/j.jhazmat.2021.127399DOI Listing
September 2021

The efficiencies of inorganic mercury bio-methylation by aerobic bacteria under different oxygen concentrations.

Ecotoxicol Environ Saf 2021 Jan 4;207:111538. Epub 2020 Nov 4.

College of Resources and Environment, Southwest University, Chongqing 400715, China; Biological Science Research Center of Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400715, China. Electronic address:

Limited information is available about the bio-methylation of inorganic mercury (iHg) under aerobic conditions. In this study, two γ-proteobacteria strains (P. fluorescens TGR-B2 and P. putida TGR-B4) were obtained from the soil of The Three Gorges Reservoir (TGR), demonstrating effective aerobic transformation capacities of iHg into methylmercury (MeHg). Based on periodical changes in soil oxygen content of the TGR, a culture system was established, in which 300 ng Hg (II) L and O were set at 7%, 14%, and 21%, respectively. Results indicated that the two strains differed significantly in bacterial growth rate and MeHg production. The kinetic model of MeHg showed typical characteristics of a "two-staged" process: The first stage was dominated by bio-methylation, which was shown by increasing of net MeHg content. Moreover, the second stage was dominated by bio-demethylation, which decreased net MeHg content. Thus, we hypothesized that the mechanism of aerobic bacterial iHg bio-methylation: (1) should inefficiency compared to anaerobic bacteria i.e.SRB, which were regulated by hgcA/B gene clusters, (2) might be regarded as a passive stress response and depended on the bacterial iHg intoxication threshold and MeHg tolerance threshold.
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http://dx.doi.org/10.1016/j.ecoenv.2020.111538DOI Listing
January 2021

Periphyton as an important source of methylmercury in Everglades water and food web.

J Hazard Mater 2021 05 12;410:124551. Epub 2020 Nov 12.

Department of Chemistry & Biochemistry and Southeast Environmental Research Center, Florida International University, 11200 SW 8th ST, Miami, FL 33199, USA; Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Electronic address:

Periphyton is ubiquitous in Florida Everglades and has a profound effect on mercury (Hg) cycling. Enhanced methylmercury (MeHg) production in periphyton has been well documented, but the re-distribution of MeHg from periphyton remains unknown. In this study, periphyton, sediments, surface water, periphyton overlying water, and periphyton porewater were collected from Everglades for analyzing the distribution of MeHg and total Hg (THg). Results showed that there were no significant differences in THg and MeHg in different types of periphyton, but they all displayed higher MeHg levels than sediments. MeHg distribution coefficients (logk) in periphyton were lower than in sediments, suggesting that periphyton MeHg could be more labile entering aquatic cycling and bioaccumulation. In water, the more the distance of water samples taken from periphyton, the lower the MeHg and dissolved organic carbon concentrations were detected. In extracellular polymeric substances of periphyton, MeHg in colloidal fractions was significantly higher than that in capsular fractions. It was estimated that approximately 10% (or 1.35 kg) of periphyton MeHg were passed on to mosquitofish entering the food web during wet season, contributing 73% of total Hg stocked in mosquitofish. These results revealed the importance of periphyton on water MeHg distribution and MeHg bioaccumulation in Everglades.
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http://dx.doi.org/10.1016/j.jhazmat.2020.124551DOI Listing
May 2021

Mercury transport, transformation and mass balance on a perspective of hydrological processes in a subtropical forest of China.

Environ Pollut 2019 Nov 20;254(Pt B):113065. Epub 2019 Aug 20.

College of Resources and Environment, Southwest University, Chongqing, 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400715, China. Electronic address:

Forest ecosystem has long been suggested as a vital component in the global mercury (Hg) biogeochemical cycling. However, there remains large uncertainties in understanding total Hg (THg) and methylmercury (MeHg) variations and their controlling factors during the whole hydrological processes in forest ecosystems. Here, we quantified Hg mass flow along hydrological processes of wet deposition, throughfall, stemflow, litter leachate, soil leachate, surface runoff, and stream, and litterfall Hg deposition, and air-forest floor elemental Hg (Hg) exchange flux to set up a Hg mass balance in a subtropical forest of China. Results showed that THg concentration in stream was lower than that in wet deposition, while an opposite characteristic for MeHg concentration, and both THg and MeHg fluxes of stream were lower than those of wet deposition. Variations of THg and MeHg in throughfall and litter leachate had strong direct and indirect effects on controlling variations of THg and MeHg in surface runoff, soil leachate and stream, respectively. Especially, the net Hg methylation was suggested in the forest canopy and forest floor layers, and significant particulate bound Hg (PBM) filtration was observed in soil layers. The Hg mass balance showed that the litterfall Hg deposition was the main Hg input for forest floor Hg, and the elemental Hg vapor (Hg) re-emission from forest floor was the dominant Hg output. Overall, we estimated the net THg input flux of 13.8 μg m yr and net MeHg input flux of 0.6 μg m yr within the forest ecosystem. Our results highlighted the important roles of forest canopy and forest floor to shape Hg in output flow, and the forest floor is a distinct sink of MeHg.
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http://dx.doi.org/10.1016/j.envpol.2019.113065DOI Listing
November 2019

Production and migration of methylmercury in water-level-fluctuating zone of the Three Gorges Reservoir, China: Dual roles of flooding-tolerant perennial herb.

J Hazard Mater 2020 01 9;381:120962. Epub 2019 Aug 9.

College of Resources and Environment, Southwest University, Chongqing 400715, China. Electronic address:

Water-level-fluctuating zone (WLFZ) is a prevalent water-land ecotone favorable for mercury (Hg) methylation. The succession of flooding tolerance plants in WLFZ gradually changes the landscape, and also brings a new question worth understanding whether these plants would enhance methylmercury (MeHg) production in WLFZ and increase risks to the aquatic environment. Given bermudagrass (Cynodon dactylon (L). Pers) as the dominant perennial herb with high flooding-tolerance in WLFZ of the Three Gorges Reservoir (TGR), we conducted a comprehensive study to investigate its roles in the production and migration of MeHg in WLFZ by field observations and stable isotope tracer experiments. Results showed that both elevated MeHg levels and Hg methylation rates appeared in soil/sediment in bermudagrass growing area, implying that the growth of bermudagrass could significantly enhance MeHg production. However, MeHg migration from sediment to water was restricted during the flooding period of the TGR, as obviously higher partitioning coefficients of MeHg between the sediment and porewater (p <  0.05) and lower MeHg release fluxes were observed in vegetated area, indicating that the presence of bermudagrass instead probably decreased the water MeHg level. Whereas, it is noteworthy that elevated MeHg in soil/sediment induced by the bermudagrass could pose potential risks to the benthos and further to the TGR food chain.
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http://dx.doi.org/10.1016/j.jhazmat.2019.120962DOI Listing
January 2020

The Draft Genome Sequence of Pseudomonas putida Strain TGRB4, an Aerobic Bacterium Capable of Producing Methylmercury.

Curr Microbiol 2020 Apr 19;77(4):522-527. Epub 2019 Apr 19.

College of Resources and Environment, Southwest University, Chongqing, 400715, China.

Mercury (Hg) methylation is mainly a microbial process mediated by anaerobes. The continued study of Pseudomonas putida (P. putida) strain TGRB4 genome was inspired by the fact that it can transform Hg into the highly toxic methylmercury (MeHg) under aerobic conditions. P. putida strain TGRB4 is a Gram-negative rod-shaped Gamma-proteobacterium (γ-proteobacterium), isolated from the soil in a typical water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR), which suffered from seasonally water level alternations every year. Draft genome assembly of P. putida strain TGRB4 is presented here, which was sequenced using Illumina Hiseq and PacBio single-molecule real-time (SMRT) platforms. Its genome harbors a total of 5504 genes and a G + C content of 62.6%. We further identified the enzymes related to Hg methylation, and found two well-known methyltransferase, including 5-methyl-tetrahydrofolate (5-methyl-THF) and S-adenosylmethionine (AdoMet), were annotated in the genome of P. putida strain TGRB4. This genome information could be treated as a research material to further study the Hg methylation mechanisms under aerobic environment.
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http://dx.doi.org/10.1007/s00284-019-01670-3DOI Listing
April 2020

A Review of Studies on the Biogeochemical Behaviors of Mercury in the Three Gorges Reservoir, China.

Bull Environ Contam Toxicol 2019 May 11;102(5):686-694. Epub 2019 Mar 11.

College of Resources and Environment, Southwest University, Chongqing, 400715, China.

The Three Gorges Reservoir (TGR) is a relatively large reservoir, and its water level management actions produce a widespread water level fluctuation zone (WLFZ), which has characteristics of both terrestrial and aquatic ecosystems. Here, an integrated overview of current knowledge on Hg behaviors in the TGR, especially the WLFZ, as well as exposure risk to local residents was presented. Hg levels in the TGR were comparable with other natural aquatic systems. WLFZ in the TGR was confirmed to be an environment favorable for Hg methylation by enhancing microbial activity, promoting sulfur cycling and increasing the level of low-molecular-weight organic matters. However, elevated fish Hg concentrations did not follow the impoundment of TGR, indicating no obvious reservoir effect, while it is still noteworthy that frequently consuming fish is likely to be a methylmercury (MeHg) exposure pathway for specific populations e.g. fishermen around the TGR.
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http://dx.doi.org/10.1007/s00128-019-02586-1DOI Listing
May 2019

Water level fluctuations influence microbial communities and mercury methylation in soils in the Three Gorges Reservoir, China.

J Environ Sci (China) 2018 Jun 17;68:206-217. Epub 2018 Mar 17.

College of Resources and Environment, Southwest University, Chongqing 400715, China; Chongqing Engineering Research Center for Agricultural Non-point Source Pollution Control in the Three Gorges Reservoir Area, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400715, China. Electronic address:

Reservoirs tend to have enhanced methylmercury (MeHg) concentrations compared to natural lakes and rivers, and water level fluctuations can promote MeHg production. Until now, little research has been conducted on the effects of microorganisms in soils for the formation of MeHg during different drying and flooding alternating conditions in the Three Gorges Reservoir (TGR). This study aimed to understand how water level fluctuations affect soil microbial composition and mercury concentrations, and if such microbial variations are related to Hg methylation. The results showed that MeHg concentrations and the ratios of MeHg to THg (MeHg%) in soils were higher in the seasonally drying and flooding alternating areas (DFAs, 175-155m) than those in the non-inundated (NIAs, >175m) and inundated areas (IAs, <145m). However, MeHg% in all samples was less than 1%, indicating that the Hg methylation activity in the soils of the TGR was under a low level. 454 high-throughput sequencing of 16S rRNA gene amplicons showed that soil bacterial abundance and diversity were relatively higher in DFA compared to those in NIA and IA, and microbial community composition varied in these three areas. At the family level, those groups in Deltaproteobacteria and Methanomicrobia that might have many Hg methylators were also showed a higher relative abundance in DFA, which might be the reason for the higher MeHg production in these areas. Overall, our results suggested that seasonally water level fluctuations can enhance the microbial abundance and diversity, as well as MeHg production in the TGR.
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http://dx.doi.org/10.1016/j.jes.2018.03.009DOI Listing
June 2018

Methylmercury production in soil in the water-level-fluctuating zone of the Three Gorges Reservoir, China: The key role of low-molecular-weight organic acids.

Environ Pollut 2018 Apr 4;235:186-196. Epub 2018 Jan 4.

College of Resources and Environment, Southwest University, Chongqing 400715, China; Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing 400715, China. Electronic address:

As important parts of dissolved organic matter, low-molecular-weight organic acids (LMWOAs) typically play important roles in desorbing Hg(II) from the soil solid-phase, which may directly or indirectly impact methylmercury (MeHg) production. However, the mechanism of these processes remains unclear. To better understand the effects of LMWOAs on Hg methylation in the soil, a field study was conducted to investigate the distribution of LMWOAs and their relationship with soil MeHg in a seasonally inundated area in the Three Gorges Reservoir (TGR), China. Meanwhile, laboratory simulation experiments were performed to determine the potential mechanism of LMWOAs in Hg methylation. The field investigation detected considerable amounts of LMWOAs in soil, among which tartaric acid and oxalic acid were dominant components. Among which, tartaric acid and oxalic acid were dominant components. Also, a seasonally and spatially heterogeneous distribution of LMWOAs in soil was observed. Notably, a significant positive relationship was found between MeHg concentrations and LMWOA pools in soil (r = 0.969, p < .01), implying that LMWOAs could promote soil MeHg production. The simulation experiments confirmed that the MeHg levels in soil were largely elevated with the addition of LMWOAs, which occurred mainly in oxygen-deficient environment and was mediated by biotic factors. The soluble Hg-LMWOA complexes, which were formed by the enhanced desorption of Hg(II) from solid-phase, were mostly responsible for the elevated MeHg production in soil. Moreover, those LMWOAs with more carboxylic groups were believed to enhance the net production of MeHg. The generated MeHg in sediment could diffuse into the overlying water, which thus poses a potential threat to the aquatic food web. Therefore, the enhanced Hg methylation caused by LMWOAs should be given more attention, especially in a seasonally inundated ecosystem, where the MeHg exposure is usually related to fishery activities.
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http://dx.doi.org/10.1016/j.envpol.2017.12.072DOI Listing
April 2018

[Acupoint plaster therapy with midnight-noon ebb-flow hour-prescription method for senile osteoporosis:a randomized controlled trial].

Zhongguo Zhen Jiu 2017 Apr;37(4):349-354

College of Nursing, Chengdu University of TCM, Chengdu 611137, Sichuan Province, China.

Objective: To compare the clinical efficacy differences between acupoint plaster therapy with midnight-noon ebb-flow hour-prescription method and traditional acupoint plaster therapy for senile osteoporosis (SOP).

Methods: With randomized controlled blind design, 76 SOP patients with deficiency of liver and kidney syndrome were randomly divided into an observation group and a control group, 38 cases in each one. Based on oral administration of caltrate D, the patients in the observation group were treated with acupoint plaster therapy with midnight-noon ebb-flow hour-prescription method at Yingu (KI 10), Taixi (KI 3), Dazhong (KI 4), Fuliu (KI 7) and Zhiyin (BL 67), while the patients in the control group were treated with traditional acupoint plaster therapy. Each plaster therapy lasted for 6 h, once a day; there was an interval of 2 d after consecutive 5-day treatment; 4 weeks were taken as one course, and totally 2 courses were given. Visual analogue scale (VAS) and Oswestry Disability Index (ODI) were used to evaluate the pain and dysfunction before intervention, after 4 weeks and 8 weeks intervention. Osteoporosis symptom rating sale and quality of life questionnaire of the European foundation for Osteoporosis (QUALEFFO-41) were adopted to evaluate the TCM syndrome and quality of life before and after 8-week intervention.

Results: All the outcomes were significantly improved after treatment in the two groups (<0.01,<0.05); after 4 weeks and 8 weeks of treatment, the VAS and ODI in the observation group were lower than those in the control group (all <0.05). Repeated ANOVA indicated the VAS and ODI were significant in group effect, time effect and interaction effect (all <0.01). Further comparison showed that VAS and ODI at later time points were lower than those in the early time points (all <0.01). After the treatment, the scores of TCM syndrome and QUALEFFO-41 in the observation group were lower than those in the control group (all <0.05). The effective rate was 85.7% (30/35) in the observation group, which was superior to the effective rate in the control group[74.3%(26/35), <0.05].

Conclusions: The acupoint plaster therapy with midnight-noon ebb-flow hour-prescription method is superior to traditional acupoint plaster therapy in improving pain, dysfunction, TCM syndrome and quality of life in SOP patients; in addition, its clinical efficacy is significant.
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http://dx.doi.org/10.13703/j.0255-2930.2017.04.002DOI Listing
April 2017
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