Heavy metals extractability in a soil amended with sewage sludge

Abstract

Few investigations have been carried out about the comparison of desorption rate and amount of heavy metals extracted successively by organic acid mixtures mimicking the rhizosphere and routine extractants in sewage sludge-amended soils. Extractions of Zn, Cd, Ni, Cr, and Cu were performed in samples of a sewage sludge-amended soil using seven extractants: four organic acid mixtures and three routine extractants (DTPA, Mehlich-I, and ammonium acetate). Results from single pass extractions, in which the extractable metal contents were determined by simply extracting the soil a single time, as well as from 15 successive extractions, in which the solid residues of the first extraction was successively extracted 14 additional times, of heavy metals were analyzed. The extractability of heavy metals in a single pass extraction was, in general, as follows: Mehlich-I > DTPA > organic acids > NH 4 OAc. The highest rates of extraction followed the general order: DTPA > Mehlich-I > organic acids > NH 4 OAc. While Mehlich-I presented the highest extractability of heavy metals among studied extractants, DTPA showed a high extractability of Zn, Cd, Ni, and Cu in a single extraction as well as the highest rates of extraction among the studied extractants. The transfer of heavy metals from soil to organic acid solutions is slower than to DTPA and Mehlich-I extractants. Key words: Oxisol, extraction rate, trace elements EXTRACTABILIDADE DE METAIS PESADOS EM UM SOLO TRATADO COM LODO DE ESGOTORESUMO: Poucos trabalhos têm sido realizados sobre a comparação da taxa de dessorção e da quantidade de metais extraídos sucessivamente por misturas de ácidos orgânicos que imitam a composição da rizosfera e por extratores usados na rotina em amostras de solo tratado com lodo de esgoto. Extrações de Zn, Cd, Ni, Cr e Cu foram realizadas em amostras de um solo de carga variável tratado com lodo de esgoto usando-se sete extratores: quatro misturas com ácidos orgânicos e três extratores usados na rotina (DTPA, Mehlich-I e acetato de amônio). Os resultados para uma única extração, em que o conteúdo de metais extraíveis foi determinado simplesmente extraindo-os do solo uma única vez, bem como após 15 extrações sucessivas, em que o resíduo sólido da primeira extração foi extraído sucessivamente por mais 14 vezes, foram analisados. A extractabilidade dos metais em uma extração simples foi, em geral, como segue: Mehlich-I > DTPA > ácidos orgânicos > NH 4 OAc. As mais elevadas taxas de extração seguiram a ordem: DTPA > Mehlich-I > ácidos orgânicos > NH 4 OAc. A maior extração de metais foi obtida com Mehlich-I, enquanto, o DTPA também extraiu alta quantidade de Zn, Cd, Ni e Cu em uma extração simples, bem como obteve as mais altas taxas de extração entre os extratores estudados. A transferência de metais do solo para as soluções de ácidos orgânicos foi mais lenta que para os extratores DTPA e Mehlich-I. Palavras-chave: Latossolo, taxa de extração, elementos-traço

Heavy Metal Phytotoxicity to Radish (Raphanus sativus L.) in a Digested Sludge-amended Gangetic Alluvium

“…He and Singh (1993) assigned increased extractability of Cd by DTPA to decrease in pH caused by decomposition of sludge-borne organic matter. Among seven extractants (DTPA, Mehlich-I, NH 4 OAc, and four organic acid mixtures) studied by Marchi et al (2009), DTPA presented a high extractability of Cd and Ni as well as the highest rates of extraction in a soil amended with sewage sludge. Despite higher total Cr levels than the total Pb levels in the experimental sludge, the extractability of Cr by DTPA was much lower than that of Pb at all rates of sludge application.…”

Leachability and Vegetable Absorption of Heavy Metals from Sewage Sludge Biochar

“…While there are numerous studies that deal with sorption capacity of biochars for heavy metals when applied to soil in light of phytoremediation perspective (Cao et al, 2009;Namgay et al, 2010;Uchimiya et al, 2011), studies regarding on leachability (through desorption or dissolution) of heavy metals from biochar and their bioavailability are virtually nonexistent. The heavy metals, however, are known to be desorbed by naturally occurring organic acids such as citric, oxalic, acetic, and lactic acids (Nascimento, 2006;Marchi, 2009) and dissolved organic carbon (Antoniadis & Alloway, 2002) from soils amended with sewage sludge. Regardless of equilibrium amounts of Cd adsorbed in an Andisol, more than 80% of Cd was desorbed with one time extraction with citric acid if its concentration was more than 0.1 M, and more than 90% was recovered if five soil pore volumes of 0.1 M citric acid were continuously run through the Cd-contaminated soil (Abe et al, 2004).…”

Trace Elements in Biosolids‐Amended Soils

“…Marchi et al [81] compared the amount of elements extracted from biosolids-amended soils by four organic acid mixtures that mimic the compositions of organic acids in the rhizosphere and three reagents commonly used for trace element extraction, namely DTPA-TEA [73], Mehlich-I [77], and ammonium acetate [82]. They showed that the one-time extraction did not remove all of the extractable elements in the soils.…”