REFERENCE VALUES OF THE HEAVY METALS NATURAL CONCENTRATIONS IN SOILS OF THE CENTRAL AMAZON

Considering the size of the Amazon region and the need for studies to establish soil trace metal concentrations in natural environments, the objective of this work was to evaluate heavy metal contents in a toposequence of an Amazon State microbasin. Soil samples were collected in three native forest topographic positions. Samples were opened for analysis by two methods: exchangeable cations were determined by the silver thiourea method and total metal elements by sulfuric acid. The metals were determined by atomic absorption spectrometry. In general, it was observed low concentration of several elements considered essential to plant growth in the studied soils, indicating low concentration in the source material of these soils and the intense weathering leaching. The higher concentrations of heavy metals found in the Plateau / Shed areas may be related to clay soils and more acidic pH than other topographies. Exchangeable Al was found at higher concentrations, while Na was the element with the lowest concentration. Total metallic elements presented higher availability potential in the Plateau / Shed areas, except for B, Cr, Mo and Ni. These differences justify the development of regionalized studies for heavy metals in soils appropriate to the conditions of each environment.