PCB and PAH dynamics in a small rural lake

Sediment traps were deployed for periods of 4-5 weeks between May 1990 and September 1991 at depths of 6.5 and 12.5 m in a 15 m deep, rural U.K. lake. Trap material was quantitatively analyzed for 14 PAH compounds, 43 PCB congeners, particle mass, and C and N contents. Derived depositional fluxes of total PAHs (11.7 mg m(-2) yr(-1)) and total PCBs (289 and 463 mu g m(-2) yr(-1) at 6.5 and 12.5 m, respectively) are at the upper ends of the ranges reported in other comparable studies. The annual fluxes of individual PAH compounds are generally similar to accumulation rates determined for surface sediments at the same location, indicating the absence of significant recycling. The ratios of annual depositional fluxes to surface sediment accumulation rates are substantially greater than 1 in the case of phenanthrene (2.5) and PCBs (6.5-23). These relatively elevated fluxes combined with a consideration of particle dynamics in the lake suggest significant recycling between the sediments and water column, involving remobilization into solution accompanied by diffusive release. Recycling of PCBs tends to increase with increasing aqueous solubility. The depositional fluxes of PAHs and particle mass showed a similar seasonal dependence with the highest fluxes occurring in winter, when the water column was well-mixed. The high winter fluxes appear to be due to combination of high catchment-derived inputs (PAHs and particle mass) and atmospheric inputs (PAHs) and to sediment resuspension.