Molecular and trace metal signatures of pristine and anthropogenically altered mangrove sediments

Mangroves contribute to long-term carbon sequestration and are considered as blue carbon ecosystems; however, they are facing increasing anthropogenic pressures, with trace metals emerging as an environmental concern. Despite their toxicological impacts, the mechanisms governing trace metal retention in mangrove sediments require further investigation, particularly their association with natural organic compounds. Here, we employed Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) to analyze a wide range of lipids in mangrove sediments from two pristine sites and one anthropogenically disturbed site collected in the Leizhou Peninsula (South China). Our study reveals distinct molecular fingerprints of lipids between these ecosystems: (i) pristine mangroves contain a higher proportion of biologically recalcitrant and aromatic compounds, while (ii) anthropogenically disturbed mangroves show a greater prevalence of biologically labile compounds potentially linked to sewage contamination. Mercury (Hg) was found to be particularly associated with more biologically labile and less aromatic lipids, whereas other trace metals, such as chromium (Cr), zinc (Zn), arsenic (As), and lead (Pb), are preferentially associated with biologically recalcitrant and aromatic lipids. One possible interpretation is that lipidomic profiles and their binding capacities for these trace metals differ among mangrove ecosystems, allowing them to retain distinct trace metals, and vice versa. Such potential lipid-metal interactions still need to be verified through future experimental binding studies or speciation analyses across broader geographic areas. This work has potential implications for understanding the fate of trace metals and organic matter in mangrove ecosystems and for developing sustainable management strategies.