Ecological regime shifts enhanced the contribution of microplastics to the burial of polycyclic aromatic hydrocarbons by sediments.

Ecological regime shifts and contamination of polycyclic aromatic hydrocarbons (PAHs), and microplastics (MPs) were found in many waters. How ecological regime shifts influence the contribution of microplastics to the burial of PAHs in sediments is unclear. Sediment cores in the largest lagoon (Lagoon Pinqing) of China were used to address this issue. Regime shifted from phytoplankton dominance to macrophyte dominance in the late 1970s in Lagoon Pinqing. The factor affecting the contribution of microplastics to the burial of PAHs in sediments varied from total phosphorus to total nitrogen during the periods from 1965 to 1970s, and from 1970s to 1990s. Phytoplankton dominated from the late 1990s to 2017. The increased aromaticity of sediment organic matter induced by regime shifts enhanced this contribution in this period. This contribution varied from 0 to 67.2%, influenced by the regime shifts in different periods. This contribution for the PAHs with moderate hydrophobicity was more susceptible to regime shifts than other PAHs. Our results suggested the contribution of microplastics to the burial of PAHs by sediments could be influenced by ecological regime shifts, and driven by various factors.