The present work was done together with PGAGEM – National Program of the Medical Geology and Environmental Geochemistry Research of CPRM - Geological Survey of Brazil, on the 1:250.000 that took place in northeast of the Pará State and the northwest of Maranhão State. This study focused on the Belém Sheet SA.22-X-D, on the same scale. With regional approach, 74 drainage basins with around 100km² were sampled for water and stream sediments. These were analyzed for 33 and 53 elements respectively in order to understand the distribution pattern on the environment. Some points of the public water distribution supply systems where also studied. The water samples were maintained by refrigeration and analyzed by ICP-OES in the LAMIN laboratory of CPRM in Rio de Janeiro. Physiochemical parameters such as pH, conductivity, dissolved oxygen, salinity and temperature were measured in situ. The stream sediments samples were collected in various points of the drainage (composed sample), and analyzed at Acme Laboratory using three different analytical methods: hydret generation connected to ICP-OES, for As and Se; mercury vapor generation connected to atomic absorption spectroscopy – CVAAS for Hg and ICP-OES for the others elements. To all the geochemical maps generated for the water samples was added the curve of maximum allowed concentration for the CONAMA/ Brazilian Health Ministry/WHO. It was also possible to define on the opposite margins of the Guamá river two regions with contributions from distinct source areas. On the south portion the primary source area is the Barreiras Formation. On the north portion, the primary source area are sands so called “post Barreiras” from the Pleistocene and submitted to intense lixiviation, with grades always below the background values, where the totality of the original rock elements was removed. The comparison of water and stream sediments results from the same point shows that the migration of the elements from the sedimentary rocks to the water, with pH values varying from 3.6 to 5.5, is a process actually working. More detailed isotopic studies must be done to confirm that despite smaller grades in the right margin, right on the more populated region of Belém city, these grades are anthropogenic, mainly for Pb and Cu. The data of PGAGEM Project for the public water distribution supply systems was reevaluated. Areas of high concentration and time of exposure were indicated using an expression called the Exposition Grade, the product of the concentration of a chemical element times the daily average ingestion of water (two liters) times the time of exposure. The Exposition Grade Factor defined the localities of Barcarena, Vila dos Cabanos and Moju (located in Belém Sheet), as 3 among 10 localities submitted to the highest exposure risk in all the PGAGEM area. It introduces the concept of ample and restrict geogenic anomaly. The first refers to the natural distribution pattern of elements on the environment. The second refers to both anthropogenic and natural distribution. Twelve basins where detected with ample geogenic anomalies for Al, B, Cu, Fe and Pb, and restrict geogenic anomalies for Cd, Co, Cr, F and Hg. These results are presented on the Geochemical Orientation for the Territorial Management and Public Health Map. This work generated a Geochemical Atlas of the continental portion of the Belém Sheet 1:250.000 scale with analytical results tables and over one hundred geochemical maps. This work confirms that regional and multi-element geochemical surveys outline the distribution patterns of the chemical elements in Nature, and therefore may predict and explain human health problems due to natural factors. This kind of study turns out to be a very useful tool in preventive implementation of Health and Territorial Management public policies.
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