Impact of pharmaceutical waste (diclofenac) on consistency and particle packing of a Malaysian urban residual clay

Rising demand for pharmaceuticals has raised concerns about their production and disposal, as poor management can harm the environment. Pharmaceutical waste, including unused and expired medications, mainly comes from households, the pharmaceutical industry, and healthcare facilities. These contaminants can enter the environment through soil, wastewater, landfill leachate, and agricultural runoff and alter the consistency of natural soil. However, limited literature on this topic was encountered during our review, which motivated this study. This research investigates the effect of diclofenac on the consistency and particle packing of Malaysian residual clay using laboratory experiments. Diclofenac was chosen because of its widespread use and frequent detection in the environment. Standard laboratory tests, including consistency limit, mini-compaction, and vane shear tests were performed using varying concentrations of diclofenac and molding water contents. Liquid limit decreased by 5 %, and plastic limit dropped by 26.8 % in samples with 10 g/L diclofenac concentration. While mini-compaction tests showed a 5 % increase in dry unit weight (17.0 to 17.8 kN/m³) and a 14 % decrease in optimum water content. These are related to changes in diffused double layer from flocculation, affecting particle interactions and soil consistency. Vane shear tests indicated that diclofenac does not significantly impact the shear strength of residual soil. This study highlights the influence of pharmaceutical-derived cations on soil consistency and packing, which may vary by tablet matrix and cations released. These findings emphasize for further research considering different pharmaceuticals and soil types to enhance pharmaceutical waste disposal (United Nations Sustainable Development Goal-12).