Gesine Witt

Polycyclic aromatic hydrocarbons (PAHs) in sediments of the Baltic Sea and of the German coastal waters

Abstract Samples of surface sediments (0–2 cm) and sediment cores (0–45 cm, 1 cm slices) were collected in the Belt Sea and Arkona Sea as well as in the internal and external coastal waters of Mecklenburg-Vorpommern. The concentrations of PAHs were analysed by HPLC and fluorescence detection. The results were verified by GUMS. The sum of PAHs varied between 11 ng/g dry weight for sandy sediments and 1900 ng/g for muddy sediments in the Belt Sea and Arkona Sea. Elevated concentrations up to 17000 ng/g were observed in the surface sediments of the internal coastal waters with highest concentrations in the Warnow estuary and in the Oder Haff. This indicates the significant contribution of river discharge to the contamination of sediments with PAHs. The distribution of the individual PAHs in sediments vary widely depending on their structure and molecular weight. The higher molecular 4 to 6 ring aromatics predominate due to their higher persistence. vertical profiles of PAH-concentrations are characterised by a maximum at depth between 1 cm and 8 cm and by an almost constant background level at depth below 22–24 cm. These patterns may be explained by changes in the anthropogenic release of PAHs. The sedimentological properties also affect the accumulation of PAHs. Strong correlations between concentrations of PAHs and the content of organic carbon could be established.

Passive sampling methods for contaminated sediments: Scientific rationale supporting use of freely dissolved concentrations

Passive sampling methods (PSMs) allow the quantification of the freely dissolved concentration (Cfree) of an organic contaminant even in complex matrices such as sediments. Cfree is directly related to a contaminants chemical activity, which drives spontaneous processes including diffusive uptake into benthic organisms and exchange with the overlying water column. Consequently, Cfree provides a more relevant dose metric than total sediment concentration. Recent developments in PSMs have significantly improved our ability to reliably measure even very low levels of Cfree. Application of PSMs in sediments is preferably conducted in the equilibrium regime, where freely dissolved concentrations in the sediment are well-linked to the measured concentration in the sampler via analyte-specific partition ratios. The equilibrium condition can then be assured by measuring a time series or a single time point using passive samplers with different surface to volume ratios. Sampling in the kinetic regime is also possible and generally involves the application of performance reference compounds for the calibration. Based on previous research on hydrophobic organic contaminants, it is concluded that Cfree allows a direct assessment of 1) contaminant exchange and equilibrium status between sediment and overlying water, 2) benthic bioaccumulation, and 3) potential toxicity to benthic organisms. Thus, the use of PSMs to measure Cfree provides an improved basis for the mechanistic understanding of fate and transport processes in sediments and has the potential to significantly improve risk assessment and management of contaminated sediments. Integr Environ Assess Manag 2014;10:197–209.

Matrix solid-phase microextraction for measuring freely dissolved concentrations and chemical activities of PAHs in sediment cores from the western Baltic Sea.

Sediment-pore water partitioning of polycyclic aromatic hydrocarbons (PAHs) was studied in sediment cores of a dumping area in the western Baltic Sea and compared to a reference site. Freely dissolved concentrations (C(free)) of nine PAHs were measured in sediment samples using solid-phase microextraction (SPME), a cost and time-efficient method with detection limits in the lower ng L(-1) range. Elevated levels of C(free) were measured at the dumping site, where concentration peaks in the core correlated with the presence of the dumped material, which was conspicuous in its color and consistency. Sediment concentrations of PAHs were three orders of magnitude higher at the dumping site than at the reference site, whereas C(free) was only one order of magnitude greater. Chemical activities of the PAHs in the sediment cores were calculated from C(free) to predict the baseline toxic potential of the contaminant mixture. Finally, gradients in C(free) and chemical activity were used to determine the direction of diffusion within the sediment and to obtain a spatial characterization of the PAH exposure. C(free) and chemical activity are important exposure parameters for the prediction of bioconcentration and toxicity in sediment organisms, and their measurement should be included in risk-assessment and pollution-management strategies.

Passive Equilibrium Sampler for in Situ Measurements of Freely Dissolved Concentrations of Hydrophobic Organic Chemicals in Sediments

In this study, an equilibrium passive sampling device is introduced that facilitates the in situ measurement of hydrophobic organic chemicals bioavailability in sediments in terms of freely dissolved concentrations. The new field sampler allows SPME fibers and silicone hollow fibers to be immersed and equilibrated in situ, whereas an automated liner exchanger (ALEX) facilitates the quantitative transfer of analytes to the GC without the use of extraction solvents. The sampler was developed for environmental monitoring as follows: (1) It is of very solid construction and can be reused practically ad infinitum. (2) Fibers with varying surface to volume ratios can be exposed in parallel in order to confirm that equilibrium was reached between sampler and sediment. (3) The equilibrium times allow a temporal resolution that is suited for monitoring of both long-term trends and seasonal effects. The automated thermal desorption reduced sample treatment to a minimum and ensured cost- and time-efficient measurements while minimizing potential error sources after the sampling. The sampler is applicable in a multitude of aquatic environments, especially where currents are low and sediments are muddy and well-mixed, e.g. by bioturbation. Examples for such environments are mud flats, harbor basins, river banks, and lakes.

Strategies for Transferring Mixtures of Organic Contaminants from Aquatic Environments into Bioassays

Mixtures of organic contaminants are ubiquitous in the environment. Depending on their persistence and physicochemical properties, individual chemicals that make up the mixture partition and distribute within the environment and might then jointly elicit toxicological effects. For the assessment and monitoring of such mixtures, a variety of cell-based in vitro and low-complexity in vivo bioassays based on algae, daphnids or fish embryos are available. A very important and sometimes unrecognized challenge is how to combine sampling, extraction and dosing to transfer the mixtures from the environment into bioassays, while conserving (or re-establishing) their chemical composition at adjustable levels for concentration-effect assessment. This article outlines various strategies for quantifiable transfer from environmental samples including water, sediment, and biota into bioassays using total extraction or polymer-based passive sampling combined with either solvent spiking or passive dosing.

Equilibrium passive sampling as a tool to study polycyclic aromatic hydrocarbons in Baltic Sea sediment pore-water systems.

Solid Phase Microextraction (SPME) was applied to provide the first large scale dataset of freely dissolved concentrations for 9 polycyclic aromatic hydrocarbons (PAHs) in Baltic Sea sediment cores. Polydimethylsiloxane (PDMS) coated glass fibers were used for ex-situ equilibrium sampling followed by automated thermal desorption and GC-MS analysis. From the PAH concentrations in the fiber coating we examined (i) spatially resolved freely dissolved PAH concentrations (Cfree); (ii) baseline toxicity potential on the basis of chemical activities (a); (iii) site specific mixture compositions; (iv) diffusion gradients at the sediment water interface and within the sediment cores and (v) site specific distribution ratios. Contamination levels were low in the northern Baltic Sea, moderate to elevated in the Baltic Proper and highest in the Gulf of Finland. Chemical activities were well below levels expected to cause narcosis to benthos organisms. The SPME method is a very sensitive tool that opens new possibilities for studying the PAHs at trace levels in marine environments.

Selected elements, PCBs, and PAHs in sediments of the North Sea—Baltic Sea transition zone: Sources and transport as derived from the distribution pattern

Abstract Geografisk Tidsskrift—Danish Journal of Geography 109(1):81–94, 2009 A total of 63 sediment samples were collected in the North Sea—Baltic Sea transition zone using hydraulically damped box-corer. Analysis of the top one cm sediments shows a north to south trend in Li, Ca and methylated PAHs suggesting transport of these elements and micro pollutants from the North Sea to the Baltic Sea. The sediment content of a high C/N ratio reflects preferential N decomposition during transport whereas a low P content in the northern and deepest part of the study area may result from early diagenesis effects. The spatial distributions of Zn and Pb with highest concentrations in the southern part of the study area imply local terrestrial supply and transport. In general, the PCB and PAH concentrations were high both in the northern and the southern parts of the area and low in-between. The relative constant ratio between the analyzed PCBs on all the stations suggests atmospheric deposition as the main source of PCB. Fluoranthene/Pyrene ratios >1 and Phenenthrene/Anthracene ratios <15 point at combustion of fossilfuel as the main source of PAH.

Assessing PCB pollution in the Baltic Sea - an equilibrium partitioning based study

Sediment cores and bottom water samples from across the Baltic Sea region were analyzed for freely dissolved concentrations (Cfree), total sediment concentrations (CT) and the dissolved aqueous fraction in water of seven indicator PCBs. Ex-situ equilibrium sampling of sediment samples was conducted with polydimethylsiloxane (PDMS) coated glass fibers that were analyzed by automated thermal desorption GC-MS, which yielded PCB concentrations in the fiber coating (CPDMS). Measurements of CPDMS and CT were then applied to determine (i) spatially resolved freely dissolved PCB concentrations; (ii) baseline toxicity potential based on chemical activities (a); (iii) site specific mixture compositions; (iv) diffusion gradients at the sediment water interface and within the sediment cores; and (vi) site specific distribution ratios (KD). The contamination levels were low in the Gulf of Finland and moderate to elevated in the Baltic Proper, with the highest levels observed in the western Baltic Sea. The SPME method has been demonstrated to be an appropriate and sensitive tool for area surveys presenting new opportunities to study the in-situ distribution and thermodynamics of hydrophobic organic chemicals at trace levels in marine environments.

Comparison of freely dissolved concentrations of PAHs in contaminated pot soils under saturated and unsaturated water conditions

Passive sampling (PS, equally used for passive sampler) methods have successfully been applied in situ to quantify the bioavailability of hydrophobic organic compounds in air, water and sediments. However, very little is known on the applicability of PS in unsaturated soils. Here, we present the results of a greenhouse experiment in which we applied in situ PS methods in pots. Low density polyethylene (LDPE) and polydimethylsiloxane (PDMS) fibres with a newly developed PS holder were used to analyse freely dissolved polycyclic aromatic hydrocarbon (PAH) concentrations (Cfree) in a skeet shooting range soil and an uncontaminated control soil under water saturated and unsaturated conditions for up to nine months. A short exposure time of three months was not sufficient for the PDMS samplers to reach distribution equilibrium with the surrounding soil. Under saturated water conditions, the in situ results agreed well with measurements obtained from the conventional ex situ soil suspension method. They were in accordance with similar comparisons made in previous studies on sediments, as well as with model predictions. However, for unsaturated water conditions, the results differed considerably from the ex situ Cfree values, in particular for the light molecular weight (LMW) PAHs such as phenanthrene, fluoranthene, and pyrene. The results of the two in situ PS methods were in good agreement with each other under both soil water conditions, indicating that dissipation mechanisms, such as degradation or volatilization, led to a substantial decrease in Cfree under unsaturated conditions, especially for the LMW PAHs (log10KOW < 5.85) over a period of six months or more. Thus, in their current state of development, in situ PS methods can be used in soils under water-saturated conditions. However, an adequate method to correct for non-equilibrium conditions needs to be developed before they can be applied to unsaturated conditions, mainly for LMW PAHs.

Equilibrium sampling of HOCs in sediments and suspended particulate matter of the Elbe River

BackgroundChemical quality of sediment and suspended particulate matter (SPM) is usually assessed by total chemical concentrations (Ctotal). However, the freely dissolved concentration (Cfree) is the ecologically more relevant parameter for bioavailability, diffusion and bioaccumulation. In recent studies, equilibrium sampling has been applied to determine Cfree of hydrophobic organic contaminants (HOCs) in the sediment pore water, whereas such data are missing for SPM. We applied solid-phase micro-extraction to measure and compare Cfree of PAHs and PCBs in pore water of sediments and SPM sampled along the German part of the river Elbe. Moreover, site-specific distribution ratios were evaluated and Cbio,lipid was predicted using Cfree.ResultsCfree of PAHs remained largely constant while Cfree of PCBs varied along the Elbe River. The highest Ctotal of PCBs and PAHs were found at Prossen (km 13) and Meißen (km 96). PCB Ctotal even exceeded the environmental quality standard for sediment and SPM in Prossen. Site-specific distribution ratios (KD) revealed a stronger sorption for PAHs compared to PCBs, indicating a higher availability of PCBs. Equilibrium partitioning concentrations in lipids (Clip↔sed) showed a high correlation with actually measured lipid-normalised concentrations (Cbio,lipid) in bream. This indicates that PCB bioaccumulation in this benthic fish species is closely linked to the sediment contamination.ConclusionsIn rivers, SPM functions as a transportation vehicle for HOCs along the stream until it eventually deposits to the sediment. This study demonstrates that due to weaker sorption of PAHs and PCBs to the SPM this matrix poses a higher risk to the aquatic environment compared to the sediment. The prediction of Cbio,lipid of PCBs was correct and shows that solid-phase micro-extraction is highly suited to predict lipid concentration, and thus a valuable tool for risk-assessment or sediment management.