SPONGE combined field monitoring, laboratory analyses, and numerical modelling. A comprehensive monitoring network was established, including groundwater wells, springs, stormwater drains, and wastewater systems. Multiple sampling campaigns were conducted during both dry and wet seasons to capture seasonal variability.
Water samples were analysed for microplastics, antibiotics, pharmaceutical compounds, major ions, trace elements, and isotopic tracers of water (²H, ¹⁸O) and nitrate (¹⁵N, ¹⁸O). This integrated, multi-tracer approach provided a comprehensive understanding of urban groundwater processes that cannot be achieved using a single analytical technique. Results highlighted the presence of multiple recharge sources, both conventional and non-conventional, affecting the aquifer and leading to complex recharge dynamics and multiple contamination pathways.
One of the main scientific results of the project is the demonstration that urban groundwater in Shenzhen is already contaminated by microplastics, even when considering only particles larger than 20 µm. MP concentrations showed spatial and seasonal variability, with generally higher values during the rainy season, indicating the key role of hydrodynamic processes in particle mobilisation. Stormwater and wastewater exhibited significantly higher MP concentrations than groundwater; however, their strong variability prevented the identification of a single dominant source.
The project also revealed widespread contamination by antibiotics and pharmaceutical compounds, especially in groundwater wells located in older urbanised areas. Unlike microplastics, antibiotic concentrations did not show a clear seasonal pattern, indicating that continuous leakage from sewer networks represents a major and persistent contamination source. Nitrate isotope analyses further confirmed the strong influence of wastewater inputs and highlighted the highly reactive and seasonally controlled behaviour of the shallow urban aquifer.
Results were exploited through peer-reviewed open-access publications, presentations at international conferences, workshops, and knowledge transfer activities, ensuring wide dissemination within the scientific community and beyond.
