Integrated geochemical and geophysical assessment for monitoring soil stabilization with waste oyster shells

We assessed the field-scale stabilization efficiency of lead (Pb) and copper (Cu) in contaminated soils using powdered (WOS-P) and granular (WOS-G) waste oyster shell (WOS) amendments. A 9-month monitoring was conducted using geochemical leaching tests Toxicity Characteristic Leaching Procedure (TCLP), Mehlich-3, and Diethylenetriaminepentaacetic acid (DTPA) besides sequential extraction and geophysical methods. WOS-treated soils exhibited significant reductions in leaching ratios, with WOS-P showing greater efficacy. Pb and Cu leaching ratios decreased by up to 1.21 and 2.00% points, respectively. Fractional analysis confirmed the redistribution of Pb into carbonate-bound forms, with the F2 fraction increasing from 6.46 to 12.89%, and Cu into Fe-Mn oxide-bound forms (F3), which increased from 11.29 to 15.88%. Electrical resistivity (ER) and induced polarization (IP) surveys visualized the spatial evolution of stabilization. In WOS-P plots, lower ER and elevated IP responses were initially observed, consistent with those of increased ionic strength. Over time, signal attenuation suggested precipitation and geochemical fixation. WOS-G plots showed delayed IP enhancement, reflecting slower dissolution and ion release. Our results suggest that WOS can serve as an effective and sustainable stabilizer, and that combined ER and IP with geochemical monitoring offers valuable complementary insights. Future work should expand the spatial and temporal scope to validate these findings and advance integrated interpretation frameworks for more robust field applicability and quantitative stabilization assessment.