Environmental fate of PCDD/Fs: Atmospheric concentrations, seasonal trends, exchanges in different environments, risk...

This study evaluated atmospheric gas- and particle-phase levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), including 17 individual congeners and the sum of tetra to octachloro homologues. The investigation was conducted across urban, semi-rural, and wastewater-treatment-plant-impacted areas in Bursa, Türkiye. The annual mean concentration of Σ₁₇PCDD/F in the gas phase was determined to be 82.27 ± 11.97 fg/m³, whereas the corresponding value for the particle phase was 327.53 ± 130.44 fg/m³, resulting in a total concentration of 409.80 ± 133.09 fg/m³. The corresponding toxic equivalent (TEQ) level was 30.30 ± 5.11 fg TEQ/m³ (range: 22.58-39.21 fg TEQ/m³). Approximately 78 % of the Σ₁₇PCDD/F concentrations were associated with the particulate phase, and this proportion increased further during winter due to elevated emissions and reduced atmospheric dispersion. Using the measured atmospheric data, theoretically estimated equilibrium concentrations were calculated for soil, leaves, tree bark, and water media. It was observed that highly chlorinated congeners predominated in these environments, with an increased tendency for accumulation, particularly during colder periods. Predictions of particulate-phase concentrations using a K_OA-based equilibrium model were consistent with measured data for 2,3,7,8-TCDF; 2,3,7,8-TCDD; and 1,2,3,4,6,7,8-HpCDD; however, notable deviations were observed for highly chlorinated congeners. Principal Component Analysis (PCA) revealed four distinct source groups explaining 79.02 % of the total variance, highlighting waste incineration, vehicular emissions, industrial production, and biomass combustion as the predominant contributors. Inhalation-based risk assessments showed that daily intake doses were below the WHO-recommended thresholds, and the estimated cancer risks remained lower than the 10^-6 benchmark level.