Bio-electrochemical interface behaviours at kaolinite-toluene-water systems: Implications for contaminant monitoring in clayey soils

This study investigated the relationship between toluene concentration and a detection tool driven by pH and oxidation-reduction potential (ORP) in representative samples and elucidated its applicability to pollutant monitoring in clayey soils by firstly analysing the bio-electrochemical interface behaviours at kaolinite-toluene-water systems. The results show that the ORP/pH indicator exhibited a strong nonlinear correlation (coefficient of determination R 2 = 0.925 (adjusted value)) and a low testing error (3.52%), and its value changed correspondingly in the presence and variation of toluene. Consequently, it is feasible to utilise an ORP/pH-based detection tool to reflect toluene concentrations (0.1–30 wt%) in kaolin systems, which also showed good fitting ( R 2 = 0.908) and thermal applicability (23 °C–60 °C; R 2 = 0.874). The core mechanisms associated with the toluene concentrations and ORP/pH values in the kaolinite-toluene-water system are that toluene can: (i) mask kaolinite surface sites, influence the thickness of the electrical double layer, and subsequently alter the exchange and transfer of cations and electrons within kaolinite; this can be revealed by the changes in leached Al ion, Si ion, and zeta potential (all of which have a good linear fitting relationship with ORP/pH values) and (ii) impact and shift the species composition, abundance, and total biomass of microorganisms at the kaolin interface, where the observed hormesis effect at low contamination level (0.1 wt%) and 90% biomass reduction at 10 wt% contamination level suggest dual roles of microorganisms in electron transfer processes. • ORP/pH-based tool can reflect toluene concentrations (0.1–30 wt%) in kaolin system • The tool has thermal applicability within 23–60°C to monitor toluene ( R 2 = 0.874) • Toluene alters the bio-electrochemical behaviours at interfaces to affect ORP and pH • Toluene can impact EDL thickness and surface charge transfer of kaolinite • Toluene affects microbial-induced bio-electrochemical behaviours at interfaces