Model Approach

Biomagnification of POPs in the present study was calculated using the OMEGA bioaccumulation model,³¹ combining mass balance and allometric approaches to estimate bioaccumulation in each tropic level individually and biomagnification throughout the food chain.²⁴ Since its development, OMEGA has effectively been applied in estimating biomagnification of numerous organic compounds and metals.²³⁻²⁵ We assumed a steady-state concentration of chemical residues in aquatic organisms (C_i,x, in μg/kg lipid weight (l.w.)), calculated as the sum of influx via water (absorption) and uptake from food (assimilation) divided by the total elimination rate, encompassing elimination via water, biotransformation, excretion, and dilution through growth, disregarding possible uptake and elimination through air. The steady-state concentration in an organism is calculated as³¹

where C_i,x is defined as the final steady-state concentration of substance x at trophic level i (in μg/kg lipid weight), k_0,x,in is the chemical absorption rate (in L/kg·d^–1), C_0,w,x is the initial chemical concentration in the water (in μg/L), k_1,x,in is the chemical concentration assimilation rate in [kg/kg·d^–1], C_i–1,x is the chemical concentration in food (in μg/kg), and ∑k_j,x,out is the sum of the elimination rate constants (per day), pertaining to water (including urine), feces, growth dilution, and biotransformation. Concentration estimates in the model were based on wet weights and were transformed into lipid weight-based estimates using reported data on the whole-body lipid content. As the Arctic is a highly dynamic system, with algae blooms in spring and changes in the lipid content of zooplankton and species at higher trophic levels throughout the year, the assumption of a steady-state concentration may not be justified in a highly dynamic system such as the Arctic, especially for lower trophic levels.²⁵ Furthermore, the OMEGA model only includes the main aquatic exposure routes and does not take into account any possible exposure of POPs through air (Text S1 in the Supporting Information (SI)).