Multimedia Models and Observations in Concert - A Powerful Tool to Understand and Manage Organic Contaminants

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A key goal of environmental authorities is to minimize the exposure and effects on the environment and humans from harmful organic contaminants. Sound chemical control strategies therefore require the determination of the quantitative relationship between emissions, environmental levels, and human exposure to chemicals of concern (or so-called source-receptor relationships). To achieve this, substantial information is required on which chemicals that are present in the environment and on their concentrations and behaviour in the environment and the food-chains. Large resources are already invested into monitoring trace levels of POPs and screening for chemicals of emerging concern in air, sediments, fish, birds, or other environmental compartments through various monitoring and screening programmes. This report has explored the potential added value of combining empirical results from monitoring and screening studies with the use of multimedia environmental models.

Environmental measurements and modelling approaches each have their strengths and limitations that can complement each other. Model simulations can help to optimize sampling design for measurement campaigns by for example predicting the key physical matrices or biota where the compounds of interest are expected to be found at elevated levels, the anticipated concentrations and hence necessary detection limits, the optimal sampling region or even time of sampling for the specific objectives of the study. Hence, use of limited resources in future monitoring and screening studies can be optimized and invested where they are predicted to maximize the value of the results. This was illustrated by the study of cVMSs in the Arctic atmosphere, where predictions of the atmospheric behavior of D5 was a key to design both the hypotheses, the method development, and the location and timing of the field campaigns.

Models can also serve as tools to rationalize existing observed measurements and hence provide mechanistic explanations for the observations that can be hard to derive from the measurements alone. This was clearly exemplified by the study of cVMSs in the Inner Oslofjord, which was spurred by the detection of elevated levels of cVMSs in fish from this fjord. The models served to rationalize these measurements and to provide important insights into key processes of the environmental and food-chain behavior of cVMSs in this environmental system. Also, the detection of D5 and D6 in air at the Zeppelin observatory is a much stronger evidence for long-range atmospheric transport of these compounds when they in addition can be backed up by mechanistic models that explain the observations.

Models gather the existing understanding about relevant systems and processes in one place. This means that comparisons of model predictions and observations can contribute to evaluate our current understanding, and to identify key knowledge gaps where models and measurements do not agree. This was seen in both the study of cVMSs in the Arctic atmosphere and the Inner Oslofjord, as well as in the study of SCCPs in the Nordic environment where this was one of the key objectives. The latter study also confirmed that our overall understanding of the link between environmental emissions and human body burdens of SCCPs in the Nordic environment is fair, but also highlighted aspects which require further research for this complex group of chemicals. Moreover, to facilitate these model-measurement comparisons, strategic sampling is encouraged to provide observations that are comparable to results from the model simulations.

Only by combining measurements and models can uncertainties be identified and reduced and confidence in source-receptor relationships increased. The case-studies in this project illustrate the immense value of integrating multimedia models and observations in concert as a tool for improved understanding and management of organic contaminants in the Nordic environment. We hope that these modelling tools could be of relevance to future Norwegian and Nordic screening and monitoring efforts, as well as to relevant policy activities in the Nordic region related to organic contaminants.

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