Jiating Zhao

Selenium inhibits the phytotoxicity of mercury in garlic (Allium sativum)

To investigate the influence of selenium on mercury phytotoxicity, the levels of selenium and mercury were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) in garlic tissues upon exposure to different dosages of inorganic mercury (Hg(2+)) and selenite (SeO3(2-)) or selenate (SeO4(2-)). The distributions of selenium and mercury were examined with micro-synchrotron radiation X-ray fluorescence (μ-SRXRF), and the mercury speciation was investigated with micro-X-ray absorption near edge structure (μ-XANES). The results show that Se at higher exposure levels (>1mg/L of SeO3(2-) or SeO4(2-)) would significantly inhibit the absorption and transportation of Hg when Hg(2+) levels are higher than 1mg/L in culture media. SeO3(2-) and SeO4(2-) were found to be equally effective in reducing Hg accumulation in garlic. The inhibition of Hg uptake by Se correlates well with the influence of Se on Hg phytotoxicity as indicated by the growth inhibition factor. Elemental imaging using μ-SRXRF also shows that Se could inhibit the accumulation and translocation of Hg in garlic. μ-XANES analysis shows that Hg is mainly present in the forms of Hg-S bonding as Hg(GSH)2 and Hg(Met)2. Se exposure elicited decrease of Hg-S bonding in the form of Hg(GSH)2, together with Se-mediated alteration of Hg absorption, transportation and accumulation, may account for attenuated Hg phytotoxicity by Se in garlic.

Mercury modulates selenium activity via altering its accumulation and speciation in garlic (Allium sativum)

Combined pollution of selenium (Se) and mercury (Hg) has been known in Wanshan district (Guizhou Province, China). A better understanding of how Se and Hg interact in plants and the phytotoxicity thereof will provide clues about how to avoid or mitigate adverse effects of Se/Hg on local agriculture. In this study, the biological activity of Se has been investigated in garlic with or without Hg exposure. Se alone can promote garlic growth at low levels (<0.1 mg L(-1)), whereas it inhibits garlic growth at high levels (>1 mg L(-1)). The promotive effect of Se in garlic can be enhanced by low Hg exposure (<0.1 mg L(-1)). When both Se and Hg are at high levels, there is a general antagonistic effect between these two elements in terms of phytotoxicity. Inductively coupled plasma mass spectrometry (ICP-MS) data suggest that Se is mainly concentrated in garlic roots, compared to the leaves and the bulbs. Se uptake by garlic in low Se medium (<0.1 mg L(-1)) can be significantly enhanced as Hg exposure levels increase (P < 0.05), while it can be inhibited by Hg when Se exposure levels exceed 1 mg L(-1). The synchrotron radiation X-ray fluorescence (SRXRF) mapping further shows that Se is mainly concentrated in the stele of the roots, bulbs and the veins of the leaves, and Se accumulation in garlic can be reduced by Hg. The X-ray absorption near edge structure (XANES) study indicates that Se is mainly formed in C-Se-C form in garlic. Hg can decrease the content of inorganic Se mainly in SeO3(2-) form in garlic while increasing the content of organic Se mainly in C-Se-C form (MeSeCys and its derivatives). Hg-mediated changes in Se species along with reduced Se accumulation in garlic may account for the protective effect of Hg against Se phytotoxicity.

Mechanistic understanding of MeHg-Se antagonism in soil-rice systems: the key role of antagonism in soil.

Methylmercury (MeHg) accumulation in rice has great implications for human health. Here, effects of selenium (Se) on MeHg availability to rice are explored by growing rice under soil or foliar fertilization with Se. Results indicate that soil amendment with Se could reduce MeHg levels in soil and grain (maximally 73%). In contrast, foliar fertilization with Se enhanced plant Se levels (3–12 folds) without affecting grain MeHg concentrations. This evidence, along with the distinct distribution of MeHg and Se within the plant, demonstrate for the first time that Se-induced reduction in soil MeHg levels (i.e., MeHg-Se antagonism in soil) rather than MeHg-Se interactions within the plant might be the key process triggering the decreased grain MeHg levels under Se amendment. The reduction in soil MeHg concentrations could be mainly attributed to the formation of Hg-Se complexes (detected by TEM-EDX and XANES) and thus reduced microbial MeHg production. Moreover, selenite and selenate were equally effective in reducing soil MeHg concentrations, possibly because of rapid changes in Se speciation. The dominant role of Se-induced reduction in soil MeHg levels, which has been largely underestimated previously, together with the possible mechanisms advance our mechanistic understanding about MeHg dynamics in soil-rice systems.

Synchrotron radiation techniques for nanotoxicology

UNLABELLED Nanotoxicology studies the interactions of engineered nanomaterials with biological systems. Traditional in vitro and in vivo toxicological assays have been successfully employed. However, the toxicological mechanisms of nanoparticles might not be the same as those incurred in traditional molecular toxicology. Furthermore, how to realize in situ and real time measurements especially in the biological microenvironment is still a challenge. Synchrotron radiation, which is highly polarized and tunable, has been proved to play an indispensible role for nanotoxicology studies. In this review, the role of synchrotron radiation techniques is summarized in screening physicochemical characteristics, in vitro and in vivo behaviors, and ecotoxicological effects of engineered nanomaterials. FROM THE CLINICAL EDITOR The rapid gain in popularity of nanomaterials has also raised the concern of nanotoxicity, which needs to be assessed and addressed. In this comprehensive review, the authors outlined the underlying principles of using synchrotron radiation techniques for nanotoxicology studies and also in other scientific fields.

Nanomaterial-based approaches for the detection and speciation of mercury.

Mercury is toxic with widespread contamination. Highly sensitive and selective approaches for mercury analysis are desired. Although conventional techniques are accurate and sensitive in the determination of mercury, these procedures are time-consuming, labor-intensive and dependent heavily on expensive instrumentation. In recent years, nanomaterial-based approaches have been proved to be effective alternatives in the detection and speciation of mercury. In this review, the development of different nanomaterial-based approaches was summarized, as well as their utilization for the detection of mercury in environmental and biological samples, such as gold nanomaterials, carbon nanomaterials, quantum dots and so on. Moreover, the speciation of mercury using nanomaterials was also reviewed.

Demethylation of methylmercury in growing rice plants: An evidence of self-detoxification.

Mercury (Hg) is a global pollutant that poses a serious threat to human and the environment. Rice was found as an important source for human exposure to Hg in some areas. In this study, the transportation and transformation of IHg and MeHg in rice plants exposed to IHg or MeHg were investigated. The IHg and MeHg concentrations in rice roots and shoots collected every five days were analyzed by HPLC-ICP-MS and SR-XANES. When exposed to MeHg, the percent of IHg in rice roots and shoots increased while MeHg decreased significantly, suggesting prominent demethylation of MeHg occurred. However no notable MeHg was found in both roots and shoots of rice plant when exposed to IHg. SR-XANES analysis further confirmed the demethylation of MeHg with rice. This study provides a new finding that demethylation of MeHg could occur in growing rice, which may be a self-defense process of rice plant.

Influence of sulfur on the accumulation of mercury in rice plant (Oryza sativa L.) growing in mercury contaminated soils

Sulfur (S) is an essential element for plant growth and its biogeochemical cycling is strongly linked to the species of heavy metals in soil. In this work, the effects of S (sulfate and elemental sulfur) treatment on the accumulation, distribution and chemical forms of Hg in rice growing in Hg contaminated soil were investigated. It was found that S could promote the formation of iron plaque on the root surface and decrease total mercury (T-Hg) and methylmercury (MeHg) accumulation in rice grains, straw, and roots. Hg in the root was dominated in the form of RS-Hg-SR. Sulfate treatment increased the percentage of RS-Hg-SR to T-Hg in the rice root and changed the Hg species in soil. The dominant Hg species (70%) in soil was organic substance bound fractions. Sulfur treatment decreased Hg motility in the rhizosphere soils by promoting the conversion of RS-Hg-SR to HgS. This study is significant since it suggests that low dose sulfur treatment in Hg-containing water irrigated soil can decrease both T-Hg and MeHg accumulation in rice via inactivating Hg in the soil and promoting the formation of iron plaque in rice root, which may reduce health risk for people consuming those crops.

Identification and quantification of seleno-proteins by 2-DE-SR-XRF in selenium-enriched yeasts

A comprehensive approach that can identify and quantify selenium (Se) in seleno-proteins in Se-enriched yeast was developed. The Se-containing compounds in Se-enriched yeast were first extracted and then the fraction of Se-containing proteins in the supernatant was analyzed by 2-dimensional electrophoresis (2-DE) and synchrotron radiation X-ray fluorescence (SR-XRF). The detection limit (DL) of SR-XRF analysis for Se quantification in Se-containing proteins after 2-DE separation was calculated to be 0.20 µg g−1, which is suitable for Se quantification in the Se-containing spots present on the 2-D gel. After being scanned by SR-XRF, only spots with a mean Se content exceeding twice the DL of SR-XRF were considered to be seleno-proteins. In this way, a total of 157 Se-containing spots in the gel were visually distinguished. Se contents in all the Se-containing proteins of different molecular weights were quantified. The total Se content on the 2-D gel was calculated to be 126.56 µg g−1, which covered most of the seleno-proteins on the 2-D gel.

Accumulation and transformation of nanomaterials in ecological model organisms investigated by using synchrotron radiation techniques

Engineered nanomaterials are promising in many aspects; however, information on the potential risks of the engineered nanomaterials to the ecological system is still limited. With a wide frequency range and high brilliance, SR light sources are tunable, highly polarized, and pulsed. These made SR techniques achieve much improved signal to noise ratio, better spatial and temporal resolution and much reduced acquisition times than those using conventional light sources. In this review, the application of SR techniques to study the accumulation and transformation of engineered nanomaterials is summarized using different model organisms in ecosystems including terrestrial, aquatic and atmospheric systems.

Thiosulfate amendment reduces mercury accumulation in rice (Oryza sativa L.)

Background and aimsThiosulfate addition increases the solubility of mercury (Hg) in soil and Hg uptake by plants under oxic conditions. However, anoxic conditions could dominate the biogeochemical processes of Hg cycling during rice cultivation. The present study aimed to determine whether thiosulfate, a sulfur-containing fertilizer, could be used for Hg immobilization in paddy soil.MethodsA pot experiment was conducted using soil newly spiked with Hg and different doses of thiosulfate. Total Hg concentrations in rice tissues, Hg speciation in roots, and geochemical fraction of Hg in soils were investigated. Hydroponic cultivation was conducted to determine the subcellular distribution of Hg in root tissues.ResultsThiosulfate application significantly reduced Hg concentration in rice plants. It increased the percentage of organic-bound Hg, but decreased the percentage of iron/manganese oxide-bound Hg. Thiosulfate enhanced iron plaque formation and Hg adsorption on the iron plaque. Its application increased the percentage of Hg forms similar to HgS and decreased those similar to Hg-glutathione [Hg(GS)2].ConclusionsThiosulfate amendments had a remarkable inhibitory effect on Hg accumulation in rice plants in newly Hg-spiked soil. This occurred because thiosulfate reduced Hg mobility in the rhizosphere and root tissues, promoted the formation of iron plaque, and facilitated more Hg adsorption by the iron plaque. Our findings suggest that appropriate thiosulfate treatment could be used as Hg-immobilizing agents in paddy soil.