The ecological role of estuarine areas on organic matter storage is well known. However, the contributions of soil organic matter (SOM) quality and mineralogy as geochemical filters remain unclear. It requires further investigations in pursuit of contaminant retention understanding, such as mercury (Hg), one of the greatest threats to mangrove areas. We evaluated the highest Hg pollution case of the Brazilian mangroves to investigate the role of SOM and minerals composition in controlling this heavy metal fate. Soils were sampled from different forests: Laguncularia racemosa, coexistence of species, and Rhizophora mangle distributed along the Botafogo estuary. Redox potential (Eh), pH, electrical conductivity (ECe), SOM content, and granulometry were performed. Total mercury (THg) and its distribution were also determined. SOM was analyzed by the evaluation of its thermal stability and molecular composition, while mineralogy was investigated due to XRD and microscopy procedures. We identified a severe contamination, in which THg concentration achieved values up to 14.3 mg kg-1, 161-fold higher than the local background. Besides the distance from the source, THg variation along the contaminated forests was controlled by the natural heterogeneity of C groups provided by different species domains. It clearly generates different scenarios for Hg retention in estuarine areas, especially where Rhizophora mangle develops, considering their characteristics to release more refractory C, such as tannin and lignin, responsible for blocking this contaminant. Simultaneously, but with a lower contribution, pyrite (Fe sulfide) acted as a retainer, also controlling Hg fate on the soil.
Keywords: Coastal ecosystem; Fe sulfide; Heavy metal; Molecular composition; Pollution; Refractory C.
Copyright © 2025 Elsevier B.V. All rights reserved.
