Impact of pharmaceutical (diclofenac) contamination on the compressibility and strength of residual soil: Towards a resilient urban infrastructure

Increased access to pharmaceuticals necessitates proper disposal practices to prevent environmental contamination. Irresponsible disposal leads to the infiltration of pharmaceuticals, which can potentially affect the soil's engineering and agricultural properties. Literature focusing on this topic is limited, which is the motivation of this study. The main aim of this study is to assess the impact of increasing concentrations of pharmaceutical (diclofenac) in pore water on the compressibility and strength characteristics of Malaysian residual soil and potential implications affecting the safety and stability of urban infrastructure. This aim is achieved using a series of standard laboratory experiments to determine one-dimensional (1D) consolidation, direct shear strength, stress-dilatancy, and critical-state behaviors of compacted residual clay samples. The experiments also examined the compressibility and volume change behaviors of normally consolidated soil samples (consolidated at four different initial consolidation pressures) upon sudden infusion of diclofenac solution under time-controlled infusion. The results show that the diclofenac solution significantly influences the response of the residual soil samples, including volume change, strength, and dilatancy behaviors. However, the extent of this influence depends on factors such as the drug matrix, concentration, and type of cations, clay mineralogy, and the significance of the diffused double layer surrounding the clay particles. Further studies employing a more comprehensive range of drugs, soil types, and real-world contamination scenarios (a combination of multiple contaminants) are recommended. The outcomes from this study can inform policy decision-makers on waste disposal regulations (UN-SDG 12) and help develop new or revised long-term design limits to address pharmaceutical intrusion (UN-SDG 11).