Heavy metal contamination and remediation in deep drilling across Chinese energy basins.

Deep and ultra-deep drilling in China's energy basins generates drilling fluids, cuttings, and produced water that can mobilize potentially toxic elements into soils, sediments, and aquifers. This review summarizes evidence from the Xinjiang Tarim Basin, Sichuan Basin, and Bohai Bay region on contaminant sources, release and transport pathways, ecological and human exposure, and management options. Cadmium (Cd), arsenic (As), lead (Pb), chromium (Cr), nickel (Ni), vanadium (V), (zinc) Zn, and Barium (Ba) are commonly reported in drilling-related wastes and affected media, but mobility depends on speciation, pH, redox conditions, soil properties, and hydrogeology. Prevention through lower-toxicity drilling fluids, closed-loop waste handling, well integrity, and source containment should be prioritized. Stabilization, soil washing, membrane and electrochemical treatment, phytoremediation, and bioremediation require site-specific selection. Standardized monitoring, speciation data, field validation, and direct links between engineering controls and risk reduction are needed to support safer drilling and evidence-based regulation.