Elementos terras raras, U, Th e elementos potencialmente tóxicos em agroecossistemas com uso de fertilizantes no nordeste do Pará

Abstract

The Amazon region is the last agricultural frontier in Brazil and the increasing demand for food and renewable energy sources has intensified the pressure on land use. The Pará state is one of the world's largest producers of oil palm and black pepper, being the mesoregion Northeast Paraense responsible for the annual production of 1,634,476 tons of oil palm, 39,577 tons of black pepper and 286,768 tons of oranges, which represents 97, 50 and 2% of the Brazilian production. The Amazon soils, to express the high agricultural potential, demand high rates of fertilizer application. However, the raw materials used in the production of agricultural inputs are also sources of soil contamination. Thus, studies that facilitate the understanding of the dynamics of rare earth elements (REEs) and other metals / metalloids in the region's soils are relevant. And, based on the premise that anthropic action, mainly through agricultural activities, has caused significant increases in the levels of these elements in soils, the objective was to evaluate (i) the REEs concentrations and other metals in Amazon agroecosystems of orange, oil palm and black pepper, with 26, 10 and 5 years of implantation, respectively; (ii) determine the contamination rates, such as the enrichment and bioaccumulation factors and; (iii) establishing / discussing relationships with soil properties. The results showed: (i) REEs are extremely correlated to soil pH; (ii) the europium (Eu) presented the largest bioaccumulation factor among the REEs; (iii) the activity concentrations of 238U and 232Th in soil with black pepper cultivation were higher than the world average of 238U (35 Bq kg-1) and 232Th (30 Bq kg-1) according established by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR); (iv) moderate enrichment factors (EFs) for Ba, Pb and Zn (2> EF <5) and significant for As and Cu (5> EF <20); (v) the following orders of bioaccumulation: oil palm - Cu> Zn> Hg> Ni> Ba> Co> As> Cr> Cd ≈ Pb; black pepper - Zn> Hg> Cu> Ba> Ni> Co> Pb >> As> Cr> Cd; orange - Hg> Ni> Ba> Zn> Co> Cu> As> Pb >> Cr> Cd. In this context, this is the first study evaluating the absorption of REEs by Amazonian crops of great importance for global markets. A relevant contribution to predict the accumulation of contaminants in soils resulting from anthropic activities, especially in regions of agricultural importance and environmental vulnerability such as the biome Amazon.