Quality assessment of soils requires knowledge of distinct pollutant sources and process that leads the enrichment of harmful substances, by natural or anthropogenic causes. Reference values to chemical substances contents are used to characterize polluted or contaminated areas based preliminarily on background values. A background value refers to the natural concentration of an element or a substance in soils that have not been modified by anthropogenic activities aspects impacts. The establishment and distinction of these contents from different sources, regarding their strict reference values, guides normative instructions and some environmental laws in several countries, establishing the classification of areas with distinct levels of contamination. Decreasing soil quality by means of contamination and pollution by heavy metals is nowadays recognized as a serious risk for environmental quality and to the human health. Thus, the study goal consists in a reflection about the mineral nature of soils (reference values) and anthropic input in areas under pressure from agricultural frontiers, using as a case study the Southwest region of Amazonia. The study also proposes a comparison with the current situation in Europe, in order to subsidize the elaboration of public policies for the region under pressure of agricultural use in Brazil. In southwestern region of Brazilian Legal Amazon region, the land use is facing a continuous transformation, from mining activities and wood extraction to agricultural practices with intense use of fertilizers. These practices contribute with great volumes of heavy metals added to a weak tropical soil in this frontier region, characterized by land use conflicts between areas of indigenous reserves, farmlands and illegal mining activities. This work deals with the state of the art of legislation and proposals for reference values of some harmful substances suitable to the region and a preliminary delineation of conditions and vectors that allows their expansion. In this protective sense, intergovernmental actions aiming the control of pollution by heavy metals, particularly Cadmium, among other chemical components, pointing to a more restricted use of phosphate fertilizers, rich in heavy metals, are recommended in several countries of the European community. European reference values are compared to the values practiced in Mato Grosso e Rondônia States, Brazil, as well as an analysis of several procedures to obtaining the reference values.