Long-term use of biosolids as organic fertilizers in agricultural soils: potentially toxic elements occurrence and mobility

Abstract

The presence of potentially toxic elements (PTEs) may hinder a more widespread application of biosolids in agriculture. At present, the European Directive 86/278/CEE limit the total concentrations of seven metals (Cu, Cr, Ni, Pb, Zn, Cd and Hg) in agricultural soils and in sewage sludges used as fertilizers but it has not taken into consideration the potential impacts of other emerging micropollutants that may be present in the biosolids as well as their mobility. The aim of this study was to evaluate the accumulation and mobility of 13 elements (including regulated metals and other inorganic species) in agricultural soils repeatedly amended with biosolids for 15 years. Firstly, three digestions programs using different acid mixtures were tested to evaluate the most accurate and efficient method for analysis of soil and sludge. Results demonstrated that sewage sludge application increased concentrations of Pb and Hg in soil, but values did not exceed the quality standard established by legislation. In addition, other elements (As, Co, Sb, Ag, Se and Mn) that at present are not regulated by the Spanish and European directives were identified in the sewage sludge, and significant differences were found between Ag content in soils amended with biosolids in comparison with control soils. This fact can be related to the increasing use of silver nanoparticles in consumer products due to their antibacterial properties. Results from the leaching tests show up that, in general, the mobility degree for both regulated and non-regulated elements in soils amended with biosolids was quite low (<10 %).

Transformation‐dissolution reactions partially explain adverse effects of metallic silver nanoparticles to soil nitrification in different soils

“…Furthermore, in soil, ionic Ag will adsorb onto the soil solid phase, resulting in lower Ag concentrations in porewater than in freshwater. This low mobility was also found in the long‐term studies just mentioned: Ag concentrations were below the limit of detection for 2 leaching tests performed on the sewage sludge–amended soils (Marguí et al ), and Ag was not found in enriched concentrations in the deeper soil layers (Yang et al ). It is, therefore, impossible to transfer conclusions regarding the risk of AgNPs or the occurrence of a nanoeffect from aquatic to terrestrial systems.…”

“…In Europe, the soil Ag concentration is expected to increase by 1.6 μg Ag kg −1 yr −1 in sewage sludge–amended soils (Gottschalk et al ). A long‐term field study in Spain found a doubling of the Ag level in a soil amended with sewage sludge for 15 yr compared with nonamended soil (Marguí et al ). In another study (Yang et al ) a clear accumulation of Ag in the surface layer was found in sewage sludge–amended soils; however, no AgNPs could be observed in these soil samples with transmission electron microscopy energy‐dispersive X‐ray spectroscopy (TEM‐EDX).…”

Biosolids and Sludge Management

“…There were slight increases in metals (Cd, Cr, Cu, Pb) with biosolids application, but the levels were still below levels of concern, and ecotoxicological assessment showed no significant adverse effects. The potential for increase in metals resulting from the long-term application of biosolids was also studied with similar results by Margui et al (2015). This study found only significant increases of Ag in soils amended with biosolids as compared to control soils, which they attributed to silver nanoparticles in consumer products as a likely culprit.…”

Effects of freezing–thawing and wetting–drying on heavy metal leaching from biosolids

“…Biosolids are the solid residues generated during wastewater treatment (Margui, Iglesias, Camps, Sala, & Hidalgo, ; Sharma, Sarkar, Singh, & Singh, ). Biosolids contain large amounts of nutrients and organic matter (Christodoulou & Stamatelatou, ; Greenhalgh et al., ; Nogueira et al., ) and are therefore a valuable soil amendment (Carbonell, Torrijos, Rodriguez, & Angel, ; Joo, Dello Monaco, Antmann, & Chorath, ; Torri, Correa, Renella, Vadecantos, & Perelomov, ; Waterhouse, Boyer, Adair, & Wratten, ).…”