long-term fate and bioaccumulation of PCBs in Puget Sound,
Models of contaminant kinetics:
- Davis 2004 includes an active 10cm layer in Puget Sound
- Field data: In Puget Sound 1400kg PCBs (estimates range from 600-3500) are in active layer compared with ~7kg in water and ~40kg in biota (estimated from Sandy’s measurments)
- [PCB] in water: measured mean ~60-100 ng/gD.
- Model says PCB mass in sediment will plateau in ~50yrs at 1000-8000kg and depend mostly on on-going external loading ( from 25 to 500 kg/yr) not historical because it is getting buried by new sedimentation)
- Atmospheric deposition is l~50kg/yr and ocean exchange may be 100s kg/yr… these numbers are uncertain but may mean PCB mass is actually increasing in Puget Sound now.
- Long-term means of 20-200kg/year is about what must have been loaded to get to current measured masses.
Since 1990s, English sole PCBs have been increasing (but not in other species). This may be caused by on-going external loading. Our model predictions match measured biota within a factor of 2.
External loading in Puget Sound is probably non-point source from watersheds. Policies that control general toxics loading and runoff should help reduce PCB loading.
Scott: External loading is still a problem?! The orca community should be lobbying HARD for global PCB bans!