WP20 Contaminated Harbor and River Sediment
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(SCH-1117-836840) PCB Partitioning to Flocculated Hudson River Sediment: Recharge of the Labile Pool.

Schneider, A¹, Porter, E¹, Baker, J¹, ¹ University of Maryland Chesapeake Biological Laboratory, Solomons, MD, USA

ABSTRACT- Numerous studies demonstrate that PCB desorption from sediment and soil is a two-stage process; the first ('labile') is rapid and reversible and the second ('resistant) is slow and irreversible. After a resuspension event it is unclear whether the labile pool is replenished from the resistant pool as sediments sit unmixed on the river bottom. In this study, both the desorption rates of individual PCB congeners from Hudson River sediment as well as their apparent partitioning coefficient were measured by repeatedly resuspending field-collected sediments into clean water in large mesocosms. Dissolved PCBs were measured using solid phase microextraction (SPME) to minimize the impact of colloids. Steady state PCB partitioning was reached by the start of the second day of each resuspension event and occurred on the same time scale as floc formation. When the sediment was initially resuspended there was a large release of PCBs into the dissolved phase. After just two hours of resuspension 25% of the total PCBs in the water column were in the dissolved phase. When the same sediment was resuspended for a third time only 15% of PCBs were in the dissolved phase. In the mesocosm with only one day of quiescence between resuspension events, the partition coefficient of the lower molecular weight congeners increased 35 to 65% from the first to the third resuspension event. When the quiescent time was increased to four days, the partition coefficient increased by only 15 to 20%. It appears that chronic resuspension resulted in less PCB release per event due to the slow recharge of the labile pool. For the low molecular weight congeners the labile pool recharged after approximately four days of quiescence. For the higher molecular weight congers the recharge rate is slower and four days of quiescence was insufficient to replenish the labile pool.

Key words: desorption, Hudson River, PCBs, partitioning