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The development of industrial processes in the 19^th and 20^th centuries, in particular oil refining, resulted in a huge discovery and subsequent large-scale production of a variety of chemicals. These useful chemicals supposedly made the everyday lives of people easier and better by, for instance, controlling the spread of diseases such as malaria, through the use of DDT and other organochlorine pesticides (OCPs).

During the 1970s and following decades, it was hypothesized and later shown, that these, and other “helpful chemicals” such as polychlorinated biphenyls (PCBs), played a crucial role in the steep population decline observed for multiple species in the Baltic Sea. They were classified as anthropogenic (man-made) hazardous substances (AHSs). Many AHSs can be stored in fatty tissues of the organisms and magnify in species at high trophic levels (predators) of the food web, as a result of persistence and transfer from lower-level organisms (prey). This process is called biomagnification and is characterized by biomagnification or trophic magnification factors (BMFs or TMFs, respectively). AHSs can be roughly divided into known chemicals of concern, such as persistent organic pollutants (POPs), and contaminants of emerging concern (CECs), that include novel flame retardants, polymer additives, and many more. Both the production and use of a number of AHSs have been regulated since the 1970s. To understand the outcome of the regulations, retrospective analysis of samples from different years, a time-trend study, is often utilized.

The main aim of this work was to develop a non-selective sample extraction, purification, and analysis method, and then find and identify as many biomagnifying contaminants as possible. To assess both biomagnification and temporal trends of a wide range of chemical contaminants in a given Baltic Sea food web, non-target screening (NTS) was used. A clean-up method was established and tested with a satisfactory outcome: processed extracts were pure enough for gas chromatography-mass spectrometry (GC-MS) analysis. Also, accompanying NTS data processing workflows were developed. Application of these resulted in BMFs for more than 100 contaminants (Paper I). The data processing workflow was refined for faster detection of chemicals that demonstrate temporal trends and/or biomagnify. It was possible to detect and tentatively identify more than 300 legacy POPs and CECs with statistically significant temporal trends in three Baltic top consumers (Paper II). Adjusted NTS workflows were used to reveal more than 250 compounds that possessed trophic magnification properties (Paper III). Inspired by the discovery of a novel flame retardant Dechlorane 602 (Paper I), a suspect screening for dechlorane-related compounds and their transformation products was carried out. A total of 31 compounds were detected and tentatively identified, many of which showed significant temporal trends and biomagnification (Paper IV). A number of compounds reported in Papers I–IV were tentatively identified for the first time in wildlife. In addition, the papers provide valuable spectral and retention information for the researchers in the field.

In conclusion, this thesis presents useful GC-MS-based NTS workflows and biomagnification or time-trend data for a plethora of organic contaminants in the Baltic Sea food web. The data can contribute to i) the assessment of the influence pollutants have on the ecosystem and ii) various mitigation actions for AHSs, such as evaluating dechloranes for regulation under the Stockholm Convention on POPs, helping in the fight for a better environment and future.