RHIZOPHORA MANGLE as a Bioindicator of Environmental Exposure to Heavy Metals in the Navachiste Lagoon Complex, Sinaloa, Mexico

The objective of this work was to analyze the potential of Rhizophora mangle as a bioindicator of seven heavy metals, Fe, Cu, Zn, Mn, Ni, Cr, and Cd, in the mangrove sediments of the Navachiste lagoon complex (NAV). The concentration of trace metals (TM) in sediments and tis-sues (leaf, stembark, and root of R. mangle) were determined by digestion with nitric acid (HNO3), whereas the metal absorbance was measured by atomic absorption spectrophotometry with an air-acetylene flame. The enrichment factor, the bioavailable fraction, the seasonal varia-tion of heavy metal concentrations and their correlation with those determined in R. mangle tissues were assessed. Metal concentrations found in sediments were as following: Fe>Mn>Zn>Cr>Ni>Cu>Cd, and for tissues: Mn>Fe>Zn>Cu>Cr>Ni>Cd, and regarding the roots, the findings were as following: Fe>Mn>Zn>Cu>Cr>Ni>Cd. The highest trace metal concentra-tions were correlated with silt, clay, and organic matter in sediments with basic pH. The highest salinities were found adjacent to R. mangle trees. Of all the trace metals analyzed, there was only a positive linear regression between the bioavailability of Mn in the sediment with the concen-tration of Mn in leaf tissue consistently throughout the year. The Cu bioavailability in the sedi-ment showed similar positive linear regressions except for winter, where it did not show this pattern. These results suggest that the concentrations of Mn and Cu in the R. mangle leaf could be a potential bioindicator of environmental exposure to anthropogenic sources of contamination by these trace metals in sediments