Dingyong Wang

The record of cosmogenic, radiogenic, fissiogenic, and trapped noble gases in recently recovered Chinese and other chondrites

Abstract We performed a comprehensive study of the noble gas isotopic abundances in thirty-six chondrites including twenty-seven chondrites recovered in China. The large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter. The comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200°C whereas ≥85% of these gases in carbonaceous chondrites are degassed at ≥ 200°C. There exists a clear correlation of the fraction of trapped Xe released at > 1200°C and petrologic type of chondrites. It thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same. The Ngawi LL3 chondrite is solar gas rich. The solar gases in meteorites and lunar surface material are mixtures of solar wind (SW) and solar energetic particles (SEP). We show that the variations of the 3 He 4 He and 20 Ne 22 Ne ratios for solar gas-rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of He and Ne or due to a change of the SW/SEP flux ratio with time. Furthermore, we demonstrate that the 81Kr concentration is a function of the shielding depth of a sample within the meteoroid. Deviations from this depth dependency curve are observed for Jilin (H5), Lishui (L5), Suizhou (L6), and Dongtai (LL6). A complex exposure history for Jilin is thus confirmed and is possible for the other three chondrites. Cosmic-ray exposure ages are calculated based on six different nuclides—3He, 21Ne, 38Ar, 83Kr, 126Xe, and 81Kr-Kr. In most cases good agreement is observed for the ages derived from the different methods. Quality classes are assigned to the exposure ages, and the age distributions are discussed. In some meteorites we observe effects induced by secondary cosmicray-produced neutrons. Epithermal neutron fluxes, Jn(30–300 eV), and fast neutron fluxes, Jn(>5 MeV), are derived based on the reactions 79Br(n, γβ)80Kr and 24Mg(n, α)21Ne, respectively; and preatmospheric masses of the meteoroids are estimated. We show that the ratio J n (30–300 eV) J n (> 5 MeV) increases with increasing preatmospheric mass. We introduce a 3He exposure age/21Ne exposure age vs. 4He gas retention age/40Ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids. Finally, in some chondrites we observe Xe produced by 244Pu fission and calculate the time span between fission-Xe retention in these chondrites and that of the Angra dos Reis achondrite. We find that the ordinary chondrites started to retain fission Xe 48 ± 30 Ma earlier than Angra dos Reis; we do not observe systematic differences between H, L, and LL or type 5 and 6 chondrites with respect to the time of fission Xe retention.

Distribution Patterns of Inorganic Mercury and Methylmercury in Tissues of Rice (Oryza sativa L.) Plants and Possible Bioaccumulation Pathways

Whole rice plants (Oryza sativa L.) were collected at different typical mercury (Hg) contaminated sites during regular harvest periods to investigate the distribution of inorganic mercury (IHg) and methylmercury (MeHg) in tissues. The whole rice plants were divided into rice seed (brown rice), hull, root, stalk and leaf. Elevated IHg and MeHg concentrations were observed in rice plants cultivated in Hg mining area compared to those obtained from the control site, which attributed to the Hg contamination of soil compartments by the historical large-scale Hg mining/smelting and ongoing artisanal Hg smelting activities. Our observations showed that Hg in ambient air was the potential source of IHg to the above ground parts, whereas IHg concentrations in root were restricted to Hg concentrations in paddy soil. The rice seed has the highest ability to accumulate MeHg compared to the other tissues. MeHg in paddy soil is a potential source to tissues of rice plant. Our study suggested that newly deposited Hg is comparatively more easily methylated than old mercury in soil.

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus).

Abstract We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day – warm temperature (16L:8D, 23 °C), (2) Long day – cold temperature (16L:8D, 5 °C), (3) short day – warm temperature (8L:16D, 23 °C), and (4) short day – cold temperature (8L:16D, 5 °C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat.

Effect of organic matter and pH on mercury release from soils

An investigation was conducted on the effect of organic matter (OM) and pH on mercury (Hg) release from soils. Hg release flux was measured using the dynamic flux chamber (DFC) combined with the Lumex multifunctional mercury analyzer in both laboratory experiment and field monitoring. The results showed that Hg emission from the OM-added soils was apparently low because of the high affinity of OM to Hg, resulting in the reverse order as the amount of OM addition. Meanwhile, Hg release flux from different pH value soils exhibited the same trend for both Hg(2+) and Hg2(2+) treatment, increasing the Hg flux with pH value of soils increasing. The trend of Hg release in the pH dependence experiment has been well in agreement with that from the field test. In addition, Hg release seemed to be related to its species in the soil, the flux from Hg(2+)-added soil was obviously higher than that of Hg22z-added soil by the laboratory experiment.

Inorganic mercury accumulation in rice (Oryza sativa L.)

To investigate the source and process of inorganic mercury (IHg) accumulation in rice, we monitored the concentrations of IHg in tissues of rice plants (Oryza sativa L.) from four experimental plantation plots. Biweekly during the rice-growing season, tissues of rice plants, corresponding soil, precipitation, and irrigation water samples were collected. The sampling data support the following: (1) the atmosphere is the principal source of IHg to the aboveground parts of the rice plant; (2) both the atmosphere and soil contribute to IHg content in stalks, but the former source tends to be more important; and (3) soil is the major source of root IHg content. These observations and the fact that the gradually increasing concentration and mass of IHg in stalks and leaves during the rice-growing season suggested that atmospheric Hg could be absorbed by and incorporated into the aboveground parts of the rice plant and that limited or no Hg emission to the air or translocation to the soil occurred after deposition of atmospheric Hg. The root surface acted as a potential Hg barrier and consequently reduced the translocation of Hg ion mass through the root system to the aboveground parts. Accumulated IHg in aboveground parts of rice plants cannot be transported to seeds, which is completely different from the case of methylmercury.

Mercury emission to atmosphere from primary Zn production in China.

Emissions of mercury (Hg) to air have regional and global impacts through long range transport in the atmosphere. Primary Zn production is regarded as an important anthropogenic Hg source in China, but research on its Hg emission is limited. To gain a better understanding of Hg emissions from Zn production activities in China, field investigations at four industrial-scale Zn production plants using electrostatic process with Hg removal (HP-WR), electrostatic process without Hg removal (HP-WOR), retort Zn production (RZ), imperial smelting process (ISP), and one artisanal Zn smelting process (AZ) were carried out. In the investigation, Hg emission factors are defined as how much Hg was emitted to the atmosphere per ton Zn produced during various Zn production methods and were estimated by using mass balance method. The results showed that the estimated Hg emission factors of Zn production were 5.7+/-4.0 g Hg t(-1) Zn for HP-WR, 31+/-22 g Hg t(-1) Zn for HP-WOR, 34+/-71 g Hg t(-1) Zn for RZ, 122+/-122 g Hg t(-1) Zn g t(-1) for ISP, and 75+/-115 g Hg t(-1) Zn for AZ. Approximately 80.7-104.2 t year(-1) of Hg was emitted to atmosphere from primary Zn production during the period of 2002-2006 in China.

Effect of dissolved organic matter on adsorption and desorption of mercury by soils.

Effects of dissolved organic matter (DOM) on adsorption and desorption of Hg were investigated in two kinds of soils, Xanthi-Udic Ferralosols (XUF) and Typic Purpli-Udic Cambosols (TPUC). The DOM was obtained from humus soil (DOMH), rice straw (DOMR), and pig manure (DOMP). The presence of DOM obviously reduced Hg maximum adsorption capacity with up to 40% decreases over the control, being an order of DOMH (250.00 mg/kg) < DOMR (303.03 mg/kg) < DOMP (322.58 mg/kg) < CK (control 416.67 mg/kg) for the XUF and DOMH (270.27 mg/kg) < DOMR (312.50 mg/kg) < DOMP (324.23 mg/kg) < CK (476.11 mg/kg) for the TPUC, respectively. The inhibition of DOM on Hg adsorption was slightly weaker in XUF than in TPUC. Meanwhile, the DOM promoted Hg desorption from the soils. The kinetic models, the Two-constant equation and Elovich equation, were applicable to describe the adsorption and desorption processes of Hg in soils. The speed of Hg adsorption was consistently slowed down by the existence of DOM.

Mercury in some chemical fertilizers and the effect of calcium superphosphate on mercury uptake by corn seedlings (Zea mays L.).

Mercury (Hg) contents in ten chemical fertilizers were determined, and the effect of calcium superphosphate (CSP) on the uptake and translocation of Hg in corn seedlings was investigated by pot experiments. CSP was applied at the levels of 0, 66.7, and 133.4 mg P2O5/kg to Hg-treated (2 mg/kg) and untreated soils. CSP had the highest Hg content (5.1 mg/kg), followed by the NPK compound fertilizer 15-5-5 (15% N, 5% P2O5, 5% K2O) (1.2 mg/kg), then by nitrogen fertilizers (except for ammonia sulfate) and potassium fertilizers. Application of CSP did not obviously influence the biomass of corn roots, but it significantly increased the biomass of corn shoots in Hg-treated soil. Application of CSP at the levels of 66.7 and 133.4 mg P2O5/kg did not obviously influence the uptake of Hg by corn seedlings on soils without Hg treatment, but it decreased the Hg uptake of corn seedlings significantly on Hg-treated soils. The transfer coefficient of Hg in corn seedlings improved slightly on soils without Hg treatment, but decreased slightly on Hg-treated soils with the application of CSP. These results implied that CSP could ameliorate Hg toxicity to corn seedlings by inhibiting the uptake and the translocation of Hg in plants on Hg-polluted soils.

Mercury methylation in rice paddies and its possible controlling factors in the Hg mining area, Guizhou province, Southwest China ☆

Understanding mercury (Hg) methylation/demethylation processes and the factors controlling methylmercury (MeHg) production within the rice paddy ecosystem of Hg mining areas is critical to assess the risk of MeHg contamination in rice grain. Two typical Hg-contaminated mining sites, a current-day artisanal site (Gouxi) and an abandoned site (Wukeng), were chosen in this study. We qualified the in situ specific methylation/demethylation rate constants in rice paddy soil during a complete rice-growing season. Our results demonstrate that MeHg levels in rice paddy soil were a function of both methylation and demethylation processes and the net methylation potential in the rice paddy soil reflected the measured MeHg production at any time point. Sulfate stimulating the activity of sulfate-reducing bacteria was a potentially important metabolic pathway for Hg methylation in rice paddies. We suggest that bioavailable Hg derived from new atmospheric deposition appears to be the primary factor regulating net MeHg production in rice paddies.

Photo-degradation of monomethylmercury in the presence of chloride ion

Photo-degradation (PD) of monomethylmercury (MMHg) is recognized as the most important process in mercury cycling that maintains MMHg at low concentration in water systems. Chloride ion (Cl(-)) is present widely in ecosystems and it may have an effect on MMHg PD. In this investigation, MMHg PD with various Cl(-) concentrations under different light radiation intensity and wavelength were performed in a quartz cylinder reactor. Various light radiations were obtained from xenon and ultraviolet (UV) bulbs. The results showed that the first order reaction coefficient decreased (1.35-0.37 h(-1)) with Cl(-) concentrations, and increased (0.14-0.76 h(-1)) with UV-B radiation intensity. The wavelength mediated PD rates varied from 0.29 h(-1) to 0.96 h(-1). The peak emission of Hg(0) was excited by UV-B radiation and Hg(0) flux of the reactions without Cl(-) (94.06 ng) was higher than that with Cl(-) by 1-4 times. All the results suggest that Cl(-) could block MMHg PD and subsequently influence the end products from PD. The wavelength and light intensity have a significant effect on MMHg PD and Hg(0) emission. Calculation of MMHg species (%) at initial and terminal time with various Cl(-) concentrations show that MMHg species changed by Cl(-) complexation and thus result in different PD mechanisms and pathways.