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.     

Nest separation and the dynamics of the Gestalt odor in the polydomous ant Cataglyphis iberica (Hymenoptera, Formicidae)

In the polydomous ant species Cataglyphis iberica, nests belonging to the same colony are completely separated during hibernation. In order to examine whether this separation induces changes both in the hydrocarbon profile and in recognition ability between adult nestmates, we separated groups of workers for several months under two different conditions: at hibernation temperature and at room temperature. At room temperature, recognition remained unchanged but separation led to longer mutual antennations relative to non-separated controls. When half of a colony was placed under hibernation conditions, antennal interactions also increased in duration and a few aggressive interactions emerged between separated ants. This aggressiveness never reached the intercolonial level observed in this species. In both cases, the hydrocarbon profiles showed differences between individuals after separation while remaining homogeneous within each nest. This chemical modification may induce the longer antennations observed. After separated groups were reunited, individuals recovered their previous antennation pattern and a convergence in hydrocarbon profiles was again observed. These concurrent observations suggest that hydrocarbons are transferred between nestmates. In C. iberica, the formation of the colonial odor seems to follow the “Gestalt” model which allows all satellite nests of a colony to have a common colonial odor. In the field, temporary nest isolation during hibernation may induce divergence between satellites. The role of adult transport in connecting nests during the active season to obtain an efficient Gestalt odor is discussed. Received: 16 June 1997 / Accepted after revision: 25 October 1997     

Sediment-associated aliphatic and aromatic hydrocarbons in coastal British Columbia, Canada: concentrations, composition, and associated risks to protected sea otters

Sediment-associated hydrocarbons can pose a risk to wildlife that rely on benthic marine food webs. We measured hydrocarbons in sediments from the habitat of protected sea otters in coastal British Columbia, Canada. Alkane concentrations were dominated by higher odd-chain n-alkanes at all sites, indicating terrestrial plant inputs. While remote sites were dominated by petrogenic polycyclic aromatic hydrocarbons (PAHs), small harbour sites within sea otter habitat and sites from an urban reference area reflected weathered petroleum and biomass and fossil fuel combustion. The partitioning of hydrocarbons between sediments and adjacent food webs provides an important exposure route for sea otters, as they consume ∼25% of their body weight per day in benthic invertebrates. Thus, exceedences of PAH sediment quality guidelines designed to protect aquatic biota at 20% of the sites in sea otter habitat suggest that sea otters are vulnerable to hydrocarbon contamination even in the absence of catastrophic oil spills.     

水中痕量多环芳烃(PAHs)类环境污染物检测方法的研究

对水中多环芳烃（ＰＡＨｓ）检测方法进行了系统研究，采用固相萃取技术进行样品前处理，以取代传统的液液萃取，并建立了优化的ＰＡＨｓ液相色谱分析条件，可以适用于美国ＥＰＡ优先监控的水中１６种ＰＡＨｓ的同时分析