Use of sequential extraction to assess the influence of sewage sludge amendment on metal mobility in Chilean soils

Abstract

In Chile, the increasing number of plants for the treatment of wastewater has brought about an increase in the generation of sludge. One way of sludge disposal is its application on land; this, however involves some problems, some of them being heavy metal accumulation and the increase in organic matter and other components from sewage sludge which may change the distribution and mobility of heavy metals. The purpose of the present study was to determine the effect of sewage sludge application on the distribution of Cr, Ni, Cu, Zn and Pb in agricultural soils in Chile. Three different soils, two Mollisols and one Alfisol, were sampled from an agricultural area in Central Chile. The soils were treated with sewage sludge at the rates of 0 and 30 ton ha(-1), and were incubated at 25 degrees C for 45 days. Before and after incubation, the soils were sequentially extracted to obtain labile (exchangeable and sodium acetate-soluble), potentially labile (soluble in moderately reducing conditions, K4P2O7-soluble and soluble in reducing conditions) and inert (soluble in strong acid oxidizing conditions) fractions. A two-level factored design was used to assess the effect of sludge application rate, incubation time and their interaction on the mobility of the elements under study. Among the metals determined in the sludge, zinc has the highest concentration. However, with the exception of Ni, the total content of metals was lower than the recommended limit values in sewage sludge as stated by Chilean regulations. Although 23% of zinc in sludge was in more mobile forms, the residual fraction of all metals was the predominant form in soils and sludge. The content of zinc only was significantly increased in two of the soils by sewage sludge application. On the other hand, with the exception of copper, the metals were redistributed in the first four fractions of amended soils. The effect of sludge application rate, incubation time and their interaction depended on the metal or soil type. In most cases an increase in more mobile forms of metals in soils was observed as the final effect.

Distribution of different fractions of Iron, Zinc, Chromium, lead and Nickel in Soils around Petrol filling stations in selected Areas of Delta State, Nigeria

“…The metals bound to this fraction are assumed to stay in the soil for longer period but may be immobilized by decomposition process (Kenedy et al, 1997). The metal forms associated with organic matter could be considered potentially active or strongly bound, depending on the physical properties of the soil (Ahumadu et al, 2004, Jamali et al, 2007, Kabirineja et al, 2014. Tessier et al, (1979), suggested that under oxidizing conditions, in natural waters, organic matter can be degraded, leading to a release of soluble trace metals.…”

Distribution of Cd, Ni, Cr, and Pb in Amended Soils from Alicante Province (SE, Spain)

“…This indicates that Cr is tightly bound in the matrix and would not be easily release under natural conditions (Ahumada et al 2004;Karathanasis and Johnson 2006). The residual fraction was the main Cr fraction in the calcareous soils (75-85%) and in soil 1 (>50%), with a very high percentage in this phase.…”

“…In soil 1, there are an important percentage of metal as soluble-exchangeable phase and as reducible phase. This soil has a pH=6.5 and chromium was mainly Lead is one of the least concentrated elements both in the soils and in the sludge and, the same as other metals, it is predominantly found in the residual fraction (Ahumada et al 2004). The main fraction for Pb in calcareous soils was the residual phase (65-90%).…”

Fate of biosolids Cu and Zn in a semi-arid grassland

“…specifically adsorbed/carbonate-bound) phases. Ahumada et al (2004) noted that 23% of biosolids-borne Zn was present in mobile forms, yet the residual fraction was the predominant form in biosolids-amended soil. Regardless, given time the specifically adsorbed/carbonate-bound phase should transformed to more resistant phases within the soil surface.…”

“…Guerra et al (2007) incubated soils treated with 30 Mg ha À1 biosolids for 60 days, observing an increase in Cu associated with the organic matter fraction. Ahumada et al (2004) treated several soils with 30 Mg biosolids ha À1 and showed that biosolids increased Cu in the stable residual phases.…”