INTERNAL EXPOSURE · in tissue equilibrium sampling to bridge the missing link between bioavailability and bioaccumulation

Internal exposure – in tissue equilibrium sampling to bridge the missing link between bioavailability and bioaccumulation

The central task addressed in INTERNAL EXPOSURE was to improve our understanding of the link between concentrations of organic contaminants in the marine environment and contaminant levels in the tissues of higher organisms where these chemicals can cause e.g. toxic effects. Passive equilibrium sampling, which is a relatively new approach, was used in this project: The sampler is a clean reference phase that is brought into contact with the medium of interest. The chemicals present in the medium diffuse towards the sampler that is retrieved after the establishment of equilibrium of the contaminants between the two phases. The sampler is then extracted and analysed for its content of pollutants. For this project, we chose an all-round polymer, the silicone rubber polydimethylsiloxane (PDMS), as the sampling phase. Polychlorinated biphenyls (PCBs) served as model chemicals due to their ubiquitous presence and ease of analysis. However, the results of INTERNAL EXPOSURE are applicable to a large range of pollutants with similar physicochemical properties. The passive equilibrium sampling approach can be seen as an environmental thermometer which assesses the status of different media. Instead of a temperature we obtain information about the chemical activity or 'escaping tendency' (i.e., fugacity) of contaminants, whether there will be diffusion from one medium to another etc. This kind of data is particularly valuable in a bioaccumulation context where differences in fugacities provide rapid information about whether a chemical is enriched in living organisms or not. The central task of INTERNAL EXPOSURE was worked on in the following areas: i) Is the sampling phase fit for purpose? In the beginning of the project, a common sampling material, the silicone rubber polydimethylsiloxane (PDMS) was chosen for all media to be studied within INTERNAL EXPOSURE. This ensured direct comparability of the concentrations of environmental pollutants in the PDMS at equilibrium as determined after equilibration in biota and the respective exposure medium (i.e., sediment or water). A study was carried out to test whether PDMS can be used in complex, challenging media, of which lipid-rich tissue is an example. In this context, a large variety of samples was tested, including more traditional matrices (sediment, suspensions of soil and humic substances) as well as complex, challenging matrices such as mayonnaise, meat, fish, olive oil and fish oil. The results showed that it was valid to use PDMS for passive equilibrium sampling in all tested matrices. ii) Development of methods for biota, water and sediment An in tissue equilibrium sampling method for fish was developed applying PDMS thin-films. The thin-films were inserted in intact fish tissue and retrieved after different times. After solvent extraction and a clean-up step, the extracts were analysed for PCBs. Regarding the exposure media of fish, a pilot study using PDMS in different types of samplers was carried out in Baltic Sea water. However, this study was not successful since some of the samplers could only partly be recovered or biological growth on the sampler surface disturbed the PCB measurements. Here we refer to the scientific literature for published methods on PDMS-based passive equilibrium sampling in water. INTERNAL EXPOSURE then focused on the development of a sampling method for Baltic Sea sediment. To this end, a published method applying glass vials that are PDMS-coated on the inner walls, developed for contaminated soil, was modified. For our application, 120 mL glass jars with very thin PDMS coatings (2 µm, 4 µm and 8 µm) on the inner vertical walls was successfully applied to Baltic Sea sediment. iii) Studies with biota In regular monitoring programs carried out in Sweden and many other countries, the responsible laboratories make use of traditional solvent-based total extraction of contaminants. In contrast to that approach, ... (attached document).

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