Effects of microplastics on polycyclic aromatic hydrocarbons migration in Baiyangdian Lake, northern China: Concentrations, sorption–desorption behavior, and multi-phase exchange

Microplastics (MPs) and polycyclic aromatic hydrocarbons (PAHs) have been found in all environment matrices and are of concern worldwide. In this study, PAHs were determined in Baiyangdian Lake, China, and the effects of MPs on the migration of PAHs at the lake interfaces were analyzed. The average abundances of detected MPs were 9595 items m for water and 1023 items kg for sediment. The detected MPs were polyamide 6, polypropylene, polyethylene, and polyethylene terephthalate. The average ΣPAHs in the water, sediment, and air were 1338 ng L, 751 ng g dry weight, and 395 ng m, respectively. At the air-water interface, naphthalene, and phenanthrene volatilized from water to air, whereas benzo(b)fluoranthene, benzo(k)fluoranthene, and dibenzo(a,h)anthracene deposited from air to water. The fugacity fraction between sediment and bottom water ranged from 0.88 to 0.99, which indicated net volatilization at the water-sediment interface. The adsorption capacities of the four MPs for the PAHs ranged from 39.4 to 99.8 μg g with a desorption efficiency range of 0.01%-44.3% under oscillation. According to the distribution of PAHs on the MPs, the exchange fluxes of PAHs at the water-air and sediment-water interfaces were recalculated. The results showed that the MPs could increase deposition of the PAHs from air to the water (ΔF: -221 × 10 to -0.01 × 10 ng m d) and the volatilization of PAHs from sediment to water (ΔF: -79.7 × 10 to 180 × 10 ng m d), which suggests that MPs increase the risk of PAHs in water and to aquatic organisms.