Transport of polychlorinated biphenyls in urban cascade reservoirs: levels, sources and correlation to environmental conditions

Intensified human impact in urban catchments is reflected through degradation of hydrological cycles and acceleration of matter, energy and pollutants flows. In this study the comparative analysis of occurrence, concentrations and transfer of twelve dioxin-like PCBs in the bottom sediment collected from five cascade reservoirs located on the Sokołowka River (in the northwestern part of the city of Łodź, central Poland) were determined using isotopically labelled internal standards and HRGC/HRMS. The total concentration of analyzed PCBs ranged from 79.75 to 3,741.34 ng/kg d.w. with maximum concentrations in the last two reservoirs (3,741.34 and 2,594.36 ng/kg d.w., respectively). Reservoirs situated at the beginning of the cascade system showed concentrations several times lower: 694.32 in the first, 292.15 in the second and 79.75 ng/kg d.w. In the third reservoir. The obtained data showed moderate or strong correlations between PCB concentration in sediments and environmental conditions of the water column: pH (-0.81), conductivity (0.94), mineral suspended solids (0.82), total and organic suspended solids (0.61), total phosphorus (-0.83) and total nitrogen (0.67). Furthermore, these parameters could have played an indirect role in PCB reduction through the stimulation of phytoplankton production. This in consequence might have influenced PCB pathways in reservoirs through changes in their sedimentation, transport and degradation processes as significant relations between PCBs and chlorophyll a content was found (0.64).