{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,15]],"date-time":"2026-09-15T11:03:49Z","timestamp":1789470229971,"version":"build-2803163510"},"reference-count":33,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,5]],"date-time":"2026-09-05T00:00:00Z","timestamp":1788566400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Fundamental Research Funds for the Central Public-interest Scientific Institution","award":["2024YSKY-05"],"award-info":[{"award-number":["2024YSKY-05"]}]},{"DOI":"10.13039\/501100011316","name":"Open Research Fund of Key Laboratory of Eco-industry of Ministry of Ecology and Environment, Chinese Research Academy of Environmental Sciences","doi-asserted-by":"publisher","award":["2024KFF-04"],"award-info":[{"award-number":["2024KFF-04"]}],"id":[{"id":"10.13039\/501100011316","id-type":"DOI","asserted-by":"publisher"}]},{"award":["2024KFF-04"],"award-info":[{"award-number":["2024KFF-04"]}],"id":[{"id":"https:\/\/ror.org\/05t8xvx87","id-type":"ROR","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100004829","name":"Sichuan Science and Technology Program","doi-asserted-by":"publisher","award":["2026NSFSC0270"],"award-info":[{"award-number":["2026NSFSC0270"]}],"id":[{"id":"10.13039\/501100004829","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Toxics"],"abstract":"<jats:p>Biochar has been widely applied for immobilization of potentially toxic elements (PTEs) in contaminated soils; however, its effects on metal transport under transient unsaturated conditions remain insufficiently understood. This study investigated the adsorption, desorption, and transport behavior of Pb2+ and Cd2+ in biochar-amended soils by combining batch experiments, unsaturated conditions column experiments, and transport modeling. The adsorption kinetics, isotherms, and desorption characteristics of Pb2+ and Cd2+ were evaluated under different biochar levels, and their redistribution during unsaturated infiltration was further analyzed using soil\u2013water-dependent models. Biochar increased the apparent adsorption capacity of both metals, with a stronger response observed for Pb2+ than Cd2+. The Elovich and two-constant models provided better statistical descriptions of adsorption kinetics than the pseudo-second-order model, indicating that adsorption rate behavior involved heterogeneous and multi-rate processes. Freundlich fitting showed that Pb2+ and Cd2+ exhibited non-ideal adsorption behavior, while desorption experiments demonstrated a stronger reduction in apparent Pb2+ release compared with Cd2+ under biochar. Under transient unsaturated infiltration, Pb2+ and Cd2+ exhibited distinct transport patterns. Pb2+ redistribution was adequately described by a linear partitioning relationship, with R2 values ranging from 0.988 to 0.990, indicating relatively stable solid\u2013liquid partitioning within the tested conditions. In contrast, Cd2+ showed stronger dependence on soil\u2013water conditions, and an empirical nonlinear water-dependent model improved model performance, increasing R2 values from 0.533\u20130.652 for the linear model to 0.903\u20130.973. The results suggest that biochar effects on potentially toxic element migration under unsaturated conditions are element-specific, involving both apparent sorption enhancement and water-dependent redistribution processes. This study highlights that biochar performance in potentially toxic elements remediation should not be evaluated solely based on equilibrium adsorption capacity. Under field-relevant unsaturated conditions, amendment effectiveness may also depend on interactions between metal-specific retention behavior and soil hydraulic variability. Further studies integrating structural characterization, long-term aging, and reactive transport modeling are required to validate these processes under heterogeneous field conditions.<\/jats:p>","DOI":"10.3390\/toxics14090787","type":"journal-article","created":{"date-parts":[[2026,9,7]],"date-time":"2026-09-07T12:12:25Z","timestamp":1788783145000},"page":"787","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Biochar Regulates Contrasting Pb2+ and Cd2+ Transport Regimes Through Water-Dependent Partitioning Transitions Under Unsaturated Conditions"],"prefix":"10.3390","volume":"14","author":[{"given":"Xin","family":"Tan","sequence":"first","affiliation":[{"name":"Key Laboratory of Eco-Industry of Ministry of Ecology and Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China"},{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"given":"Yilan","family":"Li","sequence":"additional","affiliation":[{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Lina","family":"Xu","sequence":"additional","affiliation":[{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"given":"Jing","family":"Tian","sequence":"additional","affiliation":[{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"investigation","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"}]},{"given":"Jiaqi","family":"Tan","sequence":"additional","affiliation":[{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Jiuli","family":"Ruan","sequence":"additional","affiliation":[{"name":"Key Laboratory of Eco-Industry of Ministry of Ecology and Environment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"validation","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1194-3341","authenticated-orcid":false,"given":"Yang","family":"He","sequence":"additional","affiliation":[{"name":"School of Environmental Science and Engineering, Southwest Jiaotong University, Chengdu 611756, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"conceptualization","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1054","DOI":"10.1016\/j.scitotenv.2016.05.115","article-title":"Maps of heavy metals in the soils of the European Union and proposed priority areas for detailed assessment","volume":"565","author":"Hermann","year":"2016","journal-title":"Sci. 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