Spatio-Temporal Patterns of Polycyclic Aromatic Hydrocarbons and Phthalates Deposition in Sediments of Reservoirs: Impact of Some Environmental Factors

The aim of this study is to assess the accumulation rates of polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PAEs) in the Nielisz Reservoir. Sediment traps were used at three sites: the upper (N1 station), central (N2 station), and near-dam (N3 station) zones, where they were installed at the bottom in the littoral zone of the reservoir at depths ranging from approximately 1.6 m to 2.5 m. Sampling took place from June to August 2019, and entrapped sediments were analyzed for 16 PAHs and 11 PAEs. Four PAHs, naphthalene (NAP), phenanthrene (PHE), benzo(b)fluoranthene (B(b)F), and benzo(a)pyrene (B(a)P), and two PAEs—di-n-butyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP)—were identified. Among PAHs, 5-ring compounds dominated, while DBP was the most common PAE. PAH and PAE concentrations in entrapped sediments showed both temporal and spatial variability, but no clear trends were established. The accumulation rate of Σ4PAH ranged from 47.8 to 458 μg/m2d, with a decreasing trend from the inflow to the dam. The light-to-heavy PAH ratio suggests a pyrogenic origin. Σ2PAE fluxes were lower, between 1.81 and 17.6 μg/m2d, with no clear spatial variation along the reservoir. Ecotoxicological analysis indicated that PAHs and PAEs could occasionally harm benthic organisms, mainly due to B(b)F. The deposition rates of both PAHs and PAEs are strongly linked to the accumulation of suspended particulate matter (SPM) and organic carbon, particularly of autochthonous origin. Additionally, the pH and salinity of the water significantly influence the accumulation rate of the studied contaminants, especially PAHs.