Distribution, sorption patterns, and outflows of riverine microplastics-affiliated linear alkylbenzenes and polycyclic aromatic hydrocarbons in a dynamic coastal zone

Microplastics (MPs) pollution has emerged as a global concern. To mitigate the potential threats by MPs, particularly to coastal regions, it is crucial to comprehend the environmental behavior of MPs and their affiliated chemicals. In the present study, we collected floating MPs using a Manta net (0.33 mm mesh size) in a one-year sampling event in 2022 from the eight major estuaries in the Pearl River Delta, China, and also from five coastal sites in August and December in the same year. Nineteen linear alkylbenzenes (∑₁₉LAB) and 16 polycyclic aromatic hydrocarbons (∑₁₆PAH) affiliated with MPs were measured. The mean concentrations of MPs-affiliated ∑₁₉LAB and ∑₁₆PAH were 6710 (range: 3400–12300) and 5310 (range: 817–19,600) ng g^–1, respectively, at the estuarine sites, and were 4920 (range: 2400–7600) and 2610 (range: 911–7890) ng g^–1, respectively, at the coastal sites. Significant correlations were found between logarithmic MPs–water partition coefficients (log K_pw) and logarithmic suspended particulate matter–water partition coefficients (log K_d) values for LABs and PAHs, indicating analogous partitioning dynamics for MPs and suspended particulate matter with water. The annual riverine outflows were 1170 and 414 g for ∑₁₉LAB and ∑₁₆PAH, respectively. Although the riverine outflows of LABs and PAHs carried by MPs remain negligible compared to those by suspended particulate matter, an upward trend was identified between 2018 and 2022. Notably, the riverine input of LABs and PAHs carried by suspended particulate matter to the coastal ocean decreased from 2005/2006 to 2022, due to a combination of improved technological processes and energy structures.