Sources of polychlorinated dibenzo-p-dioxins and dibenzofurans to Baltic Sea herring

Levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in herring (Clupea harengus) remain high in several parts of the Baltic Sea, despite declines in PCDD/F emissions since the 1980s. The reasons behind this are not well understood. This study applied a statistical modeling approach where sources of PCDD/Fs that contaminate Baltic biota were quantitatively assessed by analyzing existing datasets. PCDD/F patterns were extracted from a herring dataset using positive matrix factorization (PMF). The extracted biota patterns were transformed into sediment patterns using fish-to-sediment transformation factors, and the resulting patterns were compared with known source PCDD/F patterns. The model distinguished three model patterns, which explained 85% of the data. These patterns were matched to tetra-chlorophenol (TCP), penta-chlorophenol/atmospheric background (PCP/AB), and thermal source patterns, respectively. The thermal source was the largest contributor to toxic equivalents (TEQ) in herring, but the level decreased from 42 ± 9.0 pg TEQ g^-1 lipid weight (lw) before year 2000 (pre-2000) to 15 ± 2.4 pg TEQ g^-1 lw post-2000, i.e., a decline of around one-third in the original TEQ concentration. The contribution of TCP more than doubled, from 2.1 ± 0.62 pg TEQ g^-1 lw to 5.6 ± 1.1 pg TEQ g^-1 lw, and the relative contribution of PCP/AB also increased. These increasing trends suggest that, as primary air emissions of PCDD/Fs are managed and levels decline, the impact of TCP and PCP/AB sources on Baltic Sea biota will become more important over time and that PCDD/F-contaminated sites in coastal areas and marine environments require more attention.