Staple crops as a key hub of biogeochemical mercury cycle across China.

Abstract

Mercury (Hg) contamination threatens human health and ecological security. Plants play a critical role in regulating the global Hg cycle, yet how agricultural crops influence Hg transport remains elusive. Here we show that staple crops (i.e., wheat, rice, and maize) assimilate 25.59 Mg Hg annually using a standardized field survey of 301 sites across China, with approximately 53% originating from the atmosphere and 47% from the soil based on Δ¹⁹⁹Hg signatures. We further predict the North China Plain, Jiangnan Hills, and Northeast Plain as hotspots of crop Hg accumulation in China. Following harvest, 36.4% of the Hg accumulated by staple crops is returned to the soil as residues, while 43.4% is transferred to the food chain via grain consumption and straw-livestock feed. These findings demonstrate that staple crops act as a key hub in global Hg cycling, with implications for assessing the fate and risk of existing Hg on Earth.