Spatial distribution of PCDDs, PCDFs and dl-PCBs along the cascade of urban reservoirs

The river environment is a highly complex system with a variety of processes continuously changing along its continuum (River Continuum Concept). Therefore identification of the threats that result from different elements of the river ecosystem is an intricate task, mainly because of the transportation and biological, geological and chemical processes occurring in such a system. The overall objective of the presented study was to examine the concentration and pattern of polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in the five urban, cascade reservoirs. The obtained data demonstrated an increasing total concentration of toxic PCDDs/PCDFs and dl-PCBs along the studied reservoirs starting from 266 ng/kg d.w. in the first pond up to 11,400 ng/kg d.w. in the last pond, wherein the highest World Health Organization - Toxic Equivalent (WHO-TEQ) concentration (18.9 ng TEQ/kg d.w.) was also recorded. The exception from this rule, with the lowest total and WHO-TEQ concentrations (182 ng/kg d.w. and 1.31 ng TEQ/kg d.w., respectively) was the middle newly constructed III reservoir, equipped with the sediment traps and sand separators at the stormwater outlets and ecotone zones around its catchment for enhancing the purification of inflowing stormwater. This situation may indicate the importance of such solutions for the reduction of PCDDs, PCDFs and dl-PCBs in the urban water ecosystems.