This report presents a summary of the results within the Swedish National Monitoring Programme for Contaminants in marine biota with focus on the last 10 years (latest data is from 2023).

For the biological parameters, there are no systematic temporal changes for age, length or weight of fish during the last ten years. However, for herring, we find a systematic decrease in the fat percentage across most stations. It is most pronounced in the Bothnian Bay with yearly changes above 10% for many stations. Stable isotopes (N and C) were included in the program in 2013 and we are starting to get a better understanding of the baseline for the individual species and changes over time. No trends currently stand out.

For metals there are few significant trends for the last 10 years. There is a general increase in Cd and Cu, a decrease in Pb and no general direction of trends for Hg. Concentrations of Cd and Pb are below threshold and concentrations of Hg are around threshold.

Chlorinated pesticides are decreasing across all compounds, station and species and DDE, sum-HCH and HCB are at or below threshold.

Polychlorinated biphenyls (PCB) show spatial differences between the subgroups non-dioxin-like PCBs, non-ortho dioxin-like PCBs and mono-ortho dioxin-like PCBs, and with increasing numbers of chlorines. For herring, there is a general decrease, although the non-ortho dioxin-like PCBs and the mono-ortho dioxin-like PCBs show some increases in the northern Baltic Sea and the Kattegat especially for the highly chlorinated congeners. Concentrations of PCB-118 and PCB-153 are at or below threshold.

Polychlorinated dibenzodioxins/-furans (PCDD/F) decrease for the less chlorinated congeners in the Baltic Proper. We suggest that the apparent increase for congeners with higher chlorine numbers is caused by a few outliers and therefore should not currently be a concern. The TEQ values for PCDD/Fs are below threshold.

Brominated flame retardants (BFR) are steady or decreasing with the exception of mussels. For mussels an abrupt increase in concentrations is seen after a change in analysis laboratory and we suggest differences in analytical methodology is causing this recent increase. Sum PBDE and HBCDD are above and below threshold for all fish, respectively.

Perfluoroalkyl substances (PFAS) show many significant trends for herring but less so for other biota. For herring trends separate into substances that show decreasing trends (PFOA, PFDoDA, PFTrDA, b-PFOS, l-FOSA, b-FOSA), those that show increasing trends (PFDA, PFUnDA, l-PFOS) and mixed trends (PFNA and PFTeDA). The increases are concerning as these deviate from recent studies suggesting that these PFAS substances were beginning to decrease in the Baltic Sea. This development should therefore be followed closely. PFOS is below threshold for all fish.