Distribution, accumulation pattern and driving factors of mercury in the actual field calcareous soil–wheat system of an arid industrial oasis, Northwest China
摘要
Mercury (Hg) contamination in calcareous agricultural soils poses significant risks to crop safety, yet the coupled biogeochemical interactions between Hg and essential metallic elements during plant uptake remain poorly understood. This study investigated the distribution, accumulation, and driving factors of Hg in soil–wheat systems across two contrasting watersheds in a typical industrial oasis of Northwest China. Soil Hg accumulation was strongly driven by organic matter and negatively correlated with pH and CaCO3 Vertical profiles in contaminated soils displayed a distinct subsurface peak (1.679 mg/kg at 10–20 cm) indicative of anthropogenic deposition. Wheat leaves accumulated the highest Hg concentrations and contributed 41.4–45.3% of total plant Hg, substantiating atmospheric foliar uptake as a dominant pathway. Grain Hg exceeded the food safety limit in 75% of samples from the contaminated area. Soil physicochemical properties were the dominant drivers of root and leaf bioconcentration factors, with soil Hg identified as the most important single predictor. Critically, nonlinear analyses revealed a strong competitive antagonism between Zn and Hg, where increasing leaf and root Zn dramatically suppressed root Hg bioconcentration, whereas Cu exhibited synergistic effects. These results demonstrate that Hg accumulation in wheat is a multifactorial process regulated by soil organic matter, pH, and specific metal–metal interactions. The observed altitude effect is primarily attributable to proximity to upstream industrial and mining pollution sources and to the intensity of wastewater irrigation, rather than to topographic elevation itself. This relationship is further modulated by soil pH, which acts as a key environmental constraint. These findings provide new insights into the complex soil–plant dynamics governing Hg uptake and transport, thereby establishing a scientific basis for risk assessment and food safety management in contaminated agricultural regions.
HighlightsIndustrial wastewater irrigation of soil leads to more Hg pollution. The leaves and roots of wheat are the main organs for Hg accumulation. The pH value and CaCO3 content are negatively correlated with Hg. High grain Hg accumulation is restricted to high elevations at low/neutral soil pH.