Polycyclic aromatic hydrocarbons (PAHs) pollution in mangrove ecosystems: global synthesis and future research directions

Although coastal ecosystems such as mangroves have substantial productive and protective rules, this ecosystem is threatened due to inorganic and organic contaminants including polycyclic aromatic hydrocarbons (PAHs). PAHs are lipophilic, persistent, carcinogenic, mutagenic and considered as a global concern. We reviewed the occurrence, distribution and sources of PAHs in the mangrove ecosystem, providing a comprehensive discussion on this information and giving recommendations for future research. Through systematic literature search, this review considered existing studies on PAHs in the different compartments (water, sediment, aquatic fauna and plants) of mangrove system collected from field investigations. Little information is available for the levels and sources of PAHs in the water compartment of the mangrove systems. PAHs in the mangrove sediments are reported for 18 countries, and most of the levels of PAHs in mangrove sediments are considered as being low (0—100 ng g⁻¹ dry weight, DW) to moderate (100–1000 ng g⁻¹ DW). Different diagnostic ratios have been applied in order to determine the potential source of PAHs in the mangrove sediments, that are mainly attributed to mixed sources (pyrogenic and petrogenic). Studies have documented the biomonitoring of PAHs in mangrove systems, the majority of which use bivalves. Additionally, there are published studies for PAHs levels in 12 species of mangrove plants; showing a general tendency of residual PAHs accumulation in the leaves, if compared to root samples (leaves > roots). As a result of atmospheric PAH accumulation in leaf surfaces, leaves have higher concentrations of PAHs; implying that mangrove leaves can be used to monitor air quality relative to PAH pollution in coastal environments. This review has implications for future research in this field as well as coastal environmental management.

Graphical abstract