Stable chlorine intramolecular kinetic isotope effects from the abiotic dehydrochlorination of DDT

INTENTION, GOAL, SCOPE, BACKGROUND: Identifying different sources and following reaction pathways of chlorinated organic contaminants in the environment can be challenging, especially when only their concentrations are available. Compound-specific stable chlorine measurements of some contaminants have recently been shown to provide additional information and an increased understanding of their biogeochemistry. These studies, however, have been generally limited to volatile molecules. OBJECTIVE: Here, the stable chlorine isotope ratios of the semi-volatile pesticide, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) were investigated. Specifically, the intramolecular stable chlorine isotopic compositions of DDT and the kinetic isotope effect (KIE) for the abiotic dehydrochlorination of DDT to 2,2-bis(p-chlorophenyl)-1,1-dichloroethene (DDE) were determined. METHODS: Selective chemical oxidation of DDT to dichlorobenzophenone (DCBP) and analysis of each compound was used to calculate the stable chlorine isotope ratios of the alkyl and aromatic chlorines in DDT. To determine the KIE for dehydrochlorination, DDT was reacted in a basic solution to yield DDE at 52 degrees C, 60 degrees C, and 72 degrees C for 3, 5, and 5 days, respectively. RESULTS AND DISCUSSION: Significant intramolecular stable chlorine isotopic differences were observed in one sample of DDT where the alkyl and aromatic delta 37Cl values were -5.76 +/- 0.45 and -2.21 +/- 0.24%@1000, respectively. Dehydrochlorination of DDT to DDE in basic solutions at 52, 60, and 70 degrees C resulted in a substantial intramolecular KIE where the alkyl chlorines of DDE shifted by approximately 3%@1000 relative to the alkyl chlorines in DDT. However, no temperature dependence was observed. The KIE, calculated by an iterative program, was 1.009. CONCLUSIONS: Intramolecular differences in the stable chlorine isotope ratios were observed in DDT and this is the first such finding. Dehydrochlorination of DDT yields a measurable and distinct intramolecular stable chlorine KIE. RECOMMENDATION AND OUTLOOK: The results of this study demonstrate the existence of significant intramolecular differences in chlorinated organic compounds. Many other chlorinated semi-volatile and volatile organic contaminants are synthesized from multiple sources of chlorine, and we recommend that similar studies be performed on many such molecules in order to attain a clear understanding of their intramolecular chlorine isotopic differences. The existence of a measurable KIE for the dehydrochlorination of DDT to DDE shows the potential strength of using isotopic measurements to investigate the biogeochemistry of these important compounds. For example, the isotopically depleted aqueous chloride produced by dehydrochlorination of DDT to DDE may be a useful tracer of these reactions in freshwater environments.     

聚乙烯醇固定化混合细菌细胞对印染废水脱色的研究

应用聚乙烯醇(PVA)为载体固定化混合细菌细胞以PVA浓度为12％(w/v),细胞浓度为2％(w/v)最好,pH对固定化操作过程影响不大。固定化细胞对印染废水的脱色活性与其自然细胞相似,最适温度为30—40℃,最适pH为7.0;在pH 6.0—8.0温度25—40℃范围内都具有较高的脱色活性,以及好的热稳定性;在连续一个月的印染废水脱色试验中,停留时间小于3.0h,脱色率均可维持在70—80％。     

不同静电场处理方式对大豆生物学效应的比较研究

分别研究了静电场预处理种子、静电场处理幼苗以及种子和幼苗累积静电场处理3种电场处理方式对大豆叶片叶绿素含量、过氧化物酶(POD)活性、可溶性蛋白含量、叶绿素a(Chla)荧光动力学参数和根系活力的影响.结果表明,3种静电场处理方式均能对大豆产生明显的生物学效应.其中,静电场处理种子对大豆的影响相对较小,静电场处理幼苗对大豆的影响较大,而对种子和幼苗累积静电场处理对大豆的影响最为显著.图2表1参11     

Formaldehyde in China: Production, consumption, exposure levels, and health effects

Formaldehyde, an economically important chemical, is classified as a human carcinogen that causes nasopharyngeal cancer and probably leukemia. As China is the largest producer and consumer of formaldehyde in the world, the Chinese population is potentially at increased risk for cancer and other associated health effects. In this paper we review formaldehyde production, consumption, exposure, and health effects in China. We collected and analyzed over 200 Chinese and English documents from scientific journals, selected newspapers, government publications, and websites pertaining to formaldehyde and its subsequent health effects.Over the last 20 years, China's formaldehyde industry has experienced unprecedented growth, and now produces and consumes one-third of the world's formaldehyde. More than 65% of the Chinese formaldehyde output is used to produce resins mainly found in wood products — the major source of indoor pollution in China. Although the Chinese government has issued a series of standards to regulate formaldehyde exposure, concentrations in homes, office buildings, workshops, public places, and food often exceed the national standards. In addition, there have been numerous reports of formaldehyde-induced health problems, including poisoning and cancer. The lack of quality epidemiological studies and basic data on exposed populations emphasizes the need for more extensive studies on formaldehyde and its related health effects in China.     

水库型滑坡灾害综合灾情评价模型研究

分析了滑坡事件的成灾机理,认为滑坡的灾害效应包含孕育灾害的自然环境、社会环境和自然-滑坡体-社会相互作用系统.在此基础上,将滑坡灾害综合灾情评价结构体系分为危险性评价、易损性评价、破坏损失评价、防灾减灾工程评价四个部分.针对水库型点源滑坡,建立了综合灾情评价的连续函数模型.     

四环素对微囊藻生长及光合作用的毒性效应机制

光合作用是蓝藻生长繁殖的生理基础,研究四环素胁迫下蓝藻的生长和光合作用的变化和响应,有助于揭示其作用机制。为探究四环素对微囊藻的毒性效应,对培养在0、0.1、0.2、0.5、1.0、2.0和5.0 mg·L~(-1)共7个浓度下的微囊藻的细胞数、叶绿素a含量、微囊藻光合系统Ⅱ(PSⅡ)快速光响应曲线(RLCs)及快速叶绿素荧光诱导动力学曲线(OJIP)进行了测定。结果表明,四环素处理7 d后,微囊藻的半致死浓度(LC_(50))为(0.571±0.036) mg·L~(-1)。随着四环素浓度的增加,微囊藻生长受到抑制,叶绿素含量减少,PSⅡ中单位反应中心失活。当四环素浓度高于0.5 mg·L~(-1)时,微囊藻Q_A~-到Q_B的电子传递被抑制,造成Q_A~-大量积累,影响PSⅡ的电子受体侧。然而,在低浓度四环素处理中,以吸收光能为基础的性能指数(PI_(ABS))、用于电子传递的量子产额(φ_(Eo))和最大光化学效率(φ_(Po))显著升高,用于热耗散的量子比率(φ_(Do))显著降低。这些结果表明,低浓度四环素处理时,微囊藻能通过自身调节改变PSⅡ中能量配置,改变电子传递速率,提高光合效率,从而应对低浓度四环素胁迫,而当四环素浓度较高时,微囊藻的光合作用显著降低,生长受到抑制。     

氯化铜催化二噁英生成实验及指纹特性分析

氯化铜被认为是对二■英(PCDD/F)生成促进作用最强的金属催化剂,温度和氧气含量是影响其催化二■英生成的关键因素.本文选取250～550℃间8个不同温度点及0～20%间4种不同氧气含量,系统性地研究了温度和氧气含量对含氯化铜模拟飞灰(MFA)生成二■英的影响,并通过分析指纹特性探讨二■英的生成路径和机理.结果发现,290～350℃之间二■英生成量较高,且在290℃时二■英总量达到最大值;氧气含量为10%时二■英生成量达到最高.研究二■英同分异构体分布可从分子层面为研究其生成路径和机理提供重要信息,因此,本文分析了四至八氯代PCDD/F的全部异构体的分布.结果表明,在本文所选取的温度和氧含量范围内,温度对二■英生成路径的影响高于氧气含量.最后,重点讨论了2,3,7,8位氯取代的17种有毒异构体的分布随温度和氧气的变化情况及生成路径.利用主成分分析法(PCA)证实了氯化铜催化二■英从头合成过程中存在经由氯酚路径生成的异构体,并讨论了不同工况下氯酚路径对二■英生成的影响.     

东江水库对耒水中下游原生动物的影响

为评价东江水库建成对耒水中下游水生生物的影响,１９９３年作者对东江水库坝下耒水中下游原生动物进行了两次调查。结果四个断面共发现原生动物８４种,其中丰水季（８月）５９种,多于枯水季（１０月底）的４６种,但丰水季数量（４３５个／Ｌ）和生物量（０．０３６ｍｇ／Ｌ）都低于枯水季（３．２４４个／Ｌ,０．３３５ｍｇ／Ｌ）;多样性指数与种种类数一样,多是丰水季大于枯水季。建库后,从中游到下游原生动物种类数,数量     

气候变暖背景下西南四省市暴雨洪涝灾害风险变化

为了对西南地区气候变暖前后四省市相对灾情指数变化、暴雨洪涝相对灾情概率分布和暴雨洪涝灾害致灾因子危险性风险进行评价,采用西南地区四省市83个气象站点的逐日降水和气温资料、以及灾情数据等,首先利用突变检验确定气候变化突变年,然后借助灰色关联法、信息分配法以及熵权法等进行分析.结果表明:西南地区四省市年平均气温于1998年...     

Environmental impact of biomethanogenesis

The environmental impact of biomethanogenesis is related to its ecological role, accumulation and effect as a greenhouse gas, and application in anaerobic digestion for conversion of biomass and wastes to methane and compost. Biological formation of methane is the process by which bacteria decompose organic matter using carbon dioxide as an electron acceptor in the absence of dioxygen or other electron acceptors. This microbial activity is responsible for carbon recycling in anaerobic environments, including wetlands, rice fields, intestines of animals sediments, and manures. The mixed consortium of microorganisms involved includes a unique group of bacteria, the methanogens, which may be considered to be in a separate kingdom based on genetic and phylogenetic variance from all other life forms. Because methane is a significant and increasing greenhouse gas, its source fluxes and their potential reduction are of concern. Biomethanogenesis may be harnessed for reduction of wastes and conversion of renewable resources to significant quantities of substitute natural gas which could mitigate carbon dioxide and other pollutants related to use of fossil fuels.