From Surface Water to Deep Groundwater: Field Evidence of Fate and Transport of Pharmaceuticals and Personal Care Products (PPCPs) in Urban Alluvial Systems of Delhi, India

Pharmaceuticals and personal care products (PPCPs) from wastewater discharge are increasingly detected in urban river systems; however, their subsurface fate and transport remain poorly understood at the field scale. Here, we investigate the vertical migration and subsurface distribution of emerging organic contaminants (EOCs) at three anthropogenically impacted sites in the Yamuna River basin, Delhi, India: the Yamuna Riverbank, a major urban drain that discharges directly into the river, and an artificial lake that receives treated wastewater effluent. Target compounds included antibiotics, endocrine-disrupting compounds, prescription and over-the-counter pharmaceuticals, sewage-associated tracers, and an artificial sweetener.

Soil samples spanning the vadose and saturated zones were collected down to 30 m below ground level using standard penetration testing and the bailer (“Boki”) method. Nested piezometers enabled the spatiotemporal monitoring of surface water and groundwater in shallow, intermediate, and deep layers over a one-year period.

Deep penetration of PPCPs was observed at all three sites, with at least ten target compounds quantified in both soils and groundwater down to a depth of 30 m. Estrone exhibited the highest concentrations in soils, while non-steroidal anti-inflammatory drugs were the most frequently detected compound class across sites. Seven compounds showed detection frequencies exceeding 90% in soils at all three sites. Multivariate statistical analyses linked compound-specific distribution patterns to soil chemistry and subsurface hydrogeology. Stable isotope analysis (δ¹⁸O, δ²H) and fluorescence dissolved organic matter (fDOM) characterisation were applied to elucidate surface water–groundwater interactions. Soil mineralogy and elemental composition were characterised using X-ray diffraction (XRD) and X-ray fluorescence (XRF) to assess geochemical controls on contaminant retention and mobility.

In addition to targeted monitoring of 27 compounds, suspect and non-target screening was conducted on surface and groundwater samples to identify transformation products and to assess the influence of redox and geochemical conditions on subsurface transformation processes. Laboratory-scale batch sorption and biodegradation experiments conducted at environmentally relevant concentrations were used to support the interpretation of field-scale observations.

These results demonstrate that PPCPs can migrate vertically through soils and persist across both the vadose and saturated zones, with significant implications for groundwater quality, particularly in regions where rivers serve as both wastewater receivers and aquifer recharge zones.