高原湖泊沉积物碳酸盐稳定同位素及孔隙水碳酸盐体系地球化学研究

在沉积物早期成岩作用过程中，扩散、对流和化学反应等动力学因素共同影响着孔隙水的化学平衡性质，使孔隙水在水－沉积物界面附近出现方解石不饱和现象，而在深部却呈饱和状态。从云贵高原的洱海、泸沽湖和红枫湖等湖泊的研究可以发现：在方解石不饱和带中，孔隙水的HCO_3~-和Ca~(2+)的浓度梯度比值大于理论值（1.34），HCO_3~-和Ca~(2+)的垂直分布可以用非线性常微分方程组（3-10）来描述。对寄宿时间较长的非封闭湖泊，沉积物碳酸盐的C、O稳定同位素变化特征可以用δ~（13）C-δ~（13）O模式图表示出来；特别当输入寄宿时间与蒸发寄宿时间的比值较大时，随沉积深度的不同，碳酸盐的δ~（13）C和δ~（13）O值可能呈正相关波动变化，其δ~（13）O能够反映了湖区气温变化的特征。

贵阳近效水稻田甲烷的释放通量及其碳同位素组成的研究

全球环境问题越来越引起人们的关注，其中的温室效应气体是最引人注目的环境问题之一。近年来，大气中温效应气体的增多导致全球气候的变化。甲烷作为一种重要的温室效应气体，在大气中的浓度也连续增加。据观测，大气中甲烷浓度的年增长率为1%。甲烷不仅是一种重要的温室效应气体，而且还是一种重要的化学活性成分，它在大气中的化学过程影响了大气化学的成分。由于甲烷的重要作用，研究大气甲烷的来源及增加的原因成了学术界十分热门的领域，尤其是识别大气甲烷的来源和人力活动的释放显得更为有意义。水稻田释放的甲烷是大气甲烷的重要来源之一。目前，对水稻田释放的甲烷虽进行了许多研究，然而都是个别的、不连续的观测，根据这些数据估计全球水稻田释放甲烷总量的可靠性差，尤其是象我国这样一个水稻种植大国（水稻种植面积占全球水稻面积的22%），才刚刚开始对这一领域进行研究。因此，为了对我国水稻田释放的甲烷有一个较全面的认识以及为“八五”国家重大基础课题“中国环境未来演变趋势的研究”第三题奠定一些基础，本文于1991年水稻生长期间（6-9月）对贵阳近效水稻田释放的甲烷进行了研究，并且希望通过开展对甲烷稳定同位素的研究来识别甲烷的来源。利用透明有机玻璃为材料，自行设计了一套采样系统，收集的气体样品装于气袋内。而对甲烷碳同位素的测定，则尝试用化学方法在田间进行样品的处理，将稻田释放的甲烷直接转换成碳酸锶固体样品，以便于保存和运输。在整个实验过程中，共收集了160个样品，对甲烷释放率的日变化及季节变化进行了研究。甲烷释放率最高时达71.9mg/m~2.h，而最低只有3.0mg/m~2.h。平均释放率为15.6mg/m~2.h。在此期间，对10cm以下土壤温度、水温、大气温度和水稻生长情况作了记录，对土壤有机质含量和土壤质地进行了分析，试图揭示出水稻田甲烷释放的规律及影响水稻田甲烷释放的因素，并对所得出的结论作出进一步的讨论。经过研究发现，水稻田甲烷释放率在一日之内的变化有一定的规律。几次24小时的连续观测，都显示出一日之内甲烷释放率的最大值出现在凌晨或夜晚，而在正午阳光最强烈时甲烷释放率偏低。这一结果同文献报导的有一定偏差，可用甲烷的产生、输送和转化机制对这一现象定性地加以解释。稻田甲烷的排放率除了有日变化之外，还有明显的季节。在整个水稻生长期间，甲烷的释放率除了几天尺度的小波动外，还有三个明显的高甲烷排放期。第一个排放峰值出现在插秧后的分蘖期，即六月中旬，第二、第三个峰值分别出现在七月下旬和八月中旬。其中，第一个峰值最大，第三个峰值最小。当水稻种植需排水晒田时，甲烷释放率明显下降，复水后，甲烷释放率又增加。对稻田总有机碳和活性有机碳的分析揭示出，活性有机碳同甲烷的释放率之间有一定的相关关系。在活性有机碳含量高时，甲烷的释放率也越大，但总有机碳含量与甲烷释放率之间关系不明显。在水稻生长期间，甲烷释放率也显示出较大的日变化幅度。在排放峰值期间，日变化幅度最大，最高时达59.0mg/m~2.h，出现在第一排放峰值期间。收获前，日变化幅度最小，只有0.3mg/m~2.h。温度对甲烷释放率有一定的影响，在水稻生长期里，大气温度及土壤温度的变化趋势同甲烷释放率的季节变化比较一致。根据本文的测量结果，对贵州省水稻田的甲烷释放量进行了一个很粗略的估计，约为6.96 * 10~10克/年。在甲烷碳同位素组成的测定，本文采用化学方法对样品进行前处理，这种方法用于开展稳定同位素的工作是一种新的尝试。但由于缺乏经验，时间紧，只得到几个可供测试的样品，质谱的测定结果重现性不好，使得这一尝试的结果不令人满意。在测定甲烷碳同位素的同时，对土壤中有机质和空气的中CO_2的碳同位素也进行了测量，结果表明，土壤有机碳同位素较接近，为-20%左右，而空气CO_2由于光合作用与呼吸作用之故，白天和夜晚存在着差异，白天的δ~（13）C为-25%左右，夜晚δ~（13）C为-29%左右。通过建立一套系统和方法，对水稻田释放的甲烷进行了研究，对这一领域有一初步的认识，为今后系统地开展这一领域的研究奠定了基础。由于是初次开展地表生物源释放气体的研究，难免存在一些问题和不足，将在以后的更深入的研究中加以改进和提高。

痕量甲烷碳同位素真空制样系统的研制与贵州省一些水稻田甲烷碳同位素组成的初步测定

甲烷碳同位素（δ~(13)C）在辩识甲源汇和提示甲烷的产出机理、传输途径方面有重要作用国内因痕量甲烷的同位素制样问题未能开展有关的研究工作。我们研制了一套痕量甲烷碳同位素的真空制样系统，并对贵州省内一些水稻田的甲烷δ~(13)C值作了初步测定。痕量甲烷碳同位素真空制样系统充分考虑到气样中CO_2、H_2O、CO和非甲烷烃等杂质气体对甲烷同位素制样的干扰，在吸收和借鉴前人工作基础上研制出来，在设计上具有以下特点：（1）制样过程中杂质气体的清除采用多环“冷阱串”，保证冷冻过程的可靠性和稳定性。（2）甲烷的高温转化使用了新型HA-02贵金属催化剂，实验检测表明：在较低的温度下（400 ℃ - 500 ℃）HA-02催化剂能确保甲烷的充分氧化分解。（3）CO_2气样设计有样品管和熔封管两种接收方式，便于收集和贮存。（4）真空制样系统可以制备气样中CO_2、CO的同位素样本，与质谱仪配合可以同步监测CO_2、CO的碳氧同位素组成。同位素条件检测实验证明了痕量甲烷碳同位素真空制样的可行性。用自行研制的真空系统对贵州省内一些水稻田甲烷的δ~(13)C值初步测定表明：稻田甲烷以富集轻同位素为特征，δ~(13)C变化在-54.05 ～ -64.47‰，平均为-60.67 ± 3.56‰，比较接近肯尼亚水稻田的研究结果，同时甲烷δ~(13)C值在一天中从上竿到晚上有逐步富集~(13)C的趋势。

非生物成因天然气的稳定同位素地球化学特征与判据

本采自松辽盆地的天然气进行了化学组分和氦、碳同位素分析。经空气校正后的氦同位素组成为 ~3He/~4He＝0.26 * 10~(-6)～7.48 * 10~(-6)，相应的幔源氦的贡献额为 2.3%～63%，显示了明显的幔源氦信息，表明松辽盆地天然气藏中有幔源挥发份加入。烃类气藏甲烷的灿位素组成为 δ~(13)C＝-53.3‰～-16.7‰，δ~(13)C小于-25‰ 的甲烷是生物成因的产物，δ~(13)大于-25‰的甲烷则可能是非生物成因的。甲烷及其同系物的碳同位素组成存在两类不同的分配模式。正序排列的分析模式，即 δ~(13)C_(CH_4) < δ~(13)C_(C_2H_6) < δ~(13)C_(C_3H_8) < δ~(13)C_(C_4H_(10))，表明了生物成因天然气的特征，而反序排列的分配模式，即 δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10))的存在则暗示了松辽盆地存在非生物成因的商业天然气藏。模拟原始太阳星云中地球吸积区条件进行了原始宇宙成因烃类的合成实验（费托反应）。对合成气进行了碳同位素组成分析，并结合反应机理讨论了费托反应中碳同位素的分馏和原始宇宙成因烃类的碳同位素分配模式。反应合成气中二氧化碳具有最重的碳同位素组成。甲烷及其同系物的碳同位素分配模式具有与生物成因烃类完全不同的反序排列特征，即 δ~(13)C_(CH_4) > δ~(13)C_(C_2H_6) > δ~(13)C_(C_3H_8) > δ~(13)C_(C_4H_(10))，这表明由原始宇宙成因烃类构成的非生物成因天然气中甲烷及其同系物的碳同位素分配的反序排列的。对非生物成因天然气的判识应依靠多项指标。作为灵敏的幔源挥发份示踪剂的氦同位素是非生物成因天然气有效的间接指示剂，甲烷及其同系物碳同位素的反序排列分配模式加上重的碳同位素组成可作为非生物成因天然气的可靠的内在指标。松辽盆地的区域构造特征，天然气中显著的幔源氦的存在，较重的甲烷同位素组成 (δ~(13)C_(CH_4) > -25‰)和甲烷及其同系物碳同位素的反序排列充分证明了松辽盆地存在非生物成因的商业天然气藏。

A feasibility study evaluating docetaxel-based sequential and combination regimens in the adjuvant therapy of node-positive breast cancer

BACKGROUND AND PURPOSE: Docetaxel is an active agent in the treatment of metastatic breast cancer. We evaluated the feasibility of docetaxel-based sequential and combination regimens as adjuvant therapies for patients with node-positive breast cancer. PATIENTS AND METHODS: Three consecutive groups of patients with node-positive breast cancer or locally-advanced disease, aged < or = 70 years, received one of the following regimens: a) sequential A-->T-->CMF: doxorubicin 75 mg/m2 q 3 weeks x 3, followed by docetaxel 100 mg/m2 q 3 weeks x 3, followed by i.v. CMF days 1 + 8 q 4 weeks x 3; b) sequential accelerated A-->T-->CMF: A and T were administered at the same doses q 2 weeks; c) combination therapy: doxorubicin 50 mg/m2 + docetaxel 75 mg/m2 q 3 weeks x 4, followed by CMF x 4. When indicated, radiotherapy was administered during or after CMF, and tamoxifen started after the end of CMF. RESULTS: Seventy-nine patients have been treated. Median age was 48 years. A 30% rate of early treatment discontinuation was observed in patients receiving the sequential accelerated therapy (23% during A-->T), due principally to severe skin toxicity. Median relative dose-intensity was 100% in the three treatment arms. The incidence of G3-G4 major toxicities by treated patients, was as follows: skin toxicity a: 5%; b: 27%; c: 0%; stomatitis a: 20%; b: 20%; c: 3%. The incidence of neutropenic fever was a: 30%; b: 13%; c: 48%. After a median follow-up of 18 months, no late toxicity has been reported. CONCLUSIONS: The accelerated sequential A-->T-->CMF treatment is not feasible due to an excess of skin toxicity. The sequential non accelerated and the combination regimens are feasible and under evaluation in a phase III trial of adjuvant therapy.

Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing.

Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction. In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH(4) L(-1) (n = 26), a potential explosion hazard; in contrast, dissolved methane samples in neighboring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mg L(-1) (P < 0.05; n = 34). Average δ(13)C-CH(4) values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (-37 ± 7‰ and -54 ± 11‰, respectively; P < 0.0001). These δ(13)C-CH(4) data, coupled with the ratios of methane-to-higher-chain hydrocarbons, and δ(2)H-CH(4) values, are consistent with deeper thermogenic methane sources such as the Marcellus and Utica shales at the active sites and matched gas geochemistry from gas wells nearby. In contrast, lower-concentration samples from shallow groundwater at nonactive sites had isotopic signatures reflecting a more biogenic or mixed biogenic/thermogenic methane source. We found no evidence for contamination of drinking-water samples with deep saline brines or fracturing fluids. We conclude that greater stewardship, data, and-possibly-regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.

Fertilización nitrógeno - azufrada y variabilidad genotípica en el rendimiento y la calidad de grando en Colza - Granola (Brassica napus L.)

La difusión del cultivo de colza-canola en Argentina es aún limitada, siendo los bajos rendimientos en grano a nivel de producción una de las principales causas de la escasa adopción. Esto es consecuencia del desconocimiento de las respuestas a factores del ambiente que determinan el rendimiento y sus componentes, y a la oferta de nutrientes como estrategias para maximizar el rendimiento y la calidad comercial de los granos. Los objetivos del presente trabajo fueron analizar (i) la variabilidad en rendimiento y calidad del grano en un amplio rango de genotipos comerciales de colza-canola de Argentina, (ii) el efecto de la fertilización con nitrógeno y azufre sobre el rendimiento y (iii) la calidad del grano de dos genotipos primaverales; en un total de tres años en el campo experimental del Dto. de Producción Vegetal de FAUBA. Se halló una importante variabilidad en el rendimiento en grano entre genotipos y años, mientras que la calidad resultó más estable ante cambios del ambiente. Tanto el rendimiento como el porcentaje de aceite y ácido linolénico del grano se redujeron con temperaturas medias mayor a 13 º C durante la etapa de postfloración, resultando éste el factor ambiental preponderante, covariando con la radiación incidente. La fertilización nitrogenada (hasta 280 kg N ha-1 aplicados durante todo el ciclo) aumentó el rendimiento en grano, a través de cambios en la biomasa aérea total y el número de granos por unidad de área, sin afectarse la partición a raíz y a grano, la eficiencia de uso de la radiación ni el peso del grano. Las distintas eficiencias de uso del N (agronómica, de absorción y fisiológica) fueron constantes en ambos genotipos, y no se alteraron por la oferta de S. Los niveles de S explorados (de 9 a 69 kg ha-1) no parecieron ser limitantes para generar diferenciales en el rendimiento y la calidad del grano. El porcentaje de aceite se redujo y el de proteínas se incrementó más que proporcionalmente ante aumentos en la disponibilidad de N, mientras que el perfil de ácidos grasos y el contenido de glucosinolatos se mantuvieron estables. Los resultados de esta tesis permiten concluir que bajo las condiciones ambientales evaluadas es posible obtener altos rendimientos y alta calidad de grano de colza-canola con los genotipos disponibles actualmente en el mercado argentino

Consecuencias del reemplazo de ecosistemas naturales sudamericanos por forestaciones y pasturas megatérmicas : efectos sobre el carbono orgánico edáfico

Los cambios de uso de la tierra afectan los contenidos de carbono orgánico del suelo (COS), alterando tanto las entradas como las salidas de C en el suelo. En esta tesis se analizó, a partir de una revisión bibliográfica, el efecto a nivel regional de diferentes factores (precipitación, temperatura y edad de implantación) sobre los cambios en los contenidos de COS ocurridos al reemplazar la vegetación nativa por forestaciones o pasturas subtropicales. En un experimento a campo se evaluó el efecto del reemplazo recíproco de vegetación herbácea y leñosa sobre los cambios en los contenidos de COS. A su vez, también se evaluó el efecto de los ingresos y egresos de C (utilizando modelos con isótopos de (13 C), así como la productividad de la vegetación (estimada a partir de sensores remotos), sobre los cambios ocurridos en los contenidos de COS. Los resultados obtenidos mostraron que los cambios en los contenidos de COS superficiales son independientes del tipo de vegetación nativa que es reemplazada. A su vez, las forestaciones ganaron C en zonas áridas pero perdieron C en zonas húmedas, siendo mayores las pérdidas a mayores precipitaciones. Las pasturas aumentaron los contenidos de COS en superficie, incrementando las ganancias con las precipitaciones, sin embargo en profundidad perdieron COS cuando reemplazaron ecosistemas de selva. Tanto en pasturas como forestaciones las ganancias de COS aumentaron con la edad de implantación, sugiriendo que el equilibrio entre entradas y salidas de C al suelo es alcanzado a edades avanzadas de las plantaciones. En todas las transiciones estudiadas los ingresos de C (y no los egresos), junto con la productividad subterránea, explicaron los cambios en los contenidos de COS ocurridos luego del cambio de uso, mientras que inesperadamente la tasa de mineralización del COS fue similar en todas ellas.

Fertilización nitrógeno - azufrada y variabilidad genotípica en el rendimiento y la calidad de grando en Colza - Granola (Brassica napus L.)

La difusión del cultivo de colza-canola en Argentina es aún limitada, siendo los bajos rendimientos en grano a nivel de producción una de las principales causas de la escasa adopción. Esto es consecuencia del desconocimiento de las respuestas a factores del ambiente que determinan el rendimiento y sus componentes, y a la oferta de nutrientes como estrategias para maximizar el rendimiento y la calidad comercial de los granos. Los objetivos del presente trabajo fueron analizar (i)la variabilidad en rendimiento y calidad del grano en un amplio rango de genotipos comerciales de colza-canola de Argentina, (ii)el efecto de la fertilización con nitrógeno y azufre sobre el rendimiento y (iii)la calidad del grano de dos genotipos primaverales; en un total de tres años en el campo experimental del Dto. de Producción Vegetal de FAUBA. Se halló una importante variabilidad en el rendimiento en grano entre genotipos y años, mientras que la calidad resultó más estable ante cambios del ambiente. Tanto el rendimiento como el porcentaje de aceite y ácido linolénico del grano se redujeron con temperaturas medias mayor a 13 º C durante la etapa de postfloración, resultando éste el factor ambiental preponderante, covariando con la radiación incidente. La fertilización nitrogenada (hasta 280 kg N ha-1 aplicados durante todo el ciclo)aumentó el rendimiento en grano, a través de cambios en la biomasa aérea total y el número de granos por unidad de área, sin afectarse la partición a raíz y a grano, la eficiencia de uso de la radiación ni el peso del grano. Las distintas eficiencias de uso del N (agronómica, de absorción y fisiológica)fueron constantes en ambos genotipos, y no se alteraron por la oferta de S. Los niveles de S explorados (de 9 a 69 kg ha-1)no parecieron ser limitantes para generar diferenciales en el rendimiento y la calidad del grano. El porcentaje de aceite se redujo y el de proteínas se incrementó más que proporcionalmente ante aumentos en la disponibilidad de N, mientras que el perfil de ácidos grasos y el contenido de glucosinolatos se mantuvieron estables. Los resultados de esta tesis permiten concluir que bajo las condiciones ambientales evaluadas es posible obtener altos rendimientos y alta calidad de grano de colza-canola con los genotipos disponibles actualmente en el mercado argentino

Botany origin and protein content of homemade honeys from Galicia hives (NW Spain)

The botanic origin and the protein content of 15 honeys from small bee farms exploitations of Galicia, for family consume, were studied; the aim is to check if the protein wealth and the pollen wealth are dependent parameters. Seven honeys resulted to be Rhamnus frangula unifloral (pollen patterns with low diversity), two Castanea sativa Miller unifloral, other one heather unifloral, and five was multifloral honeys of various pollen patterns (four Castanea predominant and one Rhamnus frangula predominant). Their pollen wealth was low; eight honeys classified in the Maurizio Class I, 3 in Class II, 2 in Class III, and one in Maurizio Class IV. There has been a wide variability in its protein content (0.09- 4.83 mg prot./g honey). The relative amount of pollen from different taxa has a direct or inverse proportionality to wealth protein.

Subwavelength resolution for horizontal and vertical polarization by coupled arrays of oblate nanoellipsoids

A structure comprising a coupled pair of two-dimensional arrays of oblate plasmonic nanoellipsoids in a dielectric host medium is proposed as a superlens in the optical domain for both horizontal and vertical polarizations. By means of simulations it is demonstrated that a structure formed by silver nanoellipsoids is capable of restoring subwavelength features of the object for both polarizations at distances larger than half wavelength. The bandwidth of subwavelength resolution is in all cases very large (above 13%). (C) 2009 Optical Society of America

Carbon Isotopic Fractionation of CFCs during Abiotic and Biotic Degradation

Carbon stable isotope ((13)C) fractionation in chlorofluorocarbon (CFC) compounds arising from abiotic (chemical) degradation using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 °C) for CFC-113 and CFC-11 using ZVI show quantitative degradation of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (t(1/2)) of 20.5 h, and a ZVI surface-area normalized rate constant (k(SA)) of -(9.8 ± 0.5) × 10(-5) L m(-2) h(-1). CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to t(1/2) = 17.3 h and k(SA) = -(1.2 ± 0.5) × 10(-4) L m(-2) h(-1). Significant kinetic isotope effects of e(‰) = -5.0 ± 0.3 (CFC-113) and -17.8 ± 4.8 (CFC-11) were observed. Compound-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degradation and isotopic fractionation in LFG production, and local atmospheric impact of landfill emissions through the cover. Isotopic fractionations of ?(13)C ~ -13‰ (HCFC-22), ?(13)C ~ -35‰ (CFC-12) and ?(13)C ~ -15‰ (CFC-11) were observed for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope effect for (abiotic) ZVI degradation.

Variation in stable carbon isotope fractionation during aerobic degradation of phenol and benzoate by contaminant degrading bacteria

Variation in the natural abundance stable carbon isotope composition of respired CO2 and biomass has been measured for two types of aerobic bacteria found in contaminated land sites. Pseudomonas putida strain NCIMB 10015 was cultured on phenol and benzoate and Rhodococcus sp. I-1 was cultured on phenol. Results indicate that aerobic isotope fractionations of differing magnitudes occur during aerobic biodegradation of these substrates with an isotopic depletion in the CO2 (Delta(13)C(phenol-CO2)) as much as 3.7 parts per thousand and 5.6 parts per thousand for Pseudomonas putida and Rhodococcus sp. I-1 respectively. This observation has significant implications for the use of a stable isotope mass balance approach in monitoring degradation processes that rely on indigenous bacterial populations. The effects of the metabolic pathway utilised in degradation and inter-species variation on the magnitude of isotope fractionation are discussed. Possible explanations for the observed isotope fractionation include differences in the metabolic pathways utilised by the organisms and differences in specific growth rates and physiology. (C) 1999 Elsevier Science Ltd. All rights reserved.

Long-chain haloalkanes are incorporated into fatty-acids by Rhodococcus rhodochrous NCIMB-13064

The fatty acid composition of the cellular lipids of Rhodococcus rhodochrous NCIMB 13064 grown on various long-chain haloalkanes has been investigated and the influence of halogen substituents, carbon chain length and the position of halogen substitution in the growth substrate explored. Of the total fatty acids present in cells grown on 1-chloro-, 1-bromo- and 1-iodohexadecane, 75, 90 and 81%, respectively, were substituted in the omega-position by the corresponding halogen but only 1% of the fatty acids present after growth on 1-fluorotetradecane were fluorinated in this position. The extent of the halofatty acid incorporation with different halogen substituents in the growth substrate appears to reflect the degree to which oxygenase attack is restricted to the non-halogenated end of the haloalkane. Studies of the fatty acid composition of cells after growth on a series of 1-chloroalkanes containing an even number of carbon atoms between C-10 and C-18 indicated chlorofatty acid incorporation from C-12 to C-18 substrates at levels ranging from 21% with C-12 to 75% with C-16. The chlorofatty acids formed by initial oxidation of the chloroalkane were chain-lengthened or chain-shortened by from two to eight carbon atoms, with accompanying desaturation in some instances. Substantial quantities of a methyl-branched C-19:0 chlorofatty acid were also present with several chloroalkane substrates, When the fatty acid composition of cells after growth on 1-bromoalkanes containing an odd number of carbon atoms between C-11 and C-17 was examined, the incorporation of bromofatty acids was observed with C-13, C-15 and C-17 substrates; a maximum of 76% was recorded for the C-15 bromoalkane. As with even chain-length chloroalkanes, both chain-lengthening and -shortening occurred predominantly via two-carbon units so that most bromoacids present possessed an odd number of carbon atoms, When 1-bromododecane or 2-bromododecane were substrates, overall incorporations of bromofatty acids into the lipid fraction were very similar, demonstrating that the position of halogen substitution in the haloalkane was not critical in determining the extent of incorporation of the haloacids into cellular lipids. The results of the study indicate a mechanism by which degradation products of chlorinated paraffins could enter the biological food chain.

Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil

The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using (CO2)-C-13 pulse labelling, in an upland grassland ecosystem in Scotland. The use of C-13 enabled detection, in the field, of the effect of a 4-year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher delta(13)C% values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4-year period of liming indicated that the standing biomass was higher in plots that received lime. Lower delta(13)C% values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990-1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions.