A bioreporter-toxicity-characteristic-leaching-procedure (Bio-TCLP) test battery approach for risk assessment and...

Hexavalent chromium [Cr(VI)] is a highly toxic metal, and its extensive use in industry has led to widespread soil contamination. Biochar is a cost-effective and practical amendment for Cr stabilisation, with remediation performance typically assessed using conventional chemical methods such as the toxicity characteristic leaching procedure (TCLP). However, reliance solely on chemical concentration data may be inadequate for comprehensive risk assessment. There is a growing need for integrated approaches that combine chemical and toxicological evaluations. In this study, we developed a novel test battery approach, termed Bio-TCLP, by coupling whole-cell bioreporter assays with the TCLP to concurrently evaluate Cr leaching potential and associated toxicity. Although remediation using nanoscale zerovalent iron (nZVI) and biochar effectively reduced Cr(VI) levels as determined by TCLP, the Bio-TCLP results revealed residual leachate toxicity, primarily attributed to reactive oxygen species (ROS). To enhance the efficacy of remediation, an Eucalyptus-derived biochar functionalised with nZVI (EBC-nZVI) was synthesised. This composite achieved over 80% Cr(VI) reduction and, importantly, EBC-NZVI significantly reduced measurable ecotoxicity to below detection limits in the Bio-TCLP assay. This study introduces and validates the Bio-TCLP test battery approach as a dual-function tool for evaluating both the chemical and biological dimensions of remediation performance, supporting more robust risk assessment frameworks for contaminated site management.