Downward Movement of Potentially Toxic Elements in Biosolids Amended Soils

Silvana Irene Torri,Rodrigo Studart Corrêa

doi:10.1155/2012/145724

Abstract

Potentially toxic elements (PTEs) in soils are mainly associated with the solid phase, bound to the surface of solid components, or precipitated as minerals. For most PTEs, only a small portion is dissolved in the soil solution. However, there is an interest in following the fate of mobile PTEs in the environment, for a growing amount of evidence indicates that downward movement of PTEs may occur in biosolids amended soils, leading to groundwater contamination. Therefore, it is crucial to understand the factors that control the release of these elements after land application of biosolids, in order to overcome problems related to downward movement of PTEs in the soil profile.

Highlights

The treatment of municipal wastewater produces huge amounts of sludge
The term biosolid was officially recognized in 1991 by the Water Environment Federation (WEF) and refers to the organic solids that have received a biological stabilization treatment at the municipal wastewater treatment plant, to make a distinction from other types of sludges that cannot be beneficially recycled as a soil amendment
In a soil column study in which biosolids was applied on surface, Gascoet al. [26] reported a relatively strong negative relationship between clay content and total percentage of leached potentially toxic elements (PTEs), in agreement with the results reported by other authors who have described the influence of clay size fraction in metals retention [27, 28]

Summary

Introduction

The treatment of municipal wastewater produces huge amounts of sludge. This material consists of the solids that were originally present in the wastewater and/or new suspended materials originated as the result of wastewater treatment processes [1]. McBride et al [13] and Richards et al [14] indicated that downward mobility might occur in the field without a substantial increase in PTEs concentrations in the subsoil These conclusions were consistent with later research, which did not show significant increases in total PTEs concentrations below 30-cm depth in soil profiles despite the differences in biosolids application methods or soil properties [12, 15, 16]. Grolimund et al [18] proposed that mobile, colloidal particles could act as pollutant carriers and provide a rapid transport pathway, even for strongly sorbing PTEs. the annual export of trace metals from the surface layer usually represents a small fraction of the total amount added, the cumulative transport of these elements over a prolonged period of time may result in a substantial redistribution into the subsoil, with the risk of ground water contamination [19]. The aim of this review is to analyze the effect of different soil factors that determine the mobility of potentially trace elements into the subsoil in biosolids-amended soils

Texture

Organic Matter

Chemical Immobilization

Findings

Conclusions