Abstract
There are currently many devices and techniques to quantify trace elements (TEs) in various matrices, but their efficacy is dependent on the digestion methods (DMs) employed in the opening of such matrices which, although "organic", present inorganic components which are difficult to solubilize. This study was carried out to evaluate the recovery of Fe, Zn, Cr, Ni, Cd and Pb contents in samples of composts and cattle, horse, chicken, quail, and swine manures, as well as in sewage sludges and peat. The DMs employed were acid digestion in microwaves with HNO3 (EPA 3051A); nitric-perchloric digestion with HNO3 + HClO4 in a digestion block (NP); dry ashing in a muffle furnace and solubilization of residual ash in nitric acid (MDA); digestion by using aqua regia solution (HCl:HNO3) in the digestion block (AR); and acid digestion with HCl and HNO3 + H2O2 (EPA 3050). The dry ashing method led to the greatest recovery of Cd in organic residues, but the EPA 3050 protocol can be an alternative method for the same purpose. The dry ashing should not be employed to determine the concentration of Cr, Fe, Ni, Pb and Zn in the residues. Higher Cr and Fe contents are recovered when NP and EPA 3050 are employed in the opening of organic matrices. For most of the residues analyzed, AR is the most effective method for recovering Ni. Microwave-assisted digestion methods (EPA3051 and 3050) led to the highest recovery of Pb. The choice of the DM that provides maximum recovery of Zn depends on the organic residue and trace element analyzed.
Highlights
Organic residues were collected in municipalities of the states of Minas Gerais and São Paulo, and the following types of waste were analyzed: commercial compost (C.COM) (Passos, MG), garbage compost (G.COM), organic compost (O.COM), cattle manure (BOV) (Lavras, MG), quail manure (QUAI) (Lavras, MG), horse manure (HOR), chicken manure (CHIC) (Lavras, MG), swine manure (SWI) (Oliveira, MG), urban sewage sludge (SL1), industrial sewage sludge (SL2) and peat (PEAT)
The C.COM was derived from the composting of poultry manure and sugarcane bagasse; the O.COM originated from a previous stage of substrate manufacturing, composed of a mixture of decomposed pine bark, peat and manure; and the G.COM was produced from the composting of an organic matrix which had been separated from the solid residues of garbage processing units
For determination of Cd (Figure 1), the results indicate that the greatest recovery was obtained by the MDA method for seven residues (QUAI, HOR, CHIC; O.COM; sludge 1 (SL1), sludge 2 (SL2) and G.COM)
Summary
The aim of this study was to evaluate the effect of five DMs (EPA 3051, NP, MDA, AR and EPA 3050) on recovery of Fe, Zn, Ni, Cr, Cd and Pb contents in samples of manures, composts, peat and sewage sludges
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