Terrestrial mercury transformation in the Tibetan Plateau: New evidence from stable isotopes in upland buzzards.

Understanding the geochemical cycle of mercury (Hg) in the high-altitude Tibetan Plateau is of great value for studying the long-range transport of Hg. Herein, speciation and isotopic compositions of Hg in the muscle and feathers of upland buzzards (Buteo hemilasius) were studied to trace the terrestrial transformation of Hg in the Tibetan Plateau. Very low Hg content and relatively low δ202Hg values (feather: -0.77 ± 0.50‰, n = 9, muscle: -1.29 ± 0.29‰, n = 13, 1SD) were observed in upland buzzards. In contrast, the Δ199Hg values could be as high as 2.89‰ in collected samples. To our knowledge, this is the highest Δ199Hg value reported in avian tissues. Moreover, upland buzzards showed significantly different Δ199Hg values from fish collected from the same region, suggesting different generation and transformation processes of methylmercury (MeHg) in terrestrial and aquatic ecosystems. We speculated that different percentages of Hg undergoing photochemical reactions and contributions of atmospheric MeHg were possible reasons for observed differences. The results provide new clues for different circulation histories of Hg in terrestrial and aquatic ecosystems, which will be critical for further study of geochemical cycle and ecological risk of Hg in the environment.

The Effect of Structural Diversity on Ligand Specificity and Resulting Signaling Differences of Estrogen Receptor α.

Numerous chemicals have been reported to exert estrogen-like endocrine disrupting effects via a receptor binding mechanism that directly interacts with the ligand binding domain of estrogen receptor α (ERα). However, not only their binding affinities to ERα but also their interference in specific cell and tissue functions are clearly different. In this regard, significant regulation differences among three representative estrogenic chemicals (diethylstilbestrol (DES), bisphenol A (BPA), and diarylpropionitrile (DPN)), well-known ERα agonists with very similar structures, have been observed. Molecular dynamics simulation is used to explore the underlying mechanism of different regulation effects induced by the similar estrogen-like chemicals. The DES-induced 12 Å motion of the H9-H10 loop markedly expands the negative electrostatic potential surface of the AF-2 domain, which is consistent with the over-regulation effect of the agonist. In comparison, the 3 Å motion induced by BPA and DPN corresponds to the low-regulation effect of the chemicals. Cross-correlation analysis indicates that the different ERα motions and resulting surface feature of AF-2 domain are brought by the distinguished binding modes of the agonists. Moreover, only hydrophobic DES with estrogen-like size and flexibility has a high binding affinity of -23.47 kcal/mol binding free energy. Both the hydrophilic group in DPN and the small molecular size of BPA dramatically decrease the agonist binding ability, and their binding free energies are only -12.43 kcal/mol and -11.82 kcal/mol, respectively. Our study demonstrates that similar chemicals interact differently with ERα and induce different allosteric effects, which explains the observed regulation diversity.

Mercury isotopic compositions of mosses, conifer needles, and surface soils: Implications for mercury distribution and sources in Shergyla Mountain, Tibetan Plateau.

Understanding the distribution and sources of mercury (Hg) in the Tibetan Plateau is of great value to study the long-range transport of Hg. Herein, the total Hg (THg) concentrations and the isotopic compositions of mosses, conifer needles, and surface soils collected from both slopes of the Shergyla Mountain of Tibetan Plateau were analyzed. The contents of THg in samples (except mosses on the eastern slope) were significantly positively correlated with altitude in both the western and eastern slopes, possibly caused by topographic factors. In contrast, Δ199Hg in samples was significantly negatively correlated with altitude. On the basis of Hg isotopic compositions, atmospheric Hg0 uptake was indicated as the primary accumulation pathway of Hg in mosses (Δ199Hg: -0.12 ±â€¯0.09‰, -0.26 - 0.00‰, 1 SD, n = 10) and conifer needles (Δ199Hg: -0.21 ±â€¯0.08‰, -0.36 - -0.11‰, 1 SD, n = 9). Moreover, the contributing fractions of atmospheric Hg0 to Hg in surface soils (Δ199Hg: -0.20 ±â€¯0.07‰, -0.31 - -0.06‰, 1 SD, n = 17) increased with altitude and accounted for an average of 87 ± 9% in atmospheric sources. Due to the special geographic positions and environmental conditions of the Tibetan Plateau, the results of this study were essential for further understanding the long-range transport and global cycling of Hg.

Characterization and speciation of mercury in mosses and lichens from the high-altitude Tibetan Plateau.

The accumulation and species of mercury (Hg) in mosses and lichens collected from high-altitude Tibetan Plateau were studied. The altitudes of the sampling sites spanned from 1983 to 5147 m, and a total of 130 mosses and 52 lichens were analyzed. The total mercury (THg) contents in mosses and lichens were in the ranges of 13.1-273.0 and 20.2-345.9 ng/g, respectively. The average ratios of methylmercury (MeHg) in THg in mosses and lichens were 2.4 % (0.3-11.1 %) and 2.7 % (0.4-9.6 %), respectively, which were higher than those values reported in other regions. The contents of THg in both mosses and lichens were not correlated with the THg in soils (p > 0.05). The lipid contents displayed a significantly positive correlation with concentrations of MeHg in mosses (r = 0.461, p < 0.01, n = 90), but not in lichens. The correlations between Hg contents in mosses and the altitudes, latitudes and longitudes of sampling sites indicated the mountain trapping and spatial deposition of Hg in the Tibetan Plateau.

Studies on the toxicological effects of PFOA and PFOS on rats using histological observation and chemical analysis.

As an emerging class of environmentally persistent and bioaccumulative contaminants, perfluorinated compounds (PFCs), especially perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), have been ubiquitously found in the environment. Increasing evidence shows that the accumulated levels of PFCs in animals and the human body might cause potential impairment to their health. In the present study, toxicological effects of PFOA and PFOS on male Sprague-Dawley rats were examined after 28 days of subchronic exposure. Abnormal behavior and sharp weight loss were observed in the high-dose PFOS group. Marked hepatomegaly, renal hypertrophy, and orchioncus in treated groups were in accordance with the viscera-somatic indexes of the liver, kidney, and gonad. Histopathological observation showed that relatively serious damage occurred in the liver and lung, mainly including hepatocytic hypertrophy and cytoplasmic vacuolation in the livers and congestion and thickened epithelial walls in the lungs. PFOA concentrations in main target organs were in the order of kidney > liver > lung > (heart, whole blood) > testicle > (spleen, brain), whereas the bioaccumulation order for PFOS was liver > heart > kidney > (whole blood) > lung > (testicle, spleen, brain). The highest concentration of PFOA detected in the kidney exposed to 5 mg/kg/day was 228+/-37 microg/g and PFOS in the liver exposed to 20 mg/kg/day reached the highest level of 648+/-17 microg/g, indicating that the liver, lung, and kidney might serve as the main target organs for PFCs. Furthermore, a dose-dependent accumulation of PFOS in various tissues was found. The accumulation levels of PFOS were universally higher than PFOA, which might explain the relative high toxicity of PFOS. The definite toxicity and high accumulation of the tested PFCs might pose a great threat to biota and human beings due to their widespread application in various fields.

Interaction of methylmercury and selenium on the bioaccumulation and histopathology in medaka (Oryzias latipes).

Interaction of methylmercury and selenium in medaka (Oryzias latipes) on bioaccumulation of pollutants and histopathological changes in liver and gill were studied. Juvenile medaka fish were submitted to a series of waterborne methylmercury chloride (MMC), sodium selenite (Na(2)SeO(3)) and their mixture for 210 days, respectively. The methylmercury (MeHg) and selenium contents in the whole body of medaka were determined. The dose- and time-dependent increase of MeHg and selenium contents in medaka were observed. Histopathological changes, such as edema, vacuoles, pyknotic nucleus, and telangiectasis, could clearly be observed in the slices from the exposed medaka's liver and gill. Concurrent exposure to MMC and Na(2)SeO(3) showed the increased selenium accumulation. When the exposure molar ratio of MeHg:Se was about 1, the interaction between MeHg and selenium offered a limited protection against the serious intoxication of both MMC and Na(2)SeO(3) to medaka.

Methylmercury accumulation, histopathology effects, and cholinesterase activity alterations in medaka (Oryzias latipes) following sublethal exposure to methylmercury chloride.

A series of specific toxicological effects including bioaccumulation of the pollutant, histological changes and influences on cholinesterase (ChE) activities were examined in the adult Japanese medaka after the exposure to graded sublethal concentrations (40, 20, 10, 5, 2.5ngHg/mL) of methylmercury chloride (MMC). Methylmercury (MeHg) contents in the exposed medaka tissues ranged from 0.03 to 64.4µgHg/g (wet weight, w.w.). High concentrations of MeHg were accumulated in the liver and brain, while the concentrations in muscle and fat were relatively low. A dose-dependent and exposure time-dependent increase of MeHg contents in tissues was observed. Histopathological changes, such as oedema, vacuolization, pyknotic nucleus, telangiectasis, and degenerative sperm, can clearly be observed in the slices from the liver, gill, and male gonad of the exposed medaka. Inhibition of ChE activity was common in the exposed fish's brain, liver, gill, and muscle. The serious intoxication of MMC to medaka was definitely demonstrated herein.