Abstract
The levels of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in the Pilica River and Sulejów Reservoir were found to be 46% higher during the flood season than during stable flow periods. In addition, PCDD/PCDF and dl-PCB mass loads increased by 5- to 12-fold and by 23- to 60-fold for toxic equivalency (TEQ) during flooding. The Sulejów Reservoir was found to play a positive role in reducing PCDD, PCDF and dl-PCB transport within the study period, with reductions ranging from 17 to 83% for total concentrations, and 33 to 79% for TEQ. Wastewater Treatment Plants (WTPs) were not efficient at mass concentration removal, with small displaying the least efficiency. WTPs discharge pollutants into the aquatic environment, they also produce sludge that requires disposal, similar to reservoir sediments. Sludge- or sediment-born PCDDs, PCDFs and dl-PCBs may be removed using phytoremediation. The cultivation of cucumber and zucchini, two efficient phytoremediators of organic pollutants, on polluted substrate resulted in a mean decrease in PCDD + PCDF + dl-PCB TEQ concentrations: 64% for cucumber and 69% for zucchini in sludge-amended soil, and by 52% for cucumber and 51% for zucchini in sediment-amended soil.
Highlights
A river catchment is a highly-complex ecological system
PCDD, polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) concentrations are known to increase along a polluted river, reaching a peak in the mouth section[6,8,9,10,11,12,13]
We observed strong reductions of total PCDD + PCDF + dl-PCB concentration (33%) and toxic equivalency (TEQ) concentration (38%) during stable flow in the river section between the Koniecpol and Sulejów sampling stations (100.4 km length of river section): a sector covered by natural vegetation, dominated by riparian willow communities. These results indicate that the presence of natural floodplain terraces in river valleys significantly increases the rate of self-purification of the river[42,43], and can reduce the transport of PCDDs/PCDFs and dl-PCBs along the river continuum
Summary
A river catchment is a highly-complex ecological system. Hydrological pulses facilitate the transport of nutrients, mineral and organic matter along the river continuum[1]. The levels of anthropogenic pollutants in the river basin, including toxic organic compounds and endocrine disruptors are increased by human activity As they are positioned at the lowest points in the landscape, rivers often accumulate pollutants transported via atmospheric deposition, runoff from urban and agricultural areas or inflow through point sources[2,3,4,5]. Low water solubility of PCDDs, PCDFs and dl-PCBs allows them to bind to the organic and mineral particles in the river; in this bound form, they are transported along the river continuum and deposited downstream. After deposition, they gradually accumulate in sediments, which serve as long-term sources of pollutants. The findings are used to improve the quality of the environment (developing methods and tools for reduction of identified threats)
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