Biochar and iron minerals facilitate the reduction of pollution and sequestration of carbon in chloramphenicol-contaminated soil under dry conditions

Addressing chloramphenicol (CAP) contamination and enhancing soil organic carbon (SOC) sequestration are vital for environmental sustainability. This research explored the combined influence of biochar (BC), iron mineral (Fe₂O₃), and their composite (FeBC) on CAP degradation and SOC distribution across various moisture regimes, including dry, wet, and dry-wet alternation (DWA) conditions. DWA conditions were the most effective at reducing bioavailable CAP residues. However, FeBC exhibited superior CAP removal efficiency over individual BC or Fe₂O₃ treatments, with the greatest reduction observed under dry conditions. Compared with those of the control without additives, reduction rates reached 46.98 % (DRY), 14.95 % (WET), and 23.81 % (DWA), respectively. BC primarily increased particulate organic carbon (POC) content, with a notable increase of 23 % under dry conditions. In contrast, Fe₂O₃ markedly increased mineral-associated organic carbon (MAOC) content by 62 %, with the strongest effect observed under dry conditions. However, no synergistic interaction between BC and Fe₂O₃ was detected in promoting carbon sequestration. Redundancy analysis indicated a negative correlation between soil moisture and both POC and MAOC, whereas BC and Fe₂O₃ showed positive correlations with POC and MAOC, respectively. Additionally, soil moisture, BC, and Fe₂O₃ influenced soil physicochemical properties and enzyme activities, which were closely associated with CAP removal and carbon sequestration processes. The transformation of bioavailable CAP was correlated with SOC forms: enhanced POC by BC and enhanced MAOC by Fe₂O₃ facilitated the fixation of CAP. This study provides theoretical support for the development of integrated “pollution control and carbon sequestration” technologies in soils.