Rapid on-site determination of heavy metals and metalloids in contaminated biochar samples by accelerated leaching process coupled with voltammetric sensors

Heavy metals and metalloids are the most common environmental pollutants. Toxicity characteristic leaching procedure (TCLP) is a standard operating procedure that is used to assess heavy metal and metalloid compositions, and evaluate the hazardous nature of waste and waste-derived materials for reuse or disposal, such as determining landfill suitability. However, TCLP and the following detections are time-consuming and require bulky laboratory-based instruments and trained personnel. To address these limitations, this study introduced a custom-made portable leaching device utilizing ultrasonics to accelerate heavy metal and metalloid leaching from solid samples, with contaminated biochar selected as a model material. The newly established leaching protocol was closely correlated with TCLP results while reducing leaching time from 18 h to 30 min. Following the leaching of heavy metals and metalloids, voltammetric methods were established for the simultaneous detection of As(III and total), Cd(II), Cr(III and VI), Pb(II), Pd(II), and Hg(II), completing the analysis within 15 min. The entire process, mainly including leaching and analysis, was completed within 1 h, with the overall performance meeting the local landfill acceptance criteria of the TCLP protocol. This study provided an innovative, rapid on-site integrated platform for heavy metal and metalloid determination in waste materials. The proposed analytical method was validated against standard techniques, including inductively coupled plasma optical emission spectroscopy (ICP-OES) and high-performance liquid chromatography coupled with triple quadrupole inductively coupled plasma mass spectrometry (HPLC-ICP-QQQ), demonstrating its reliability and effectiveness.