Ygor Jacques Agra Bezerra da Silva

Comparison of USEPA digestion methods to heavy metals in soil samples

The use of appropriate analytical methods is of paramount importance for risk assessment and monitoring of potentially toxic metals in soils. In this sense, the objective of this study was to compare the effectiveness of two sample digestion methods, recommended by the Brazilian legislation for the management of contaminated areas (CONAMA 2009), aiming at the determination of environmentally available metal concentrations (USEPA 3050B, USEPA 3051A), as well as a total digestion method (USEPA 3052). Samples from 10 classes of soils were analyzed for Cu, Zn, Cd, Pb, Ni, and Hg. The results showed that the USEPA method 3051A is more efficient than the USEPA method 3050B in the extraction of levels considered environmentally available of Zn, Cu, Cd, Pb, and Ni. Besides providing a higher recovery of these elements, the method requires shorter digestion time, lower consumption of acids, and reduced risk of contamination. The USEPA method 3051A showed greater efficiency in Hg extraction in soils with higher clay content. Therefore, it is suitable for situations where a wide range of soils with different mineralogical characteristics are analyzed or in order to decrease the losses due to volatilization of the element in open systems.

COMPARISON OF DIGESTION METHODS TO DETERMINE HEAVY METALS IN FERTILIZERS

The 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.

Atriplex nummularia Lindl. as alternative for improving salt-affected soils conditions in semiarid environments: a field experiment

3 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 76(1) JANUARY-MARCH 2016 3 ULY-SEPTEMBER Atriplex nummularia Lindl. represents a cost-effective alternative for improving salt-affected soils in arid and semiarid environments due to its high adaptability to salinity and water deficiency. This study aimed to investigate soil physical-chemical changes in response to A. nummularia cultivation under field condition. Additionally, we quantified its biomass yield and phytoextraction potential. Two treatments were evaluated: soil cultivated with Atriplex under two crop densities (1 × 1 and 2 × 2 m), and a control (bared soil) with four replicates. The samples were taken at three soil depths (0-5, 15-20, and 40-45 cm). In general, dry biomass yield for leaves, stems and roots, as well as the bulk density and the hydraulic conductivity of the soil were sensitive to crop densities. Thus, the use of A. nummularia can be recommended for phytoremediation of salt-affected soils, as well as to improve soil physical condition. When it comes to salt phytoextraction per area, we recommend planting A. nummularia at a 1 × 1 m crop density. The greater accumulation of salts was observed in leaves, as observed for Na (82% roughly). However, in order to improve soil physical conditions, we suggest the management of A. nummularia under 2 × 2 m crop density. Pruning was fundamental to increase the biomass yield and, consequently, the phytoextraction of specific ions, e.g., Na, Cl. It was responsible for 83% and 88% of the total dry biomass at 1 × 1 and 2 × 2 m crop density, respectively.