Hydrochemical and isotopic effects associated with petroleum fuel biodegradation pathways in a chalk aquifer

Hydrochemical data, compound specific carbon isotope analysis and isotopic enrichment trends in dissolved hydrocarbons and residual electron acceptors have been used to deduce BTEX and MTBE degradation pathways in a fractured chalk aquifer. BTEX compounds are mineralised sequentially within specific redox environments, with changes in electron acceptor utilisation being defined by the exhaustion of specific BTEX components. A zone of oxygen and nitrate exhaustion extends approximately 100 m downstream from the plume source, with residual sulphate, toluene, ethylbenzene and xylene. Within this zone complete removal of the TEX components occurs by bacterial sulphate reduction, with sulphur and oxygen isotopic enrichment of residual sulphate (epsilon(s) = -14.4 per thousand to -16.0 per thousand). Towards the plume margins and at greater distance along the plume flow path nitrate concentrations increase with delta15N values of up to +40 per thousand indicating extensive denitrification. Benzene and MTBE persist into the denitrification zone, with carbon isotope enrichment of benzene indicating biodegradation along the flow path. A Rayleigh kinetic isotope enrichment model for 13C-enrichment of residual benzene gives an apparent epsilon value of -0.66 per thousand. MTBE shows no significant isotopic enrichment (delta13C = -29.3 per thousand to -30.7 per thousand) and is isotopically similar to a refinery sample (delta13C = -30.1 per thousand). No significant isotopic variation in dissolved MTBE implies that either the magnitude of any biodegradation-induced isotopic fractionation is small, or that relatively little degradation has taken place in the presence of BTEX hydrocarbons. It is possible, however, that MTBE degradation occurs under aerobic conditions in the absence of BTEX since no groundwater samples were taken with co-existing MTBE and oxygen. Low benzene delta13C values are correlated with high sulphate delta34S, indicating that little benzene degradation has occurred in the sulphate reduction zone. Benzene degradation may be associated with denitrification since increased benzene delta13C is associated with increased delta15N in residual nitrate. Re-supply of electron acceptors by diffusion from the matrix into fractures and dispersive mixing is an important constraint on degradation rates and natural attenuation capacity in this dual-porosity aquifer.     

Correlation of gas chromatographic properties of chlorobenzenes and polychlorinated biphenyls with the occurrence of reductive dechlorination by untamed microorganisms

To understand the dechlorination ability of chlorobenzenes (CBs) and polychlorinated biphenyls (PCBs) by untamed microorganisms under anaerobic condition and to correlate gas chromatographic properties with the occurrence of reductive dechlorination, introduction of CBs and PCBs in the culture medium inoculated with microorganisms from sludge and sediment, respectively, were performed. Three kinds of culture media preparing from sludge, river water and a synthetic medium were used in the experiments. HCB was degraded to 1,3,5-trichlorobenzene (1,3,5-TCB) and 1,3-dichlorobenzene (1,3-DCB) in both sludge medium and synthetic medium with inoculated microorganisms. Three PCB congeners including 2,3,4-, 3,4,5- and 2,3,4,5-CBp (chlorinated biphenyl) were not found to be dechlorinated in the river water medium with inoculation culture but to be dechlorinated in the synthetic medium. MNDO methodology was used to compute theoretical dechlorination reaction heats and GC-ECD techniques were used to estimate chromatographic data of CB and PCB congeners. Both CB and PCB congeners showed that dechlorination by untamed microorganisms under anaerobic mixed cultures were more likely to occur when larger amounts of energy were released and greater deltaln RRT value between the parent congener and the daughter product was observed. Deltaln RRT provided a more precise information on the singularity of PCBs ortho-dechlorination in an aspect of thermodynamic favorable rule.     

One-dimensional simulation of solute transfer in saturated-unsaturated porous media using the discontinuous finite elements method

A one-dimensional transport model for simulating water flow and solute transport in homogeneous-heterogeneous, saturated-unsaturated porous media is presented. The model is composed of a combination of accurate numerical algorithms for solving the nonlinear Richard's and advection-dispersion equations (ADE). The mixed form of Richard's equation is solved using a standard finite element method (FEM) with primary variable switching. The transport equation is solved using operator splitting, with the discontinuous finite element method (DFE) for discretization of the advective term. A slope limiting procedure for DFE avoids numerical instabilities but creates very limited numerical dispersion for high Peclet numbers. An implicit finite differences scheme (FD) is used for the dispersive term. The unsaturated flow and transport model (Wamos-T) is applied to a variety of rigorous problems including transient flow, heterogeneous medium and abrupt variations of velocity in magnitude and direction due to time-varying boundary conditions. It produces accurate and mass-conservative solutions for a very large range of grid Peclet numbers. The Wamos-T model is a good and robust alternative for the simulation of mass transport in unsaturated domain.     

Weekday/weekend differences in OH reactivity with VOCs and CO in Baltimore, Maryland

This study compared the first-order frequencies for OH associated with volatile organic compounds (VOCs) and CO (hereafter called OH reactivity with VOCs or CO), the product of the VOC or CO concentration, and their respective kOH value, on an average weekday with that on an average weekend day at a core urban site in Baltimore, MD. The average daytime concentrations were calculated for each of the 55 available Photochemical Assessment Monitoring Station (PAMS) VOCs using data from the Baltimore site. The data were sorted in descending order to highlight the important species based on concentration. The OH reactivity with VOCs was sorted in descending order to identify the important species based on the magnitude of the OH reactivity. A similar process was followed for the OH reactivity with CO. The contribution of the significant species to the weekday/weekend difference in OH reactivity was examined. The OH reactivity with C5H8 was the largest among the OH reactivity with the PAMS' VOCs and was the same on the weekday and weekend. The weekday/weekend difference in OH reactivity with VOCs was entirely due to differences in concentrations of the anthropogenic VOCs. The OH reactivity with VOCs was 11% larger on the weekday. When OH reactivity with CO was included, the OH reactivity was 13% larger on the weekday.     

PCDDs, PCDFs, PCBs and HCB in marine and estuarine sediments from Queensland, Australia.

Concentrations of 2,3,7,8-chlorine substituted PCDDs, PCDFs, selected PCB congeners and HCB were determined in sediment samples collected from sites along the east coast of Queensland in northern Australia. PCDDs were detectable in all sediment samples while PCDFs, PCBs and HCB were mainly found in sediment samples collected from sites in the Brisbane metropolitan area. The results provide evidence that an unidentified source for higher chlorinated PCDDs exists along the Queensland coast.     

The utilization of the Antarctic environmental specimen bank (BCAA) in monitoring Cd and Hg in an Antarctic coastal area in Terra Nova Bay (Ross Sea--Northern Victoria Land)

The first projects relating to levels of Cd and Hg on marine biota and sediments from Terra Nova Bay (Ross Sea--Antarctica) and their bioaccumulation and biomagnification in this trophic web have been carried out by research programmes pertaining to the Italian Antarctic Research Program (PNRA) since 1989. Making use of this data, and checking the same metals after 10 years thanks to the samples stored in the BCAA, we have looked for the levels of Cd and Hg in a coastal marine ecosystem of Terra Nova Bay, and have proposed using some organisms to monitor the levels of these two heavy metals in this environment where the Italian Base is located, using the data determinate in this work as background levels. In our work, the amount of Hg and Cd concentrations have been determined in biota from the inner shelf of Terra Nova Bay (Adamussium colbecki, Laternula elliptica, Odontaster validus, Sterechinus neumayeri, Trematomus bernacchii, Iridaea cordata, Phyllophora antarctica, Parborlasia corrugatus), and in two different size fractions of sieved marine sediments (<2000 microm and <63 microm). To widen the distribution of Cd and Hg in this ecosystem we have also investigated the fraction of these metals bound to the labile phase of the marine sediments, and their presence in the particulate matter found in pack-ice cores, recent snow, water column and sea microlayer.     

Analysis of nitrated polynuclear aromatic hydrocarbons

A derivatization-gas chromatography/electron capture detector (GC/ECD) method has been developed for the measurement of trace nitrated polynuclear aromatic hydrocarbons (NPAHs) in air. The method involves first the derivatization of parent nitro-PAHs to their corresponding fluorinated derivatives, followed by GC/ECD analysis. The sensitivity of the method is an order of magnitude higher than those of direct GC/ECD analysis of NPAHs themselves. The method is simple and robust and thus ideally suited for the routine monitoring of NPAHs in air samples. The sensitivity and reproducibility of GC/negative ion chemical ionization MS (NICIMS) for the measurement of NPAHs after derivatization has been evaluated. The method has sensitivity comparable to GC/ECD, but is less reproducible in quantification. The method is therefore suitable for method validation and NPAHs peak confirmation rather than routine operations.     

Chemical fingerprinting applied to the evaluation of marine oil pollution in the coasts of Canary Islands (Spain)

Chemical fingerprinting approach to environmental assessment is illustrated in the evaluation of marine oil pollution in the coasts using two limpet species as bioindicator organisms, and based on profiles and concentrations of n-alkanes and aromatic hydrocarbons in their tissues. Accidental and chronic releases of hydrocarbons can contaminate the marine environment of the Canary Islands not only because of their geographical situation but also because of the very dense tanker traffic around. This situation affects coastal areas, fishing activities, tourism resort, etc. Concentrations of n-alkanes and aromatic hydrocarbons (polycyclic aromatic hydrocarbons and methyl-polycyclic aromatic hydrocarbons) in the soft tissues of the marine intertidal and subtidal limpets, Patella crenata and Patella ullysiponensis aspera, were evaluated. Limpet samples were collected at monthly intervals, at three locations on the southeast coast of Tenerife over a 3-year period (1991-93). Levels of hydrocarbons found in limpets are similar to concentrations found in unpolluted areas around the world. From application of principal component analysis, the interpretation of variable loading plots gives information on variable correlation and can be used to distinguish among potential sources of pollution and the ability of studied molluscs to be used as bioindicator organisms.     

The environmental impact of shrimp aquaculture: a global perspective

A global perspective on the environmental impacts related to the establishment and operation of shrimp aquaculture is presented. Alternatives to reduce the impacts are considered and research priorities are recommended.