Exploring VA presence in groundwater of densely populated livestock farming watersheds: Sources, seasonal dynamics and geospatial relationships

Antibiotics are an indispensable component of the livestock industry and are released into the environment through various pathways during livestock rearing processes. Among various environmental mediums, groundwater holds significant importance as it serves as a crucial resource for potable water supply and agricultural practices. However, the persistent use of antibiotic-contaminated groundwater can lead to prolonged exposure to these agents in human and ecological systems, thereby engendering serious apprehensions, including the emergence of antibiotic-resistant bacterial strains. Therefore, in this study, the concentration of antibiotics in groundwater within densely populated livestock farming areas was analyzed using UHPLC-q-orbitrap HRMS combined with online solid-phase extraction. The measured cumulative concentrations of antibiotics in the groundwater samples collected from the surveyed areas ranged from 15.8 ng L─1 to 1530.0 ng L─1. The residual antibiotics obtained from the surveyed region exhibited significant seasonal variation, with higher concentrations observed during summer. This seasonal pattern is attributed to the combined effects of agricultural activities and climatic factors. The concentrations of antibiotics in the investigated area demonstrated associations between the composition of livestock species and the density of livestock farming facilities. Specifically, veterinary-specific antibiotics (sulfaquinoxaline [SQX] and clopidol [CLO]), commonly employed in poultry farming, were found to be more prominent in the area with a high concentration of poultry farming facilities. In regions characterized by a dense poultry farm presence, the highest concentrations of SQX and CLO were founded at 135.7 ng L─1 and 178.6 ng L─1, respectively. In contrast, areas without any farms exhibited lower concentrations, measuring 39.9 ng L─1 for SQX and 10.1 ng L─1 for CLO. Similarly, antibiotics primarily used in swine farming showed a strong correlation with the presence of large-scale swine farming operations. In the case of sulfamethazine, which is commonly used in pig farming, concentrations exceeding 500 ng L─1 were observed in groundwater samples collected near large-scale swine farming facilities. These observations suggest that antibiotics are introduced into groundwater through the discharge of wastewater and excreta from livestock farming facilities. Consequently, this study establishes that regional variations in antibiotic concentrations within groundwater are influenced by factors such as local usage patterns, the scale and types of livestock farming, and the prevailing climatic conditions. In order to elucidate the precise associations between multiple sources of contamination, including livestock farming facilities, and to enhance our understanding of their spatial correlations, there appears to be a need for research focused on spatial correlation analysis.