Summary
This long-term field study examined how municipal sewage sludge applications to agricultural soil influence the soil resistome and mobile genetic elements. Using high-throughput quantitative PCR on soils receiving past or annual sludge applications since 1994, the researchers found that annual applications had a more significant impact on soil resistome through both continued introduction of sludge-derived ARGs and stimulation of soil intrinsic resistance genes, with considerable attenuation of sludge-specific genes (particularly aminoglycoside and tetracycline resistance) following soil incorporation. The findings suggest sewage sludge recycling represents a pathway for dissemination of urban antibiotic resistance from wastewater into agricultural systems.
UK applicability
These findings are directly applicable to United Kingdom practice, where sewage sludge application to agricultural land is regulated under the Quality Protocol for the Use and Disposal of Quality Protocol for the Use and Disposal of Sewage Sludge on Land. The study provides evidence relevant to UK environmental risk assessment and policy regarding sludge recycling, suggesting that frequency of application (annual versus episodic) meaningfully affects soil resistome burden.
Key measures
High-throughput quantitative PCR quantification of ARGs (multidrug, β-lactam, MLSB, tetracycline, vancomycin, aminoglycoside resistance genes) and MGE marker genes in soil and sewage sludge samples
Outcomes reported
The study quantified antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soils receiving different sewage sludge application regimes over a 22-year period. It measured the composition, diversity and abundance of soil resistome markers and tracked how ARG profiles differed between sludge sources and soil environments.
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