Changes of antibiotic occurrence and hydrochemistry in groundwater under the influence of the South-to-North Water Diversion (the Hutuo River, China)

The occurrence of antibiotics in groundwater has significant spatial variability, owing to the complexity of pollutant properties, pollution sources and groundwater recharge and discharge conditions. This study aimed to identify the relationship between antibiotic occurrence and hydrochemistry in groundwater. Thus, we undertook this study in a characteristic alluvial-diluvial aquifer where groundwater receives unidirectional recharge from surface water. In total, 47 samples were collected from the Hutuo River before and after an artificial replenishment project. We screened up to four classes of antibiotics and detected 28 types. The statistical analysis of antibiotic concentrations, indicated that there were two pollution areas. Next, we discussed the results pertaining to the occurrence and source of antibiotics by comparing them with hydrochemical data. In the study area, a positive correlation has been found between inorganic compounds, as SO₄²⁻ and Cl⁻, and the most mobile antibiotics given that both share the same source. This shows that a previous sound geochemical study may provide evidence of the extend of antibiotic occurrence, as in the Hutuo River aquifer. The relationship between antibiotics and hydrochemistry in groundwater is determined by recharge sources (rainwater and surface water contaminated with antibiotics). Antibiotics from wastewater treatment plants enter groundwater indirectly through surface water with high SO₄²⁻ in lightly polluted areas, while in heavily polluted areas, there are high concentrations of inorganic components in garbage leachate and wastewater leakage that carry antibiotics directly into groundwater. In summarized, the relationship between antibiotics and hydrochemistry observed in this study shows that a previous sound geochemical study may provide evidence of the extend of antibiotic occurrence.