The estuarine region of the Marapanim River, located in the northeast of the State of Pará, Eastern Amazonian, is rich in mangroves closer to coastal zone areas, from where crustaceans are extracted by the local population, for consumption and provisioning of neighboring cities. In general the mangroves sediments have the capacity to absorb heavy metals whether in the organic matter, loamy fraction or sulfide minerals. In order to contribute for the knowledge of the distribution of these metals through several compartments of the mangroves and man as final consumer of its products, grain size analysis, mineralogical determinations and whole chemical and trace element analysis were carried out in sediments, vegetation, crab and human hair in order to evaluate the transference of metals in the chain sediment-vegetation-crabman. Two transects with the collection of sediments, vegetation (leaves of Rhizophora mangle) and crabs (Ucides cordatus) were established. Human hair was collected in inhabitants around the periphery of the city of Marapanim and rivershore of the Marapanim River. Salinity, pH and Eh (mV) directly measured in sediments were in the field. Grain size analyses considered the sand, silt and clay fractions, and the mineral identification were carried out by XRD and SEM/EDS and whole sediment chemistry and trace element and heavy metal analyses were conducted by ICP-MS, ICP-OES, and AAS. The samples of vegetation leaves, crabs and human hair were also analyzed by those methods and the MO by humid way. Mangroves sediments are silt-loamy, constituted by quartz, kaolinite, illite, smectite, Kfeldspars, goethite, pyrite, jarosite and halite. Quartz, kaolinite and goethite, and some illite, come from weathered sediments of Barreiras Formation, as source area of mangrove sediments and smectite, pyrite, K-feldspars and jarosite have been formed inside of the deposited sediments, as authigenic minerals. Salinity and pH increase with depth, the positive values of Eh indicate the oxidation of Fe 2+ and S 2- found in the sulfide minerals and organic matter. A second zone is characterized by acid pH (average 6,5) and negative Eh values which preserves sulfides and organic matter. Mangroves sediments contain high contents of SiO2, Al2O3 and Fe2O3 that reflect their main minerals, quartz, kaolinite, smectite and pyrite, showing the close relationship to the Barreiras Formation and their soil-derived material. The expressive contents of Na, K, Ca, and Mg found mainly as K-feldspars, illite, smectite and halite reflect the marine contribution to mangrove environment. The bioavailability of the elements in mangroves sediments is low, in general below to 1% of the total concentration of each element, except for As that displays high bioavailability. The leaves of Rhizophora mangle concentrate Mg, Ca and P, besides Zn, Sr, Zr, As, and Hg. These values are inside the normal range found in non impacted environments and reflect their very low concentration in mangrove sediments and indirectly in the Barreiras Formation sediments. Crabs show that the largest concentrations of Fe, Al, Mg, and Si in the hepatopancreas of the females, whereas Ca, K and Na in the muscles of females, Zn concentrates either in the muscles of females or males, however, with higher concentration in the muscles of females. Se and As also concentrate on the hepatopancreas of males and females but, the hepatopancreas of males concentrates more Se and the females, As. The transference of the elements in the sediments to the plants can be seen through the biological absorption coefficient (BAC), and Hg is the one that accumulated in the leaf tissue the best. The BAC plant-crab shows high values for Fe that concentrates either in the hepatopancreas as of males or females; Zn in the muscles of males and Sr in muscles and hepatopancreas of females. The contents of Hg, Se and As in human hair are very low, below the limits recommended by WHO for environments without anthropic influence. The human hair “mineral analyses” indicate that the nutritious elements are in the normal range, in the same way for so called toxic and additional “minerals”(chemical elements). The data obtained in sediments, in leaves and in crabs of the mangroves of Marapanim, show that leaves of Rhizophora mangle and crabs picture the chemical nature and indirectly the mineralogy of the mangrove sediments, and they reveal low values of transference of the chemical composition of the sediments to mangroves leaves to the crabs. The chemical composition of the sediments of the mangroves of Marapanim allows visualizing its affinity with the sediments of the Barreiras Formation, as source area, with a parge marine contribution, and it indicates that the mangroves, in fact don't present any natural geochemical anomaly nor indications of environmental impact. Thus crabs are important in the alimentary diet of the Marapanim region, constituting are appropriate food source because it doesn't present any evidence of contamination by heavy metals.
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