Polychlorinated biphenyls (PCB) in a river ecosystem

Atmospheric deposition is one source of persistent pollutants such as polychlorinated biphenyls (PCB) in aquatic environments. Other point sources can also contribute to the PCB loadings in the water. In the Emån River, in southeast Sweden, contaminated sediment was a source of PCB, the largest deposits of it being found in a small lake connected with the river, Lake Järnsjön, the sediment of it contained about 400 kg of PCB. The concentration of PCB in the water and in the fish was more elevated downstream from the lake than at upstream sites. Lake Järnsjön was cleaned up by the dredging of it during 1993 and 1994. The dredged sediment, estimated to contain over 95% of the PCB in the lake, was deposited in a landfill. During the cleanup action, the concentration of PCB downstream from the lake did not become higher than before. The PCB concentration in the air around the landfill increased in the vicinity and during construction of the landfill. After closure of the landfill by a layer placed on top of it, the PCB concentration in the air fell to background levels. No increase in the PCB concentration in the ground water around the landfill as a result of the remedial action could be detected. Monitoring carried on for two-years following completion of the remediation showed there to be a decrease in the PCB concentration in the water of the lake. The PCB was found to vary seasonally with water discharge and with temperature. The PCB concentration was highest at low water discharge and high temperature. Both the levels of PCB and the variations in them approached those found at the upstream location. There, precipitation was found to be the main source of PCB during high water discharge, desorption from the sediment prevailing under conditions of low water discharge. In the summer of 1996, nearly two years after remediation had been completed, an investigation of the PCB concentration in the fish of the river system was conducted. This investigation was a repetition of one made in 1991, prior to remediation. It showed that after remediation the concentration of PCB in one-year old fish in Lake Järnsjön was halved. The concentration of PCB in fish upstream was also lower, probably because of the decrease in overall background contamination