Comprehensive Investigation of the Transport of Di(2-Ethylhexyl) Phthalate (Dehp) in the Vadose Zone of a Typical Shale Gas Exploitation Area in Chongqing, China

Abstract

Phthalate acied esters (PAEs), particularly Di(2-ethylhexyl) phthalate (DEHP), have been identified as process-specific contaminants in shale gas extraction, yet their migration dynamics in heterogeneous vadose zones remains poorly quantified. In this study, we investigated the migration of DEHP in soils from a typical shale gas exploitation area combining soil column experiments and MIM model. The findings reveal that DEHP is the prior pollutants linking to shale gas exploitation activity, and DEHP exhibits accelerated transport in deeper soil layers, driven by reduced organic matter content and increased ionic strength. Furthermore, elevated ionic strength and higher flow rates reduced DEHP retention by 72.6-85.6%, enhancing mobility via electrostatic shielding and competitive adsorption. Model simulations suggested DEHP accumulation at the vadose zone’s bottom exceeding agricultural soil safety thresholds. Groundwater simulations further indicated that under sustained leakage scenarios, DEHP can reach concentrations in groundwater that exceed regulatory limits, even at distances of up to 100 m from the spill source. Further modeling indicated that reducing the source concentration to 1.25 mg/kg is critical to preventing significant groundwater pollution. This work reveals the non-equilibrium transport of DEHP and filling a pivotal gap in predicting PAEs fate and providing actionable metrics for shale gas environmental management.

Keywords: DEHP, Vadose zone, Shale gas exploitation, Mobile-immobile model