Abstract
PurposeSewage sludge land application is strongly recommended to improve soil quality and fertility despite the presence of pollutants, pathogens and antibiotic resistance genes. This study aimed to assess the fertilization value of low and recommended by law sewage sludge dose (15 t ha−1).Materials and methodsIn a 540-day field study, the effect of sewage sludge on the soil physicochemical and microbial parameters, emphasising antibiotic and metal resistance spread, was investigated.ResultsIn contrast to expectations, sewage sludge did not improve the organic matter, nutrient content and microbial activity in the soil; therefore, the fertilization effect was not achieved. Moreover, an increase in the bioavailable Cd, Ni and Cu content was observed. Canonical correspondence analysis revealed that these increases mainly explain the changes in the soil microbial community. Sixteen resistance genes and four integron classes were detected in both the total DNA and on plasmids isolated from sewage sludge. Obtained plasmids confer β-lactam resistance or extreme resistance to tetracycline (> 256 μg mL−1). Two antibiotic resistance genes (blaNPS-2, tetA) were transferred into the fertilized soil and detected up to 6 months after the fertilization.ConclusionOur results provide evidence that the regulated dose of sewage sludge, even when characterized by low total metal content, may affect soil microbial microbiome and resistome. Therefore, these findings provide critical data that have public health implications, which may raise concerns about the suitability of applying sewage sludge to the soil even at the low regulated dose.
Highlights
Responsible editor: Jizheng HeOver the past several decades, sewage sludge land application was strongly recommended to improve soil quality and productivity, reduce the need for chemical fertilizers and solve waste disposal problems (European Commission 2014; Mininni et al 2015)
The sewage sludge had an alkaline pH (8.08), and its application caused only a temporary and slight increase (p < 0.05) in the pH value in the FS on day 1 compared to the control unfertilized soil (CS) (Table 2, Fig. 1)
The presence of the integrase genes detected in the sewage sludge DNA and on the plasmids isolated in our study indicates the prevalence of integrons in sewage sludge bacteria (Makowska et al 2016; Jang et al 2018)
Summary
Over the past several decades, sewage sludge land application was strongly recommended to improve soil quality and productivity, reduce the need for chemical fertilizers and solve waste disposal problems (European Commission 2014; Mininni et al 2015). Sewage sludge is a source of organic matter and several nutrients for plants, especially nitrogen, phosphorus, calcium, magnesium and potassium (Seleiman et al 2013). Despite substantial nutrient content in sewage sludge, its land application can only partially replace industrial fertilizers. To ensure a reasonable amount of plant essential mineral elements and organic matter in the fertilized soil, unrealistic high amounts and annually repeated sewage sludge application is a common practice (Hamdi et al 2019; Urra et al. Journal of Soils and Sediments (2021) 21:2882–2895
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