Spatial distribution of organic pollutants (PAHs and polar pesticides) in the floodplain of the Ohře (Eger) River, Czech Republic

Abstract

The spatial distributions of organic pollutants, polycyclic aromatic hydrocarbons (PAHs), and polar pesticides were studied in the floodplain of a Middle European lowland river (the Ohře River, Czech Republic) to evaluate their possible use for pollution chemostratigraphy. The floodplain evolution and internal structure were evaluated from historical maps, a digital terrain model, and electric resistivity tomography (ERT) at sampling sites. The approximate age of the sediments was inferred from pollution by Cu, Pb, and Sn (sixteenth century and younger), as well as Hg and U (nineteenth to twentieth centuries), based on the known history of metal mining in the Ohře catchment. Polycyclic aromatic hydrocarbons, as non-polar persistent pollutants, have a stable stratigraphic distribution, with peak concentrations attributed to the local peak in the use of coal under low environmental concern from the middle nineteenth century to the late twentieth century as well as a minor peak due to more ancient charcoal production. Polar pesticides range from partially migrating (e.g. atrazine, simazine, and chloridazon) to very mobile ones with depth profiles that are not related to the sediment stratigraphy (e.g., chloroxuron and acetochlor). The post-depositional pollution maxima of the latter are near the contacts of more permeable channel sands and overlay finer, less permeable deposits near the accumulation of mobile elements (Ca, Mn) and minor secondary maxima for Hg and U pollutants. Polycyclic aromatic hydrocarbons can be used for pollution chemostratigraphy; the use of more mobile polar pesticides is limited. The occurrence of pesticides in the forested channel belt (not used for agriculture) and their seasonal variation document considerable dynamics of polar pollutants in fluvial systems.