Bioconcentration of n-dodecane and its highly branched isomer 2,2,4,6,6-pentamethylheptane in fathead minnows

Petroleum products are complex mixtures of hydrocarbons. They are important as constituents of fuels and lubricants, and as key raw materials for the chemicals industry. Since there is a potential for accidental releases to the aquatic environment, bioaccumulation of higher hydrocarbons is of concern. Here, the bioconcentration behaviour of two representative hydrocarbons, the dodecane isomers n-dodecane and 2,2,4,6,6-pentamethylheptane (PMH), was investigated in fathead minnows at concentrations in water below their maximum aqueous solubility. The concentration of n-dodecane in fish did not exceed our method limit of detection of 60 μg/kg. In contrast, PMH could be quantified in fish. No significant increase in the ratio of PMH concentrations in fish to water could be detected indicating that an exposure time of 4–10 days is sufficient to approach steady-state. For n-dodecane the upper limit of the bioconcentration factor (BCF) is estimated by dividing the method limit of detection by the exposure concentration and a value of 240 l/kg is derived. For PMH the bioconcentration factor, estimated as the average fish/water concentration ratio during the steady-state part of the experiment, ranges between 880 and 3500 l/kg. The BCFs of both compounds are small compared to their hydrophobicity. Given that both linear and branched hydrocarbons are known to be biotransformed by fish, it appears that efficient metabolism of the test compounds in fathead minnows prevents bioaccumulation.     

Modelling biodegradation of hydrocarbons in aquifers: when is the use of the instantaneous reaction approximation justified?

In-situ bio-remediation is a viable cleanup alternative for aquifers contaminated by hydrocarbons such as BTEX. Transport models of varying complexity and capabilities are used to quantify their degradation. A model that has gained wide acceptance in applications is BIOPLUME II, which assumes that oxygen-limited biodegradation takes place as an instantaneous reaction. In this work we have employed theoretical analysis, using non-dimensional variables, and numerical modelling to establish a quantitative criterion demarcating the range of validity of the instantaneous reaction approximation against biodegradation kinetics. Oxygen was the limiting species and sorption was ignored. This criterion relates (o), the Dahmk?hler number at oxygen depletion, to O(o)*, the ratio of initial to input oxygen concentration, (o) > or = 0.7(O(o)*)(2) + 0.1O(o)* + 1.8. The derived (o) reflects the intrinsic characteristics of the physical transport and of the biochemical reaction, including the effect of biomass density. Relative availability of oxygen and hydrocarbons exerts a small influence on results. Theory, verified and refined via numerical simulations, showed that significant deviations of instantaneous reactions from kinetics are to be expected in the space-time region s相似文献   

Composition of extractable organic matter in aerosols from urban areas of Rio de Janeiro city, Brazil

The hydrocarbon compositions of atmospheric particulate matter from urban areas of Rio de Janeiro city have been studied to assess the different pollution levels. Samples were acquired using a standard high-volume air sampler (Hi-Vol), extracts were prepared and fractionated into aliphatic and aromatic compounds. High-resolution gas chromatography and GC coupled to mass spectrometry (GC–MS) were used for the analysis of the organic matter. The results show that all samples contain n-alkanes, but the distributions are different for each sample, reflecting both the biogenic (vascular plant wax input) and fossil fuel contamination sources (vehicular exhaust). The fossil fuel biomarkers, hopanes and steranes, were also observed in all samples except in the Tijuca Forest, which is a mountain forest in the midst of the sea-level city. A decrease in the level of pollution was observed in the sequence for Rebouças Tunnel>Cinelândia (downtown)>Quinta da Boa Vista Park>Tijuca Forest, as expected from the traffic density. Unfortunately, all sites are polluted mainly from vehicular emissions, but at different degrees, with the lowest levels in Tijuca Forest.     

Vertical infiltration of fuel oil hydrocarbons in an agricultural soil

The influence of rainfall, air temperature and soil moisture on the vertical mobility in the soil of fuel oil hydrocarbons (HC) was investigated in a field experiment. A controlled spreading of fuel oil (nC10‐nC25) was performed at a rate of 5 L HCm^‐2 on an agricultural soil in summer and in winter. Concentration, chemical composition of HC and soil moisture were regularly determined at different soil depths between 0 and 140 cm, 1 h, 3, 8and 15 days (d) after the spreading of oil. Sorption of hydrocarbons onto the organo‐mineral matrix of the soil was studied in laboratory experiments. The results showed that in summer, with an air temperature of 24°C and without water leaching in the soil profile, 65% of the initial HC remained trapped in the 0–140 cm soil layer, about 20% of the HC volatilized and around 15% migrated deeper. A vertical selective migration of the lightest (nC10‐nC15) HC (naphthas) was shown lSd after the spreading of fuel oil. Naphthas progressively reached the 120–140 cm soil layers whereas the heavy fractions of oil (nC17‐nC25) migrated and concentrated in the 0–60 cm soil layers. In winter, when soil was regularly watered by rainfalls and at low air temperatures, only 47% of the initial HC remained in the 0–140 cm profile after 15 d. A fast vertical infiltration of naphthas occurred within the first 3 d. After 15 d, all HC were detected in the same relative amounts as in the initial oil in the whole profile. Volatilization was negligible in winter and an increase in the migration of total oil at depth in the soil profile was shown. As inferred from the laboratory experiments, the high soil moisture led to the decrease in HC sorption on the organo‐mineral matter of the soil.     

The impact of natural and anthropogenic hydrocarbons on the tropospheric budget of carbon monoxide

A method to quantify the relative contributions of surface sources and photochemical production of atmospheric carbon monoxide has been implemented in a three-dimensional chemical-transport model. The impact of biogenic and anthropogenic hydrocarbons has been calculated. The oxidation of isoprene contributes to about 10% of the global tropospheric burden of carbon monoxide, with a maximum contribution over southern America and Africa. Oxidation of methane and terpenes contribute to 28 and 2%, respectively, of the tropospheric burden of CO. The oxidation of the other hydrocarbons, which include ethane, propane, ethylene, propylene and the surrogate hydrocarbon representing other hydrocarbons results in 12% of the CO tropospheric burden, among which 69% results from the oxidation of hydrocarbons of biologic origin. The overall global CO yield from the oxidation of isoprene is estimated to be 23% on a carbon basis. Comparisons between model results and the few available observations of isoprene, terpenes and their oxidation products show that there is no evidence that the current global isoprene emissions proposed in the IGAC/GEIA emissions data base are substantially overestimated, as suggested by previous studies.     

土壤石油烃类污染治理方法述评

本文介绍了土壤中石油烃类的危害，在土壤中的主要存在形态及迁移转化情况；概述了近年来国内外治理土壤石油烃类污染和各种方法，并从场外治理和现场治理两个角度分别对各种物理、化学和生物治理方法的优缺点、可行性进行了述评；同时对联合运用多种技术，实行综合治理进行了讨论．     

Epicuticular wax of large and small white butterflies,<Emphasis Type="Italic"> Pieris brassicae</Emphasis> and<Emphasis Type="Italic"> P. rapae crucivora</Emphasis>: qualitative and quantitative comparison between diapause and non-diapause pupae

We compared the quantity and quality of the epicuticular wax of diapause and non-diapause pupae in two closely related Pieris species, P. brassicae and P. rapae crucivora. Main components of their epicuticular wax were identified as hydrocarbons. In P. brassicae, more than 95% of hydrocarbons were saturated regardless of whether the pupae were in diapause or not. In P. rapae crucivora, 93% of hydrocarbons were saturated in non-diapause pupae whereas in diapause pupae 41% were saturated and 59% unsaturated. From measurements of body surface area by nuclear magnetic resonance microimaging, we calculated the average thickness of the wax layer. The thickness in diapause and non-diapause pupae of P. brassicae was 800 and 160 nm, respectively. In P. rapae crucivora, the thickness was 195 nm in diapause and 11 nm in non-diapause. This is the first report to clarify the compositional difference in epicuticular wax between diapause and non-diapause pupae.     

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o-xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m,p-xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o-xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable.     

双柱双检测器气相色谱法同时进样分析非甲烷烃

介绍了用双柱双氢火焰离子化检测器同时进样气相色谱法分析气体样品中非甲烷烃.经过与现有方法的比较,该方法具有平行性更好、数据更准确、分析速度快等优点,各项指标均大大优于现行标准HJ/T 38-1999中的数据.通过软硬件的改进,解决了以前非甲烷烃在分析中由于在时间上所引起的数据倒置、分析误差等问题.     

不同土地利用类型作物中多环芳烃含量调查

文章调查了江苏苏州某典型生态示范区内,多环芳烃在不同土地利用类型和各种作物的富集、迁移、转化情况并进行比对、分析,确定不同土地利用类型中作物多环芳烃污染水平不同;不同作物对多环芳烃的富集效率不同;同一作物的不同组织(器官)多环芳烃含量也不同,初步分析了多环芳烃在水-土-气各介质之间的迁移富集规律.为推进江苏"生态省"建设与可持续发展提供一定的技术参考依据.