Summary
This long-term field study examined how municipal sewage sludge applications to agricultural soil influence the soil antibiotic resistome and mobile genetic elements over 22 years. The researchers found that annual sludge applications had a more pronounced impact on soil resistome than single past applications, through both direct introduction of sludge-derived ARGs and stimulation of intrinsic soil resistance genes. Considerable proportions of sludge-borne ARGs, particularly aminoglycoside and tetracycline resistance genes, attenuated following soil application, though direct transfer of ARG-rich sludge-specific genes to soil was also observed.
UK applicability
These findings are directly relevant to UK agricultural practice, as sewage sludge application to farmland is regulated but widespread. The results inform risk assessment for biosolids recycling schemes and suggest that annual or frequent sludge applications may pose greater resistome risks than historical single applications, informing future guidance on sludge application frequency and management.
Key measures
High-throughput quantitative PCR quantification of ARG abundance and composition (multidrug, β-lactam, MLSB, tetracycline, vancomycin, aminoglycoside resistance genes); MGE marker gene abundance; ARG and MGE attenuation rates following application
Outcomes reported
The study quantified antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in soils receiving different sewage sludge applications over 22 years. It measured how ARG composition, diversity, and abundance varied between control soils and sludge-amended soils, and compared the effects of past versus annual sludge application modes.
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