Hydrochar as a One Health solution to mitigate antibiotic resistance genes from slurry in grassland soils

Antibiotic resistance genes (ARGs) represent a growing global health concern, with agricultural practices, particularly livestock slurry application, serving as major contributors to their spread in soils. This review evaluates hydrothermal carbonization derived hydrochar as a potential One Health strategy for reducing ARG prevalence in slurry amended grassland systems. We synthesize current evidence on how hydrochar's properties and interactions within slurry-soil-grassland environments can limit ARG persistence, including its capacity to bind genetic material, affect microbial populations, and alter soil conditions that influence resistance dynamics. Where direct evidence from hydrochar based studies were lacking, findings from analogous materials such as biochar in related agricultural systems were used to elucidate the likely properties and impacts of slurry-derived hydrochar when applied to grassland slurry systems. In doing so, we highlight the potential of hydrothermal carbonization technology to contribute to addressing several environmental challenges in temperate grassland systems, where slurry management represents a persistent concern. Broader ecological and practical implications, such as impacts on soil function, microbial diversity, and the sustainability of hydrochar production, are also considered. Overall, this review highlights the potential of hydrochar as a tool for limiting the dissemination of ARGs from agricultural slurry and emphasizes the need for further research to optimize its application within sustainable grassland management. By synthesizing current evidence and identifying critical knowledge gaps, we propose hydrochar as a promising One Health intervention in slurry-soil-grassland systems and outline key research priorities required to realize its full potential.