Comparison of digestion methods to determine heavy metals in fertilizers

Abstract

SUMMARYThe lack of a standard method to regulate heavy metal determination in Brazilian fertilizers and the subsequent use of several digestion methods have produced variations in the results, hampering interpretation. Thus, the aim of this study was to compare the effectiveness of three digestion methods for determination of metals such as Cd, Ni, Pb, and Cr in fertilizers. Samples of 45 fertilizers marketed in northeastern Brazil were used. A fertilizer sample with heavy metal contents certified by the US National Institute of Standards and Technology (NIST) was used as control. The following fertilizers were tested: rock phosphate; organo-mineral fertilizer with rock phosphate; single superphosphate; triple superphosphate; mixed N-P-K fertilizer; and fertilizer with micronutrients. The substances were digested according to the method recommended by the Ministry for Agriculture, Livestock and Supply of Brazil (MAPA) and by the two methods 3051A and 3052 of the United States Environmental Protection Agency (USEPA). By the USEPA method 3052, higher portions of the less soluble metals such as Ni and Pb were recovered, indicating that the conventional digestion methods for fertilizers underestimate the total amount of these elements. The results of the USEPA method 3051A were very similar to those of the method currently used in Brazil (Brasil, 2006). The latter is preferable, in view of the lower cost requirement for acids, a shorter digestion period and greater reproducibility.Index terms: soil contamination, soil pollution, chemical extraction. RESUMO: COMPARAÇÃO DE MÉTODOS DE DIGESTÃO PARA METAIS PESADOS EM FERTILIZANTESA ausência de normatização de um método-padrão para determinar os metais pesados em fertilizantes no Brasil e a consequente utilização de diversos métodos de digestão têm provocado variações nos resultados, dificultando a sua interpretação. Nesse contexto, o objetivo deste trabalho foi comparar a eficiência de três métodos de digestão de fertilizantes para delimitar os metais Cd, Ni, Pb e Cr. Foram utilizadas 45 amostras de fertilizantes comercializados no nordeste do Brasil, além de uma amostra de fertilizante com teores de metais certificados pelo National Institute of Standards and Technology (NIST), incluindo fosfato natural, fertilizante organomineral com fosfato natural, superfosfato simples, superfosfato triplo, fertilizante misto e fertilizante com micronutrientes, que foram digeridos pelos métodos do Ministério da Agricultura, Pecuária e Abastecimento (MAPA) e da Agência Americana de Proteção Ambiental (USEPA): 3051A e 3052. Os resultados demonstraram que o método USEPA 3052 apresentou maiores recuperações para metais menos solúveis, como Ni e Pb, evidenciando que os teores totais desses elementos são subestimados pelos métodos convencionais de digestão para fertilizantes. O método USEPA 3051A evidenciou resultados muito semelhantes ao método atualmente em uso no Brasil (Brasil, 2006), sendo preferido seu uso em razão da diminuição dos custos com ácidos, do menor tempo de digestão e ...

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