Fat content and condition factor explain levels of dioxins and PCBs in whitefish (Coregonus sp.) from Sweden’s major lakes

Whitefish ( Coregonus sp.) are an ecologically and economically important species in large, temperate lake ecosystems, including North America’s Laurentian Great Lakes. While levels of persistent organic pollutants have generally declined in many large-lake systems, unexpectedly high concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDDFs), and biphenyls (PCBs) have been detected in whitefish from Sweden’s two largest lakes, Vänern and Vättern, prompting an extensive investigation. This study analyzed 282 whitefish samples collected between 2015 and 2022 from these lakes and from the Gulf of Bothnia—a large, brackish basin of the Baltic Sea known for long-standing contamination issues. Whitefish dorsal muscle tissue was collected from commercial catches and analyzed to quantify the contaminant levels. We used generalized linear models to assess which spatial, temporal, and morphometric variables explained variation in toxic equivalent (TEQ) levels. While whitefish from Lake Vänern had higher contaminant levels than those from oligotrophic Lake Vättern, this difference was largely explained by their higher fat content. The total length was positively associated with TEQ, while the condition factor showed a negative association in Lake Vättern whitefish, suggesting a greater mobilization of contaminants from lipids to muscle due to starvation-related effects. Similar to recent observations in some Laurentian Great Lakes, we found no significant temporal decline in TEQ during the study period. Our findings provide a European large-lake perspective on the complex factors governing contaminant bioaccumulation in a key fish species, offering valuable comparative insights for Great Lakes science and management.