Occurrence, distribution, and ecological risks of organic pollutants in global mangrove sediments

Mangroves are one of the most important intertidal ecosystems in the tropics and sub-tropics, with high productivity and biodiversity. However, mangroves are increasingly threatened by anthropogenic organic pollutants. While numerous studies have reported the presence of organic pollutants in mangrove sediments, a comprehensive global synthesis focusing on the occurrence, distribution, and sources of organic pollutants in mangrove ecosystems remains lacking. To bridge these gaps, a systematic review was conducted based on data from 724 sediment samples in 25 mangrove ecosystems worldwide, covering 212 organic pollutants. The results showed that polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), flame retardants (FRs), chlorinated pesticides (CLPs), perfluoroalkyl polyfluoroalkyl substances (PFASs), and chlorinated paraffins (CPs) were the main compounds detected in mangrove sediments, with median concentrations of 9.37-2435 ng/g, 0.39-165 ng/g, 0.04-27 ng/g, 0.12-31.32 ng/g, 0.33-10.19 ng/g and 269-404 ng/g, respectively. Among all compounds, PAHs and PCBs were the predominant researches focus, while efforts toward detecting emerging pollutants (CPs and PFASs) have increased in recent years. Pollution research showed significant geographical imbalances, with studies in major mangrove-rich regions such as Indonesia, Brazil, Nigeria, and Mexico remaining critically underrepresented in the literature. Key environmental factors, such as the total organic carbon content and sediment grain size, influence pollutant behavior in mangrove sediments. Further source analysis showed that organic pollutants originated mainly from industrial wastewater, domestic sewage, the combustion of petroleum and biomass, fishing activities, and petroleum spillage. Moreover, critical research gaps and recommendations for future studies on the occurrence, distribution, and ecological risk of organic pollution in mangroves were proposed. To the best of our knowledge, this review provides the occurrence, fate, ecological risks, influencing factors and recommendations of organic pollutants in mangrove sediment, offering a theoretical foundation and valuable reference for scientists, policymakers, and environmental managers aiming to develop more effective restoration and conservation techniques for mangrove ecosystems.