Baltic Sea sediment records: Unlikely near-future declines in PCBs and HCB

- Temporal trends of PCB levels in coastal sediment followed global emissions of PCB.
- Response in offshore PCB levels to decreased emissions was delayed with 10-15 years.
- HCB concentrations increase in offshore sediment after 2000.
- The reduction in PCB from peak level has levelled off during the last two decades.
- No major differences in spatiotemporal trends of PCDD/Fs and PCBs

We present a comprehensive study on PCBs and HCB in dated sediment cores from the Baltic Sea covering the 20th century, and compare their spatiotemporal trends with those of PCDD/Fs from the same areas. PCB concentrations in coastal impacted sediment followed the temporal trend of estimated global emissions of PCBs and thus responded quickly to changes in global industrial use, whereas concentrations in offshore sediment needed 10-20 years longer to respond. Differences in spatiotemporal trends of PCDD/Fs and PCBs were smaller than expected based on documented differences in key sources and source areas. Sediment concentrations of HCB varied little over time and space, but concentrations are increasing in recent years. The steep PCB concentration reduction over time observed for the late 20th century levelled off during the last 20 years, and levels of PCBs appear to be at or near a steady-state condition.CapsulePCB concentrations in Baltic Sea sediments appear to be at or near steady-state, and no significant concentration decreases are to be expected in the near future.