Are mangroves and lagoons safe? A global assessment of PAH pollution, sources, and ecological risks

Coastal mangroves and lagoons frequently receive substantial inputs of polycyclic aromatic hydrocarbons (PAHs) from urban runoff, industrial emissions, and oil spills. This review analyzes PAH accumulation in mangrove and lagoon ecosystems worldwide from 2000 to early 2025, based on over 42 articles published during this period. PAH hotspots were observed in water from the Porto-Novo Lagoon (Benin, 3.88 × 10⁷-1.24 × 10⁸ ng L^-1) and in sediments from the Sundarbans mangrove wetland (India and Bangladesh, 4880-20 000 ng g^-1). Over the past 25 years, levels of the 16 priority PAHs have increased in the Sundarbans but decreased in Fugong mangrove sediments (China). Source apportionment indicated dominant pyrogenic inputs in Lagos Lagoon (Nigeria) water during both wet and dry seasons, and contributions from diesel exhaust (47.2%), coal combustion (17.4%), and oil spills (35.4%) in Estero de Urías Lagoon (Mexico) sediments. In mangroves of Shenzhen (China) and along the Red Sea coasts of Egypt and Saudi Arabia, PAH concentrations were higher in leaves than in roots or surface sediments, while in Hainan (China), PAHs were also detected in mangrove fruits. In the Bodo mangroves (Nigeria), PAHs were found in tipalia (Tilapia guinensis and Sarotherodon melanotheron) and swimming crabs (Callinectes amnicola). Broader investigations across fish species and mangrove-lagoon food webs are needed. These ecosystems perform crucial ecological and economic functions, including coastal protection, sediment stabilization, and nutrient cycling. This review provides a global synthesis of PAH distribution, sources, and temporal trends, establishing a foundation for future monitoring, risk assessment, environmental policy, and research priorities in organic geochemistry.