The Maracanã estuary is located in the northeastern of Pará State, within the Extraction Marine Reserve (Law 9.985/00), which has as primary goal to the sustainable use and conservation of the renewable ressources, protecting living conditions and the culture of the population, which consists of fisherman, small seliers and the local community. Due to its environmental characteristics, this area represents an important pole for the regional development. In this work, one of the aims was to search a geochemical formality to an interpretation of analytical results related to the geochemistry of the superficial sediments of the estuary of Maracanã bottom in order to determine the amount of heavy metais (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) of the granulometry with smaller fractions than 0,64 tem by atomic absorption spectrometry, to obtain the current inexistent background leveis. In the Maracanã estuary, it was registered much more silt-clay fraction than sand fraction, besides mineralogical similarity that indicates presence of kaolinite, illite and smectite. The amount of organic matter (MO) (5,4±0,70%) in sediments was homogeneously distributed. The pH didn't vary much, only between weakly acid (6,48) and weakly alkaline (7,13). Heavy metais - 1) in Maracanã river estuary cadmium concentrations were under of the equipment detection limit (0,009 ppm); 2) Cobalt varied from 46 to 55 ppm (50,97 ± 2,31 ppm) in total fraction, and from 5 to 7 ppm (6 ± 0,37 ppm) in bio-available fraction; 3) Cromo varied from 126 to 152 ppm (140,33±6,56 ppm) in total fraction and from 17 to 24 ppm (20,73±1,7 ppm) in bio-available fraction; 4) Copper varied from 17 to 21 ppm (18,97±1,19 ppm) in total fraction and from 6 to 9 ppm (7,0 ± 0,69 ppm) in bio-available fraction; 5) Iron varied from 3,4 to 4,6 % (4,14± 0,24 %) in total fraction and from 1,5 to 1,9 % (1,66± 0,1 %) in bio-available fraction; 6) Manganese varied from 293 to 545 ppm (423,53±74,63 ppm) in total fraction and from 168 to 499 ppm (335,1±91,3 ppm) in bio-available fraction; 7) Nickel varied from 44 to 53 ppm (48,77 ± 2,27 ppm) in total fraction and from 7 to 9 ppm (8,03±0,56 ppm) in bio-available fraction; 8) Lead varied from 42 to 48 ppm (45,63±1,69 ppm) in total fraction and from 14 to 17 ppm (15,13±0,78 ppm) in bio-available fraction; 9) Zinc varied from 72 to 85 ppm (78,83±3,44 ppm) in total fraction and from 26 to 32 ppm (29,43±1,65 ppm) in bio-available fraction. Concentration values of the bio-available heavy metal analyzed are smaller than those VGQS (Guide-Value of Sediment Quality), established by the "Canada Environmental Agency" (AAC) and the "National Oceanic and Atmospheric Administration"(NOAA), indicating that it should rarely occur bad effect on local biota. Considering that the area is an extraction reserve and that were not found evidence of anthropic contamination associated with the heavy metais, neither in their total fractions nor in their bio-available fractions in the Maracanã estuary, it is possible to consider that the data obtained from both analyzed geochemical fractions of heavy metais represent a value dose to the characteristical background of the region. Therefore, the Maracanã estuary is a reference cite to study the biogeochemistry and ecotoxicoiogy of the sediments of similar environments in Coastal of the Pará State. Besides that, the data obtained in this work can provide a subside for future geochemical and environmental surveys in the area, once that concentration ranges and reference values for many heavy metais that are present in the bottom sediments of this estuary were established.
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