A growing body of scientific evidence reveals that primary producers—including plants and phytoplankton—possess a previously overlooked ability to internally break down and detoxify methylmercury, one of the most potent neurotoxins circulating through global food webs. This newly identified in vivo demethylation pathway rapidly converts methylmercury into less toxic inorganic mercury, which is subsequently reduced to gaseous Hg⁰ and released back into the atmosphere. The discovery fills a critical knowledge gap that helps explain why sharp declines in mercury emissions do not translate proportionally into reduced methylmercury exposure in humans. By limiting methylmercury entry at the earliest stage of food chains, this natural process offers new possibilities for safeguarding food safety, ecosystem health, and global mercury-mitigation strategies.
Mercury pollution remains a persistent global health and environmental threat, with methylmercury posing exceptionally high risks due to its extreme biomagnification in food webs. Although the Minamata Convention on Mercury has successfully curbed anthropogenic mercury emissions, major uncertainties remain regarding how emission reductions ultimately affect methylmercury levels in our food and thus dietary exposure. Traditional understandings focus on photochemical and microbial degradation occurring in soils, sediments, and surface waters before methylmercury enters food chains. Yet persistent discrepancies between atmospheric mercury trends and biological methylmercury burdens imply the presence of unaccounted transformation processes that decouple mercury emission and methylmercury exposure. Due to these unresolved issues, a deeper investigation into biological methylmercury transformations is urgently needed.
A joint research team from Nanjing University and other collaborating institutes published (DOI: 10.1016/j.eehl.2025.100199) a Perspective article on November 7, 2025, in Eco-Environment & Health , presenting compelling evidence for a previously unrecognized biological pathway that demethylates and detoxifies methylmercury within terrestrial plants and phytoplankton. Synthesizing recent experiments across multiple species, the authors highlight how these organisms rapidly degrade methylmercury and release much of the resulting gaseous Hg⁰ into the atmosphere. Their assessment challenges long-held assumptions about mercury cycling and offers a new foundation for evaluating and advancing global mitigation efforts.
The Perspective draws on recent studies demonstrating that eight plant species and several phytoplankton taxa exhibit unexpectedly strong methylmercury demethylation capacity. Instead of serving merely as methylmercury accumulators, these organisms internally convert up to 86% of absorbed methylmercury into inorganic mercury and further reduce it to gaseous Hg⁰ within just a few days. Central to this transformation is a previously overlooked, light-independent reaction triggered by intracellular singlet oxygen, a common reactive oxygen species that attacks the elongated carbon–mercury bond in methylmercury–thiol complexes. This degradation proceeds as rapidly as, or even faster than, well-established photolytic and microbial pathways.
Because primary producers account for most of Earth's biomass, their collective demethylation activity likely contributes substantially to the atmospheric Hg⁰ pool. The authors argue that excluding this biological "pump" from mercury-cycling models creates major uncertainties in predicting methylmercury transfer into food webs and in assessing the effectiveness of global mercury-mitigation policies. The newly identified pathway provides a mechanistic explanation for why reductions in mercury emissions often result in only modest declines in methylmercury exposure in humans and wildlife.
The authors emphasize that recognizing this hidden demethylation pathway is essential for accurately assessing global mercury control strategies. They note that primary producer-mediated methylmercury degradation occurring before trophic transfer can markedly influence methylmercury levels in crops, aquatic organisms, and ultimately human diets. According to the research team, future monitoring and modeling frameworks must incorporate organism-level transformations to avoid misinterpreting environmental trends or underestimating natural detoxification. Such refined understanding, they argue, is critical to achieving meaningful protection of food safety, wildlife health, and public well-being.
This newly uncovered biological pathway opens promising avenues for sustainable mercury management. Enhancing reactive oxygen species-mediated demethylation in crops could reduce methylmercury levels in key foods such as rice, while nature-based approaches using phytoplankton or aquatic plants may support remediation of contaminated waters. The authors call for integrating emission-reduction efforts with targeted demethylation enhancement across agricultural production, food processing, and ecosystem management. Incorporating this pathway into global mercury-cycling models will enable more accurate predictions of human exposure and environmental risk, ultimately advancing progress toward food security, healthier ecosystems, and sustainable development goals.
