The risks of sulfur addition on cadmium accumulation in paddy rice under different water-management conditions

Recently, the application of sulfur (S) has been recommended to control the accumulation of cadmium (Cd) in rice in contaminated paddy soil. However, the effects of exogenous S on Cd transfer in paddy rice systems under different water-management practices have not been systematically investigated. Pot experiments were performed to monitor the composition of soil pore water and the Cd accumulation in iron plaque and rice tissue were compared under different S (0 and 200 mg/kg Na₂SO₄) and water (continuous and discontinuous flooding) treatments. Sulfur application significantly increased Cd concentrations in soil pore water under discontinuous flooding conditions, but slightly reduced them under continuous flooding. Moreover, the oxidation/reduction potential (Eh) was the most critical factor that affected the Cd levels. When the Eh exceeded −42.5 mV, S became the second critical factor, and excessive S application promoted Cd dissolution. In addition, S addition elevated the Cd levels in iron plaque and reduced the Cd transfer from the iron plaque to rice roots. In rice, S addition inhibited Cd transfer from the rice roots to the straw; thus, more Cd was stored in the rice roots. Nevertheless, additional S application increased the Cd content in the rice grains by 72% under discontinuous flooding, although this effect was mitigated by continued flooding. Under simulated practical water management conditions, S addition increased the risk of Cd contamination in rice, suggesting that S application should be reconsidered as a paddy fertilization strategy.     

Mercury transformation processes in nature: Critical knowledge gaps and perspectives for moving forward

The transformation of mercury (Hg) in the environment plays a vital role in the cycling of Hg and its risk to the ecosystem and human health. Of particular importance are Hg oxidation/reduction and methylation/demethylation processes driven or mediated by the dynamics of light, microorganisms, and organic carbon, among others. Advances in understanding those Hg transformation processes determine our capacity of projecting and mitigating Hg risk. Here, we provide a critical analysis of major knowledge gaps in our understanding of Hg transformation in nature, with perspectives on approaches moving forward. Our analysis focuses on Hg transformation processes in the environment, as well as emerging methodology in exploring these processes. Future avenues for improving the understanding of Hg transformation processes to protect ecosystem and human health are also explored.     

Biochar affects methylmercury production and bioaccumulation in paddy soils: Insights from soil-derived dissolved organic matter

Biochar has been used increasingly as a soil additive to control mercury (Hg) pollution in paddy rice fields. As the most active component of soil organic matter, soil dissolved organic matter (DOM) plays a vital role in the environmental fate of contaminants. However, there are very few studies to determine the impact of biochar on the Hg cycle in rice paddies using insights from DOM. This study used original and modified biochar to investigate their effect on DOM dynamics and their potential impact on methylmercury (MeHg) production and bioaccumulation in rice plants. Porewater DOM was collected to analyze the variations in soil-derived DOM in paddy soils. The results showed that the addition of biochar, whether in original or modified form, significantly reduced the bioaccumulation of MeHg in rice plants, especially in hulls and grains (p<0.05). However, MeHg production in soils was only inhibited by the modified biochar. Biochar addition induced a significant increase in DOM's aromaticity and molecular weight (p<0.05), which decreased Hg bioavailability. Furthermore, enhanced microbial activity was also observed in DOM (p<0.05), further increasing MeHg production in the soil. Thus, the effect of biochar on the fate of Hg cycle involves competition between the two different roles of DOM. This study identified a specific mechanism by which biochar affects Hg behavior in rice paddy soil and contributes to understanding the more general influence of biochar in agriculture and contaminant remediation.     

Understanding the excretion rates of methylmercury and inorganic mercury from human body via hair and fingernails

Effective biomarkers are necessary to better understand the human mercury (Hg) exposure levels. However, mismatched biomarker sampling method causes extra uncertainty in assessing the risk of Hg exposure. To compare the differences between hair and fingernail, and further understand the excretion rates of methylmercury (MeHg) and inorganic mercury (IHg) via hair and fingernails, the total mercury (THg), MeHg, and IHg concentrations in paired hair and fingernail samples were investigated through paired samples collected from two typical mining areas, Wanshan mercury mine area (WMMA) and Hezhang zinc smelting area (HZSA). The positive correlation in THg, MeHg, and IHg concentrations (p <0.01) between hair and fingernail samples indicated that those two biomarkers can be corrected in application of assessing human Hg exposure. Compared to fingernails, the hair was suggested to be a more sensitive biomarker as the concentration of THg, MeHg and IHg were 2 ∼ 4 times higher than those in fingernails. Furthermore, the amounts of THg, MeHg, and IHg excreted via hair were 70 ∼ 226 times higher than that excreted via fingernails, and the hair plays a more important role than fingernails in the excretion of Hg from human bodies. Present study therefore provides some new insights to better understand the fate of human assimilated Hg.     

Highly efficient Hg2+ removal via a competitive strategy using a Co-based metal organic framework ZIF-67

The stronger coordination ability of mercury ions with organic ligands than the metal ions in metal organic framework (MOFs) provides an accessible way to separate mercury ions from solution using specific MOFs. In this study, a Co-based MOF (ZIF-67, Co(mIM)₂) was synthesized. It did not introduce specific functional groups, such as -SH and -NH₂, into its structure through complicated steps. It separate Hg²⁺ from wastewater with a new strategy, which utilized the stronger coordination ability of Hg²⁺ with the nitrogen atom on the imidazole ring of the organic ligand than the Co²⁺ ions. Hg²⁺ replaced Co²⁺ nodes from ZIF-67 and formed a more stable precipitate with mIM. The experimental results showed that this new strategy was efficient. ZIF-67 exhibited Hg²⁺ adsorption capacity of 1740 mg/g, much higher than the known MOFs sorbents. mIMs is the reaction center and ZIF-67 can improve its utilization. The sample color faded from purple to white due to the loss of cobalt ion. It is a great feature of ZIF-67 that allows users to judge whether the sorbent is deactivated intuitively. ZIF-67 can be sustainable recycled by adding organic ligands to the solution after treatment due to its simple synthesis method at room temperature. It's a high-efficient and sustainable sorbent for Hg²⁺ separation from wastewater.     

A comparison of chemical mechanisms based on TRAMP-2006 field data

A comparison of a model using five widely known mechanisms (RACM, CB05, LaRC, SAPRC-99, SAPRC-07, and MCMv3.1) has been conducted based on the TexAQS II Radical and Aerosol Measurement Project (TRAMP-2006) field data in 2006. The concentrations of hydroxyl (OH) and hydroperoxy (HO₂) radicals were calculated by a zero-dimensional box model with each mechanism and then compared with the OH and HO₂ measurements. The OH and HO₂ calculated by the model with different mechanisms show similarities and differences with each other and with the measurements. First, measured OH and HO₂ are generally greater than modeled for all mechanisms, with the median modeled-to-measured ratios ranging from about 0.8 (CB05) to about 0.6 (SAPRC-99). These differences indicate that either measurement errors, the effects of unmeasured species or chemistry errors in the model or the mechanisms, with some errors being independent of the mechanism used. Second, the modeled and measured ratios of HO₂/OH agree when NO is about 1 ppbv, but the modeled ratio is too high when NO was less and too low when NO is more, as seen in previous studies. Third, mechanism–mechanism HO_x differences are sensitive to the environmental conditions – in more polluted conditions, the mechanism–mechanism differences are less. This result suggests that, in polluted conditions, the mechanistic details are less important than in cleaner conditions, probably because of the dominance of reactive nitrogen chemistry under polluted conditions.     

长江中上游护堤林发展土地潜力研究

护岸堤林建设是建设是长江中上游防护林体系建设林种空间布局与配置不可缺少的有机组成部分，具沿江而布及成连续林带的特点。其发展的土地潜力取决于岸堤线长度、林带建设宽度和建设地带内的土地利用现状结构等三个因素。研究结果表明：长江中上游研究江段护岸堤林发展土地数量潜力规模为２５１２３．４～４１９３８．９ｈｍ２，其中需造林绿化的宜林荒地地（第一类潜力）为８２１４．５～１３７５７．３ｈｍ２，需改造更新的疏灌林地和需加强抚育的未成林造林地（第二潜力）为５４０９．３～９０１５．５ｈｍ２，需退耕还林的耕地（第三类潜力）为１１４９９．６～１９１６６．１ｈｍ２。     

1975年海城地震成功预报的回顾与思考

当我们满怀激情翻开2005年的日历时，不经意地发现已进入海城地震成功预报30周年的门槛，令人们不能忘怀的是，当1975年2月4日7．3级地震强烈震撼着辽南大地时，面对灾区到处房倒屋塌的悲凉景象，震区人民并没有气馁，而是满怀豪情地抗震救灾、重建家园，描绘更为美好的建设蓝图。这种生动场面的出现是因为震前有了较为准确的地震预报。     

新形势下改革和加强中国环境保护管理体制的思考

中国现行的环境保护管理体制已无法适应日益复杂化的环境问题,改革和强化环境保护管理体制已迫在眉睫.分析了中国进行环境保护管理体制改革的必要性,提出了改革和强化体制的总体目标和基本思路,进而从管理体系、法律体系、运行机制和能力建设等方面论述了改革和强化环境保护管理体制的建议对策.     

First-trimester assessment of placenta function and the prediction of preeclampsia and intrauterine growth restriction

Preeclampsia and intrauterine growth restriction (IUGR) are major contributors to perinatal mortality and morbidity worldwide. Both are characterized by impaired trophoblastic invasion of the maternal spiral arteries and their conversion from narrow muscular vessels to wide non-muscular channels. Despite improvement in the understanding of the pathophysiology of these conditions, ability to accurately identify pregnant woman who will develop them is limited. This greatly impairs the development and testing of preventive interventions. While different measures of placental dysfunction have been associated with increased risk for adverse pregnancy outcomes, the ability of any single one to accurately predict these outcomes is poor. Developing predictive tests is further challenged by difficulty in the timing of the measurements, as both the structural and biochemical characteristics of the placenta change with increasing gestational age. The ideal screening test would accurately predict the development of adverse pregnancy outcomes early enough to provide a window for preventive interventions. Improvement in ultrasound technology provides potentially useful novel tools for evaluating placental structure, but measuresments need to be standardized in order to be useful. Maternal serum analyte screening is a noninvasive test of placental biochemical function, but present serum marker alone is not sufficiently accurate to suggest its routine use in clinical practice. The use of first trimester biochemical markers in combination with uterine artery Doppler screening is promising as a potential screening tool. Prospective longitudinal studies using standardized methodology are necessary to further evaluate the choice of parameters and strategies of combination to achieve the best predictive models. Copyright © 2010 John Wiley & Sons, Ltd.