Declines in Riverine Mercury Export from China Driven by Water Pollution Controls

Area of Science:

• Environmental Chemistry
• Geochemistry
• Ecotoxicology

Background:

• Recent pollution controls in China aimed to reduce mercury (Hg) release.
• The impact of these controls on riverine Hg export was previously unknown.

Purpose of the Study:

• To assess the effects of pollution controls on riverine Hg export in China.
• To identify sources and trends of national riverine Hg export.
• To evaluate the contribution of riverine Hg export to East Asian sediment Hg.

Main Methods:

• Measured Hg concentrations and isotopic compositions in 12 major Chinese rivers (2021-2022).
• Utilized Hg isotope mixing models to determine Hg sources.
• Combined source identification with atmospheric Hg observations.

Main Results:

• Total Hg (THg) levels decreased two- to twentyfold compared to previous observations.
• Riverine THg export was estimated at 45.1 ± 12.1 Mg yr⁻¹, a 46% decrease from 2016.
• Water pollution controls accounted for ~95% of the decline in riverine THg export.
• Riverine export contributes significantly to estuarine (~67%) and continental shelf (~45%) sediment Hg in East Asia.

Conclusions:

• Water pollution controls in China have substantially reduced riverine Hg export.
• These controls offer co-benefits for mitigating Hg pollution and associated risks in coastal ecosystems.
• Riverine Hg export remains a key pathway for Hg transfer to marine environments.