Effect of the Long-Term Application of Sewage Sludge to A Calcareous Soil on Its Total and Bioavailable Content in Trace Elements, and Their Transfer to the Crop

Armelle Zaragüeta,Rodrigo Antón,Alberto Enrique,Henar Urmeneta,Iñigo Virto,Luis Orcaray

doi:10.3390/min11040356

Abstract

Sewage sludge (SS) can be used as an organic amendment in agricultural soils, provided they comply with the relevant legislation. This use can incorporate traces of metals into the soil, which can cause environmental or human health problems. In the study period between 1992 and 2018 (26 years), it was observed that the use of SS as an organic fertilizer significantly increased the total concentration of Zn, Cu, Cr, Ni and Hg of this study between 55.6% (Hg) and 7.0% (Ni). The concentration of Zn, Cu, Pb, Ni and Cd extracted with DTPA, also increased between 122.2% (Zn) and 11.3% (Cd). In contrast, the Mn concentrations extracted with Diethylene Triamine Pentaacetic Acid (DTPA)were 6.5% higher in the treatments without SS. These changes in the soil had an impact on the crop, which showed a significant increase in the concentration of Zn, Cu and Cr in the grain, between 15.0% (Cr) and 4.4% (Cu), and a decrease in the concentration of Mn, Cr and Ni in the barley straw when SS was added to the soil between 32.2% (Mn) and 29.6% (Ni). However, the limits established by current legislation on soil protection and food were not exceeded. This limited transfer to the crop, is likely due to the high content of carbonates and organic matter in the soil, which limit the bioavailability of most of the trace metals (TM) in the soil. As a conclusion, we observe that the use of SS as an organic amendment increased the concentration of some TM in the soil, in its bioavailable forms, and in the crop.

Highlights

The total concentration of Ni in soil was significantly different between the treatments that had not received Sewage sludge (SS) and those that had received SS
The application of SS as a long-term organic amendment in the conditions of soil, climate, management and type of sludge studied here, caused an accumulation of total Zn, Cu, Cr, Ni and Hg in soil, of Zn, Cu, Pb, Ni and Cd in their bioavailable form extracted by Diethylene Triamine Pentaacetic Acid (DTPA) and of Zn, Cu and Cr in grain
A higher concentration of Mn extracted with DTPA, as well as a higher concentration of Mn, Ni and Cr in the straw was observed, in the treatments without SS amendment

Summary

Introduction

As a consequence of the urbanization and industrialization of urban environments, there is a growing generation of wastewater of domestic and industrial origin. This water must be treated to ensure an environmentally safe and economically viable final destination. This wastewater treatment is generally carried out in treatment plants, and involves a generation of sludge (sewage sludge, SS). In Spain, the annual generation of SS accounts for approximately 1,000,000 tons of dry matter, remaining stable in recent years, approximately 80% of which is used in agricultural soils [2]

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