Phthalate Fate in the Hydrographic Network of the River Seine Basin (France) Under Contrasted Hydrological Conditions

Our main objective was to characterize phthalate transfer mechanisms in the river Seine basin (France) under contrasted hydrological conditions. Phthalates were present in rural as well as in urban areas, and di-(2-ethylhexyl) phthalate (DEHP) was always prevailing. Hotspots of DEHP water concentrations were identified along the river Seine at wastewater treatment plant (WWTP) and combined sewer overflow discharge locations. A spatial concentration increase was found (×2 for di-ethyl phthalate and di-n-butyl phthalate and ×3.5 for DEHP) from upstream to downstream of the urbanized areas. Comparing hydrological conditions in the river Seine, from low to high water, a six-time increase in concentrations was found downstream of the urbanized areas, while a dilution process occurred at the rural station due to slightly contaminated inputs. A strong enhancement of annual specific flux for DEHP was estimated from upstream (33 g km−2 year−1) to downstream (114 g km−2 year−1) of the urbanized areas, corresponding to annual inputs of 4.9 t. The monitoring of a combined sewer overflow discharge, following a strong storm event, showed a preferential distribution of compounds in the surface microlayer. DEHP enrichment ratios between subsurface and surface microlayer were for the dissolved and the particulate phases 2.7 and 15, respectively. Even at the very upstream part of a rural elementary basin, impact of runoff input prevailed against that from WWTP discharge. Moreover, in a suburban basin equipped with a separate sewer system, increase in phthalate concentrations under high flow conditions was strictly related to runoff processes. Comparison of inputs between separate (Orge) and combined (Seine) systems indicated a 9.7-times higher pollutant inputs as square kilometer of surface basin from the combined one.