New study reveals underestimated pathway for arsenic pollution in water

Biochar Editorial Office, Shenyang Agricultural University

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Unveiling an overlooked pathway of water arsenic contamination: microscale evidence of enhanced arsenic mobility from the rhizosphere to detritusphere of macrophytes

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Credit: Cai Li, Xin Ma, Xue Jiang, Youzi Gong, Xiaolong Wang, Musong Chen, Qin Sun, & Shiming Ding

A team of scientists has uncovered a hidden risk to freshwater quality that could affect millions worldwide: the shift of lake and river sediment from trapping toxic arsenic to releasing it, driven by the widespread loss of aquatic plants. Their research, recently published in Energy Environment Nexus, shows that the decline of submerged macrophytes, vital underwater plants, can fundamentally change how arsenic moves through aquatic environments, posing an unanticipated threat to water safety.

From Pollution Shield to Pollution Source

For decades, submerged macrophytes like Vallisneria natans have played a quiet protective role in many freshwater ecosystems. Their roots actively release oxygen into the sediment, which encourages beneficial chemical reactions and microbial activity. This causes arsenic, a notorious toxin linked to cancer and other health issues, to become trapped in iron plaques that form around the roots. As a result, sediment under healthy aquatic plants acts as a sink, keeping arsenic from leaching into the water.

However, the new research has found that when these plants die, a phenomenon now accelerating worldwide due to water pollution and climate change, the situation reverses. Without living roots to provide oxygen, sediments switch from aerobic (oxygen-rich) to anaerobic (oxygen-poor) conditions. This environmental shift dissolves the iron plaques and sets arsenic free, transforming the sediment into a source of contamination that releases toxic compounds back into the water above.

“Our experiments revealed a dramatic transition,” said Dr. Cai Li, lead author of the study. “During plant growth, arsenic is effectively immobilized. But after plant death, as the roots decompose, arsenic mobility can increase several-fold, creating localized hotspots of contamination.”

High-Resolution Microscale Insights

The research team utilized advanced microscale sampling and high-throughput genetic sequencing to closely monitor arsenic, iron, and microbial activity in the sediment, both before and after plant decay. They observed that after plant death, the abundance of iron-reducing bacteria surged by over 80 percent, contributing to a nearly 90 percent loss of arsenic once bound within the root’s protective iron plaque. Genetic analysis indicated a sharp drop in bacterial genes responsible for turning the most toxic forms of arsenic into safer ones, leading to greater risk of arsenic remaining available and mobile in the environment.

These findings suggest that the decline of submerged aquatic vegetation could tip formerly stable sediments into new pollution hotspots, potentially elevating arsenic levels in water and increasing exposure risks for people, wildlife, and crops.

Implications for Lake Management and Restoration

According to the authors, submerged macrophyte coverage in global lakes has plummeted by more than 30 percent in just the past two decades. As these crucial plants vanish, their protective ecosystem functions are lost, and so is the sediment’s capacity to keep arsenic locked away.

“Most water restoration projects rightly focus on removing pollutants, but our results show that losing aquatic vegetation can trigger unexpected water quality threats,” explained co-author Dr. Shiming Ding. “Restoration strategies must address both the removal of contamination and the long-term stability of plant communities in lake and river sediments.”

The researchers recommend adding materials with oxygen-releasing or iron-stabilizing properties to sediment surfaces in lakes undergoing plant loss, to slow or prevent the release of arsenic and other hazardous elements. Their work provides a new perspective on how aquatic plant growth and decay affect pollution risks, highlighting the importance of ongoing monitoring and habitat protection.

Warning Sign for Aqueous Arsenic Pollution

The study’s authors hope their findings will help agencies, managers, and the public recognize the “double-edged sword” of aquatic plant beds: as sinks under healthy conditions, but as sources of pollution after plant loss or death. Protecting and restoring submerged macrophytes should now be seen as a critical part of any long-term water quality management plan, particularly in regions with known arsenic contamination.

 

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Journal reference: Li C, Ma X, Jiang X, Gong Y, Wang X, et al. 2025. Unveiling an overlooked pathway of water arsenic contamination: microscale evidence of enhanced arsenic mobility from the rhizosphere to detritusphere of macrophytes. Energy & Environment Nexus 1: e008     https://www.maxapress.com/article/doi/10.48130/een-0025-0003   

 

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About Energy & Environment Nexus:
Energy & Environment Nexus is an open-access journal publishing high-quality research on the interplay between energy systems and environmental sustainability, including renewable energy, carbon mitigation, and green technologies.

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DOI

10.48130/een-0025-0003 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Unveiling an overlooked pathway of water arsenic contamination: microscale evidence of enhanced arsenic mobility from the rhizosphere to detritusphere of macrophytes

 

Duckweed offers promise and caution as nature-based solution for rice paddy pollution

Biochar Editorial Office, Shenyang Agricultural University

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Mechanistic evaluation of duckweed intervention on reactive nitrogen gas fluxes from paddy soils

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Credit: Yiyu Lan, Shuhan Xu, Xiangyu Liu, Detian Li, Qingnan Chu, Dianming Wu, Yanwen Xu, Ping He, Chengrong Chen & Zhimin Sha

A new study has revealed both the promise and the complexity of using duckweed as a biological tool for managing nitrogen pollution in rice agriculture. While this tiny floating plant can sharply curb certain harmful nitrogen oxide emissions, it may also unintentionally boost releases of ammonia and a potent greenhouse gas, nitrous oxide. These findings highlight the importance of smart, integrated strategies for sustainable farming and environmental protection.

Nitrogen: Friend to Farmers, Challenge to Planet

Rice feeds nearly half the world’s population, and nitrogen fertilizers are vital for high yields. Yet much of this nitrogen escapes from paddy fields as reactive nitrogen gases, contributing to air and water pollution, soil acidification, and climate change. International research teams have long sought alternatives that can boost yield while reducing environmental damage.

Duckweed’s Surprising Dual Impact

The study, published in Nitrogen Cycling, explored the impact of duckweed (Lemna minor L.) on the release of five types of reactive nitrogen gases from flooded paddy soils. Using high-precision chambers, scientists closely monitored gases under different conditions: with only soil, with nitrogen-fertilized soil, and with both fertilizer and duckweed.

Results showed that introducing duckweed reduced cumulative emissions of harmful nitrogen oxides, specifically HONO and NOx—by over 70 percent and 50 percent, respectively, when compared to fertilized soil without duckweed. The key lies in duckweed’s ability to alter soil chemistry and encourage beneficial microbial communities that suppress nitrogen oxide production. By covering flooded soil, duckweed changes the redox conditions, raises pH, and influences how nitrogen is processed—a win for efforts to curb acid rain and lower harmful air pollution.

But this success comes with a catch. The same conditions that reduce nitrogen oxides can lead to a dramatic increase in emissions of ammonia (NH3) and nitrous oxide (N2O). In the study, duckweed tripled N2O emissions and caused a 140-fold increase in ammonia release. This is largely due to the breakdown of duckweed biomass, which adds loosely-bound carbon and nitrogen to the soil. Microbial activity then transforms these nutrients into gases that escape quickly to the atmosphere.

The Science Behind the Trade-Off

Researchers used molecular tools to pinpoint how duckweed alters gene activity in soil microbes. They found spikes in genes responsible for denitrification and ammonia production, providing a clear mechanism for the shift in gas emissions. Advanced modeling techniques showed that duckweed’s impact on each gas is the result of many direct and indirect factors, including changes in soil moisture, pH, available nutrients, and microbial gene expression.

The message is clear: nature-based interventions like duckweed can play a powerful role in pollution control, but their application must be carefully managed to avoid swapping one environmental problem for another.

Towards Smarter, Sustainable Solutions

The authors suggest combining duckweed with additional measures, such as timely harvesting and soil amendments, to capture its benefits while limiting unintended emissions. Removing duckweed biomass before it decomposes can prevent secondary pollution, and using materials like biochar or nitrification inhibitors can help manage excess nitrogen.

“Duckweed should be viewed as part of a toolkit for sustainable rice farming, not a single fix,” says Dr. Zhimin Sha, senior author of the study. “Our findings point to the need for integrated management strategies that balance multiple environmental goals.”

While conducted under controlled laboratory conditions, the research provides a crucial step toward field-ready solutions for cleaner, more efficient rice production. The team calls for long-term field studies and system-level evaluations to fully capture the real-world impact of duckweed interventions.

This work underscores the importance of looking at the whole environmental picture when designing new agricultural practices. Sometimes, the tiniest plants can have the biggest, and most nuanced, effects.

 

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Journal Reference: Lan Y, Xu S, Liu X, Li D, Chu Q, et al. 2025. Mechanistic evaluation of duckweed intervention on reactive nitrogen gas fluxes from paddy soils. Nitrogen Cycling 1: e008    

https://www.maxapress.com/article/doi/10.48130/nc-0025-0008

 

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About Nitrogen Cycling:
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.

Follow us on Facebook, X, and Bluesky. 

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DOI

10.48130/nc-0025-0008 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Mechanistic evaluation of duckweed intervention on reactive nitrogen gas fluxes from paddy soils

 

Medical evidence crucial in holding polluters accountable for harming health

Advances in attribution science are opening up new routes for climate justice; Health professionals everywhere should play their part in this process

BMJ Group

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Medical and scientific evidence is proving invaluable in holding public authorities accountable for the impact of unlawful air pollution on people’s health, say experts in The BMJ’s climate issue today.

Gaia Lisi and Rupert Stuart-Smith at the University of Oxford say that relatively few studies attributing health impacts to climate change have been published so far, but as this research field matures, methods are becoming more widely recognised, opening up new routes for climate accountability.

They describe recent cases where medical and scientific evidence has been used to defend human rights to health.

For example, in the UK, the inquest into the death of 9-year-old Ella Adoo-Kissi-Debrah concluded that exposure to high levels of air pollution contributed materially to her death, while in a case against Italy, the European Court of Human Rights used peer reviewed research to establish a “real and imminent risk” to life.

Similarly, in a series of civil liability cases in France, medical evidence was used to prove causal links between short term peaks in air pollution and aggravation of respiratory symptoms in children.

And they say scientific evidence demonstrating the human health consequences of climate change is likely to assume greater importance in lawsuits in national, regional, and international forums following recent advisory opinions on climate change by the Inter-American Court of Human Rights and International Court of Justice saying that states have specific duties to protect the health of individuals from life threatening effects of climate change.

In lawsuits concerning environmental pollution, they also point out that medical experts have had a key role in helping courts understand the protections needed to uphold health related laws, be it through conducting research underpinning legal arguments and judicial decisions, acting as expert witnesses, or providing third party evidence.

“Improved understanding of the health consequences of climate change could have a similar effect, clarifying the extent to which states are meeting their legal obligations to protect health, and opening up routes for climate justice where they fall short,” they conclude.

In a linked article, Laura Clarke at ClientEarth and Hugh Montgomery at University College London, say these landmark court decisions mean that big emitters, both states and companies, can no longer feign ignorance about the impacts of their activities.

“As attribution science strengthens further, we expect to see more class actions and damages claims brought by climate affected communities which, when they scale, will change the calculations and business models of big emitters,” they add.

They suggest that health professionals can help in characterising and appropriately attributing cause of deaths and disease resulting from the direct and indirect impacts of climate change, such as the direct health consequences of heatwaves on kidney and heart disease, or reproductive health.

However, attribution to socioeconomic impacts will require the development of new models, they note.

Medical professionals can also drive action by helping to support legal interventions where those responsible for high greenhouse gas emissions are wilfully indifferent or unresponsive, they add.

“If we are to make progress on emissions, action will require holding big polluters to account through the courts. Medical professionals, everywhere, should play their part in this process,” they conclude.

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Journal

The BMJ

DOI

10.1136/bmj.r1568 

Method of Research

Commentary/editorial

Article Title

Medical evidence drove legal action to clean up the air we breathe—climate justice may be next

COI Statement

GL is employed as a legal associate at the Climate Litigation Network, a not-for-profit foundation based in the Netherlands. RSS discloses funding from the Wellcome Trust and Quadrature Climate Foundation. HM is the (all positions unpaid) co-chair of the UK Health Alliance on Climate Change; co-chair, Lancet Countdown on Health and Climate Change; co-lead, UCL MSc on health and climate change; member of the sustainability advisory board at Chiesi Pharmaceuticals; and sustainability co-lead for the UK Intensive Care Society. HM iscofounder of the charity funded non-profit organisation Real Zero, which tries to drive action on climate change by leveraging the healthcare economy. LC is trustee, Lancet Countdown on Health and Climate Change.

 

Tie climate action to protecting a way of life to increase motivation, study says

Study of participants from six countries including UK and USA finds reducing psychological distance from impacts of climate change strongest driver of increased effort

University of Birmingham

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People need to feel that climate change is affecting them now or that taking action is a patriotic act for their country to overcome apathy towards environmental efforts, a new global study has found.

 

In a paper published in Communications Psychology today, a global team of researchers led by the University of Birmingham have found that motivational interventions to successfully make climate action more important to people include showing how climate change is happening now and affecting them or others like them.

 

The research team worked with participants from six countries around the world: the UK, USA, Bulgaria, Greece, Sweden and Nigeria. People who didn’t experience one of the interventions were less motivated to exert physical effort to help climate causes than for when effort helped tackle starvation. However, some interventions presented before measuring motivation removed this bias, increasing relative motivation to benefit the environment.

 

The most effective idea presented to participants was to address psychological distance – the feeling that climate change doesn’t personally affect them or those around them. This intervention presented information about how climate change affected them locally for instance.  The second uses the psychology of system justification – the idea that the current system of living and doing things is the right one. This intervention showed how climate change threatened participants’ way of life, for example floods in the UK destroying Britons’ homes, and presented climate action as a patriotic act to prevent this.

 

Dr Jo Cutler from the University of Birmingham and a lead author of the paper said: “From cycling rather than driving to organising waste for recycling, many of the actions we can take to tackle climate change require us to exert physical effort. This global study found that participants around the world can be responsive to interventions that encourage climate action. We found that the most effective interventions were those that show climate change is already affecting people and their way of life may be changed or lost due to climate change. Interventions using this information led to participants being as willing to put in effort as for a more universally recognised cause like ending world hunger.”

 

“Lots of previous research on climate change simply asks people about their attitudes or behaviours they plan to do but there is no incentive for them to be honest. In our experiment, if people want to help, they have to work hard for it. We hope this approach will become more common in future work.”

 

Participants taking part in the study were asked a series of screening questions to assess their beliefs and attitudes about climate change, before taking part in tests to assess their willingness to act.

 

Participants were asked to make a physical effort to raise money for a climate-based charity, or a charity seeking to end world hunger. Prior to engaging in the physical effort, participants received one from a range of 11 different interventions (or none). The most successful interventions were::

• System justification: Text and images framed climate change as a threat to participants’ way of life and encouraged pro-environmental behaviour as patriotic; and
• Decreasing psychological distance. Climate change was presented as an immediate, local threat, and participants reflected on how it affects them personally.

Interventions that were less successful in overcoming bias include:

• Scientific consensus: Participants saw a message and graphic emphasising that 99% of climate scientists agree climate change is real and caused by humans; and
• Letter to future generations. Participants wrote a letter to a future child or other family member, describing their efforts to protect the planet and how they wish to be remembered.

 

The research team also found individual predictors of effort to help the environment included their personal belief that climate change is real and support for pro-environmental policies.

 

Professor Patricia Lockwood from the University of Birmingham and a senior author of the paper said: “As the world prepares to gather for COP30 in Brazil this year, individual and collective citizen action is an essential step towards making a meaningful difference to prevent climate change that affects every part of the world.

 

“Our findings show that despite how powerful some interventions might feel to sway us on climate action, when it comes to prosocial behaviour we as humans are by and large motivated by what feels immediate and close to us.

 

“Making climate action a patriotic duty for every citizen in every country around the world is a tool that we can adopt now to try to limit human-caused climate change.”

 

The study’s authors note that the paper doesn’t look at the difference in interventions between participants from different countries, due to the numbers of people taking part.

 

The University of Birmingham is leading research to help mitigate and adapt to the risks and impacts associated with climate change. The University has been awarded UNFCCC Observer Status which means that its experts can contribute to the vital discussions taking place at COP30.

 

Research at Birmingham, including at the Birmingham Institute for Sustainability and Climate Action addresses the reality of climate change through transforming health, environment, and society – sustainably supporting people and planet. Its researchers work with industry, academic and policy partners to accelerate progress on UN Sustainable Development Goals (SDGs) towards the 2030 Agenda.

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Journal

Communications Psychology

DOI

10.1038/s44271-025-00332-4 

Method of Research

Randomized controlled/clinical trial

Subject of Research

People

Article Title

Psychological interventions that decrease psychological distance or challenge system justification increase motivation to exert effort to mitigate climate change

Article Publication Date

5-Nov-2025