Two fish bile reference materials certified for PAH metabolites

Environmental pollution with polycyclic aromatic hydrocarbons (PAHs) from pyrogenic or petrochemical sources is a matter of concern in many aquatic ecosystems. For field monitoring purposes, PAH metabolite levels in fish bile samples can be used as biomarkers of exposure, but previously there were no reference materials for analytical method validation or quality control. In this paper we describe the preparation and certification of two fish bile materials. BCR 720 is a pure bile material from sediment-exposed flounder (Platichthys flesus) and BCR 721 is a pure bile material from oil-exposed plaice (Pleuronectes platessa). Homogeneity and stability tests were carried out and a group of 12 expert laboratories was assembled for the certification measurements. The methods applied were liquid chromatography with fluorescence detection or gas chromatography with mass spectrometric detection. In BCR 720 three PAH metabolites were certified: 1-hydroxyphenanthrene, 1-hydroxypyrene and 3-hydroxybenzo[a]pyrene. In BCR 721 1-hydroxypyrene was certified. The fourth target compound, 2-hydroxynaphthalene, could not be certified, but the results obtained are listed. The major findings from earlier feasibility studies and recommendations for the optimal use of the reference materials are also included.     

Moisture monitoring in waste disposal surface barriers

Surface barriers for waste disposal sites should preventwaste water and gas emission into the environment. It isnecessary to assess their proper operation by monitoring thewater regime of the containment. A set of three new water contentmeasuring devices has been developed that provide an economicalsolution for monitoring the moisture distribution and waterdynamic. They will give an early warning service if the barriersystem is at risk of being damaged. The cryo soil moisture sensor`LUMBRICUS' is an in situ self-calibrating absolute water contentmeasuring device. It measures moisture profiles at spot locationsdown to 2.5 m depth with an accuracy of better than 1.5% and adepth resolution of 0.03 m. The sensor inherently measuresdensity changes and initial cracks of shrinking materials likeclay minerals. The large area soil moisture sensor `TAUPE' is amoisture sensitive electric cable network to be buried in themineral barrier material of the cover. A report will be givenwith results and experiences on an exemplary installation at theWaste Disposal Facility Karlsruhe-West. 800 m² of the barrierconstruction have been continuously monitored since December1997. Volumetric water content differences of 1.5% have beendetected and localised within 4 m. This device is alreadyinstalled in two other waste disposal sites. A modified `TAUPE'was constructed for the control of tunnels and river dams aswell. Thin sheet moisture sensor `FORMI' is specifically designedfor moisture measurements in liners like bentonite, textile andplastic. Due to its flexibility it follows the curvature of theliner. The sensor measures independently from neighbouringmaterials and can be matched to a wide range of differentthickness of the material. The sensors are patented in several countries.     

Effect of corona discharge on the gas composition of the sample flow in a Gas Particle Partitioner

A Gas Particle Partitioner (GPP) that allows highly efficient separation of gas and particles with no effect on the thermodynamic conditions and substantially no change of the gas composition has been developed. The GPP is a coaxial arrangement with inner and outer electrodes and utilizes a corona discharge to electrically charge the particles and a strong electric field to remove them from the sample flow. Several measures were taken to avoid an influence of the corona discharge on the gas composition. The GPP can be applied for various applications. This paper focuses on the use of the GPP as a pre-filter for gas analyzers, where zero pressure drop and a minimization of the influence of the corona discharge on the gas composition are the main objective. Due to its design, the GPP introduces no changes to the thermodynamic conditions. However, corona discharge is known to produce significant amounts of ozone and oxides of nitrogen. The effect of the corona on the gas composition of the sample flow was determined under various conditions. The gas concentrations strongly depended on several aspects, such as material and diameter of the corona wire and polarity of the corona voltage. Due to the measures taken to minimize an effect on the gas composition, the concentrations of these gases could effectively be reduced. Along with the maximum gas-particle separation efficiency of near 100%, the additional O3 concentration was 42 ppbV and the additional NO2 concentration 15 ppbV. If an efficiency of 95% is acceptable, the added concentrations can be as low as 2.5 ppbV (O3) and 0.5 ppbV (NO2), respectively.     

An evaluation of two fluorescence screening methods for the determination of chrysene metabolites in fish bile

Two screening methods, synchronous fluorescence spectrometry (SFS) and high performance liquid chromatography with fluorescence detection (HPLC-F), have been evaluated for their suitability in determining chrysene metabolites in fish bile. The optimal wavelength pair, excitation/emission 272/374 nm, for SFS measurements of chrysene metabolites was identified by analysis of bile taken from fish exposed to the pure compound. This analysis revealed in addition some information about the metabolite pattern. However, when bile from fish exposed to complex and environmentally relevant mixtures of polycyclic aromatic hydrocarbons (PAHs) was analysed using these methods, identification of the chrysene metabolites was poor. Analysis of bile taken from fish exposed to single PAHs identified other three- and four-ring aromatics as the main interfering compounds. Both methods were equally able to discriminate between impacted and reference sites by determination of relative concentrations of fluorescent three- and four-ring aromatics.     

Long-range transport potential of semivolatile organic chemicals in coupled air-water systems

Ongoing deliberations on the regulation of semivolatile organic chemicals require the assessment of chemical transport in atmospheric and marine systems. The characteristic travel distance was proposed as a measure for the transport potential in air and water. However, the existing definition treats the transport processes separately. It is shown that combined transport in coupled air-ocean systems can accelerate the overall transport into remote regions. Concentration ratios in air and water change with distance from sources depending on the initial concentration ratio and on the difference between the transport velocities. A measure is suggested facilitating the chemical screening with respect to transport potentials in such air-ocean systems. A case study for alpha and gamma-hexachlorocyclohexane shows that the suggested measure qualitatively reveals the transport potentials of these chemicals and exemplifies possible concentration patterns.     

A mesoscale vortex in a small stratified lake

A mesoscale vortex structure in the small stratified Lake Stechlin has been revealed by field experiments with satellite-tracked quasi-lagrangian drifters. The vortex with a radius of about 200 m drifted at 300 m/day along the western bight of the lake with nearly constant rotation speed of 3 cpd. Analysis of kinematical properties of the vortex motion demonstrates solid body character of rotation. Extrapolation of the vortex drift trajectory over the period preceding the observations combined with data on local winds and seiche dynamics has allowed tracing the vortex fate from its generation point. The normal modes analysis of the internal seiching in the lake reveals the vortex generation mechanism to be the interaction of certain seiche modes with local bottom topography and suggests generation of the mesoscale vortices to be the a regular feature of the lake circulation. Analysis of vorticity suggests additional energy supply to rotational flow, possibly from inverse cascading of small-scale turbulent motions—a feature typical for quasi-2D turbulence. The vortices can play an important role in the energy transport from basin-scale motions to small-scale boundary mixing. They can also contribute significantly to the horizontal heterogeneity of phyto- and zooplankton distribution as well as to the transport of dissolved matter such as nutrients between littoral and profundal areas. The topographically generated traveling vortices represent an analog of the synoptic eddies in the Ocean and in the Atmosphere, whereas their role in the lake hydrodynamics is practically unknown.     

Application and test of a simple tool for operational footprint evaluations

We present a user-friendly tool for footprint calculations of flux measurements in the surface layer. The calculations are based on the analytical footprint model by Kormann, R. and Meixner, F.X. [2001. An analytical footprint model for Non-neutral Stratification. Boundary-Layer Meteorology 99, 207-224]. The footprint density function of a flux sensor is determined using readily available data from standard eddy covariance measurements. This footprint density function is integrated over defined surface areas given as quadrangular polygons representing e.g. agricultural fields. We illustrate the use and performance of the tool by applying it to CO2 flux measurements with three eddy covariance system at the Swiss CarboEurope grassland site. Two flux towers were positioned in the centre of two neighbouring fields, respectively, that showed a very different CO2 flux during the study period. The third tower was located near the border of the two fields and was frequently influenced by both fields to a similar degree. The calculated footprint fractions were used to simulate the latter flux from the other two systems. The measured and simulated fluxes showed a good agreement and thus support the reliability of the footprint calculation. The presented simple footprint tool can be used as a routine quality check for flux monitoring stations influenced by surface areas with varying vegetation covers and/or land-use.     

Uncertainty assessment of contaminant plume length estimates in heterogeneous aquifers

The Virtual Aquifer approach is used in this study to assess the uncertainty involved in the estimation of contaminant plume lengths in heterogeneous aquifers. Contaminant plumes in heterogeneous two-dimensional conductivity fields and subject to first order and Michaelis-Menten (MM) degradation kinetics are investigated by the center line method. First order degradation rates and plume lengths are estimated from point information obtained along the plume center line. Results from a Monte-Carlo investigation show that the estimated rate constant is highly uncertain and biased towards overly high values. Uncertainty and bias amplify with increasing heterogeneity up to maximum values of one order of magnitude. Calculated plume lengths reflect this uncertainty and bias. On average, plume lengths are estimated to about 50% of the true plume length. When plumes subject to MM degradation kinetics are investigated by using a first order rate law, an additional error is introduced and uncertainty as well as bias increase, causing plume length estimates to be less than 40% of the true length. For plumes with MM degradation kinetics, therefore, a regression approach is used which allows the determination of the MM parameters from center line data. Rate parameters are overestimated by a factor of two on average, while plume length estimates are about 80% of the true length. Plume lengths calculated using the MM parameters are thus closer to the correct length, as compared to the first order approximation. This approach is therefore recommended if field data collected along the center line of a plume give evidence of MM kinetics.