Municipal sludge disposal emerges as a major, hidden, and rapidly growing atmospheric mercury source

Wastewater treatment greatly reduces mercury pollution in aquatic ecosystems but does not eliminate it. Here, we identify municipal sludge disposal as a major, long-overlooked atmospheric mercury source. In China, sludge disposal emitted 42 - 10 + 18 Mg in 2024, exceeding 10% of national anthropogenic emissions and ranking third after cement production and nonferrous metal smelting. These emissions have increased by nearly a thousandfold since the 1970s and are concentrated in densely populated urban areas, driven by the rapid expansion of sludge incineration, codisposal, and composting. Our findings reveal a cross-media pollution transfer embedded in sustainability transitions and call for sludge disposal to be incorporated into UNEP mercury budget and Minamata Convention assessments.