Fate of polycyclic aromatic hydrocarbon (PAHs) in urban lakes under hydrological connectivity: A multi-media mass balance approach

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic pollutants widely present in various environmental media. Some PAHs have carcinogenic, teratogenic, and mutagenic effects. Urban lakes are severely polluted by PAHs due to human activities. Longyang Lake (LL) and Moshui Lake (ML), which serve as entry lakes for Wuhan's “Six Lakes Connectivity” project, were chosen as the study areas to learn about the migration of PAHs. Water flows from LL to ML through the Mingzhu River. Multi-Media Mass Balance Model (MMBM) and fugacity fractions (ff) were used to characterize the migration of PAHs under the hydrological connectivity project. Compared to ff, the MMBM can describe the migration of PAHs in a more detailed and quantitative way. The concentration of PAHs in water of LL decreased from 36.5 ng L−1 to 26.59 ng L−1 over 43 days, while those in ML increased from 46.8 ng L−1 to 198.25 ng L−1 over 141 days. Sediment takes a longer time to decrease to stabilization. The concentration of PAHs in the sediment of LL decreased from 932 ng g−1 to 0.95 ng g−1 over 13.33 years, while those in ML decreased from 4812 ng g−1 to 1.04 ng g−1 over 16.96 years. The stabilized concentrations were consistently lower than the observed concentrations and fell below the modeled stabilized concentrations obtained in the unconnected case (2170 ng L−1 in water and 40.81 ng g−1 in sediment). The MMBM showed that PAHs in the lake are mainly exported through runoff. However, modeling results indicated that upstream LL did not increase total PAHs concentrations in the ML because the output from ML was significantly higher. Sediment parameters sensitively influenced the results of the model. Although the simulation results showed reductions of PAHs pollution in two lakes under the hydrological connectivity project, long-term monitoring results are needed to optimize the model. [Display omitted] •The Multi-Media Mass Balance Model details migration trends of PAHs.•Concentrations of downstream PAHs were not enhanced by inputs of upstream lake PAHs.•Hydrological Connectivity Project reduced PAHs concentration in both lakes.