Periodic Reporting for period 2 - SPONGE (Surface runoff as source of microplastics and emerging contaminants in megacities aquifers)
Période du rapport: 2024-11-11 au 2025-11-10
Urban areas are increasingly affected by groundwater contamination due to rapid urbanisation, ageing infrastructure, and the accumulation of emerging pollutants. Among these, microplastics (MPs) and pharmaceutical compounds, such as antibiotics, have raised growing concern because of their persistence in the environment and their potential impacts on ecosystems and human health. While surface waters have been extensively investigated, urban groundwater systems remain poorly studied, despite they can be a critical source of drinking water for a large portion of the global population.
This lack of knowledge is particularly relevant in the context of nature-based solutions, such as the sponge city concept, which promotes stormwater infiltration to enhance urban water resilience. Understanding whether stormwater and other non-conventional water sources can safely contribute to groundwater recharge without degrading water quality is therefore a key societal and environmental challenge.
The SPONGE project was designed to address this gap by investigating the occurrence, transport, and fate of microplastics and emerging contaminants in urban groundwater systems, using the rapidly urbanising megacity of Shenzhen (Guangdong, China) as a case study. The overall objective of the project was to assess the suitability of urban stormwater and other non-conventional recharge sources for groundwater recharge, with a specific focus on microplastics and antibiotics, while improving the understanding of contamination pathways and controlling processes in urban aquifers.
As a final outcome, the project concludes that urban groundwater systems cannot be assumed to be naturally protected from emerging contaminants and that site-specific hydrogeological conditions play a fundamental role in controlling contamination risks.
This lack of knowledge is particularly relevant in the context of nature-based solutions, such as the sponge city concept, which promotes stormwater infiltration to enhance urban water resilience. Understanding whether stormwater and other non-conventional water sources can safely contribute to groundwater recharge without degrading water quality is therefore a key societal and environmental challenge.
The SPONGE project was designed to address this gap by investigating the occurrence, transport, and fate of microplastics and emerging contaminants in urban groundwater systems, using the rapidly urbanising megacity of Shenzhen (Guangdong, China) as a case study. The overall objective of the project was to assess the suitability of urban stormwater and other non-conventional recharge sources for groundwater recharge, with a specific focus on microplastics and antibiotics, while improving the understanding of contamination pathways and controlling processes in urban aquifers.
As a final outcome, the project concludes that urban groundwater systems cannot be assumed to be naturally protected from emerging contaminants and that site-specific hydrogeological conditions play a fundamental role in controlling contamination risks.
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.
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.
SPONGE significantly advanced the state of the art by demonstrating that urban groundwater cannot be considered naturally protected from microplastic and pharmaceutical contamination. The project moved beyond descriptive studies by integrating innovative analytical techniques, such as Atomic Force Microscopy (AFM) for micro- and nanoplastic detection, and pore-scale numerical modelling to simulate microplastic transport in porous media.
These modelling approaches showed that grain size, pore throat dimensions, and hydraulic gradients strongly control particle retention and transport, providing mechanistic insights that go beyond traditional laboratory infiltration experiments. The project also highlighted the importance of non-conventional recharge sources, such as sewer leakage and irrigation of urban green areas, in controlling groundwater quantity and quality.
From a socio-economic and societal perspective, SPONGE contributes to a better understanding of the risks associated with groundwater use in urban environments, supporting more informed water management and urban planning strategies. The results underline the need for site-specific, hydrogeology-based approaches, rather than generic solutions, when designing nature-based recharge systems such as sponge cities.
Overall, the project provides scientific evidence and methodological tools that can support policymakers, water managers, and researchers in developing safer and more sustainable urban groundwater management strategies.
on in subsurface environments, and is expected to have long-term influence on both science and society.
These modelling approaches showed that grain size, pore throat dimensions, and hydraulic gradients strongly control particle retention and transport, providing mechanistic insights that go beyond traditional laboratory infiltration experiments. The project also highlighted the importance of non-conventional recharge sources, such as sewer leakage and irrigation of urban green areas, in controlling groundwater quantity and quality.
From a socio-economic and societal perspective, SPONGE contributes to a better understanding of the risks associated with groundwater use in urban environments, supporting more informed water management and urban planning strategies. The results underline the need for site-specific, hydrogeology-based approaches, rather than generic solutions, when designing nature-based recharge systems such as sponge cities.
Overall, the project provides scientific evidence and methodological tools that can support policymakers, water managers, and researchers in developing safer and more sustainable urban groundwater management strategies.
on in subsurface environments, and is expected to have long-term influence on both science and society.