Wildfire smoke linked to declines in sperm quality

Wildfires don’t just cloud the skies, they may also affect fertility, a new study suggests.

University of Washington School of Medicine/UW Medicine

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As wildfires grow more frequent across the U.S. and Canada, their hidden toll may extend into the fertility clinic. A new study from UW Medicine suggests that wildfire smoke exposure may reduce key measures of sperm quality in patients undergoing fertility treatments. 

The research, published in Fertility and Sterility, encompassed an analysis of semen samples from 84 men who provided sperm for intrauterine insemination procedures between 2018 and 2022. Major wildfire smoke events in the Seattle area occurred in 2018, 2020 and 2022. By comparing semen analyses collected before and during wildfire seasons, the researchers were able to track changes in sperm health. 

“This study takes advantage of our institution’s location in the Puget Sound region, where wildfire smoke events create distinct pre- and post-exposure periods in a natural experiment to examine how a sudden, temporary decline in air quality influences semen parameters,” the authors wrote. 

The team found consistent declines in sperm concentration, total sperm count, total motile (movement-capable) sperm count, and total progressively motile sperm count during wildfire smoke exposure. One measure, the percentage of progressively motile sperm, showed a slight increase, though it was not enough to offset the overall reductions in sperm quality. 

Subjects served as their own control in this retrospective analysis of medical records across the smoke-event years. Findings were consistent across different wildfire years, showing that the results were not outliers, the authors added. 

“These results reinforce growing evidence that environmental exposures — specifically wildfire smoke — can affect reproductive health,” said senior author, Dr. Tristan Nicholson, an assistant professor of urology in the University of Washington School of Medicine and a reproductive urologist at the UW Medicine’s Men’s Health Center. Her patients are primarily men with infertility issues.  

The results align with prior smaller studies led by Oregon Health & Sciences University, which linked air pollution and wildfire smoke to impaired reproductive health. This underscores the need for further investigation, Nicholson said. 

“As we see more frequent and intense wildfire events, understanding how smoke exposure impacts reproductive health is critical.”  

Exposure to the very small particles in wildfire smoke has been linked to respiratory problems, heart attack, stroke, lung cancer and cognitive impairment. But the impact of the smoke exposure on human male fertility has not been well-characterized in the scientific literature. 

The researchers suggested that further study is needed of wildfire smoke’s impact on reproductive age, men versus women, and what happens to individuals trying to conceive if one or both have had wildfire smoke exposure.  

Although the study was not designed to evaluate the impact of wildfire smoke on reproductive outcomes, the pregnancy rate was 11% in the cohort of women with partners in this study, and the live birth rate was 9%, which tracks with similar rates previously published in literature and at the center, the authors note.  

One question unanswered by this study: Do sperm counts bounce back after smoke exposures? "We are very interested in how and when sperm counts recover after wildfire smoke exposure,” Nicholson said. “Currently we are conducting a prospective pilot study of men in the Seattle area to evaluate how wildfire smoke affects sperm quality.”  

She also has a joint appointment with UW Department of Occupational and Health Sciences in the School of Public Health. Nicholson is also a scholar in the UW Pediatric and Reproductive Environmental Health Scholars K12 program and a member of the UW Pediatric Environmental Health Specialty Unit. 

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Journal

Fertility and Sterility

DOI

10.1016/j.fertnstert.2025.08.031 

Method of Research

Experimental study

Subject of Research

People

Article Title

Wildfire smoke exposure is associated with decreased sperm concentration and total motile sperm count

Article Publication Date

1-Oct-2025

 

Native salt-tolerant plants help turn toxic bauxite waste into new soil

Biochar Editorial Office, Shenyang Agricultural University

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Early establishment of native halophytic plant species enhanced mineral weathering and organic carbon inputs in bauxite residue under field conditions
 

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Credit: Songlin Wu, Fang You, Lars Thomsen, David Parry & Longbin Huang

A team of researchers has found that hardy native plants could play a surprising role in transforming one of the aluminum industry’s most stubborn waste products into the beginnings of fertile soil.

Each year, alumina refineries generate millions of tons of bauxite residue, often called “red mud,” which is highly alkaline and difficult to rehabilitate. Stored in massive dams, this waste poses long-term environmental risks. Scientists have long searched for cost-effective ways to neutralize it and encourage vegetation growth.

In a new three-year field study, researchers from The University of Queensland tested whether native halophytic plants—species naturally adapted to salty, alkaline conditions—could kick-start the process of soil formation in seawater-treated bauxite residue. They focused on three species: Ruby saltbush (Enchylaena tomentosa), saltbush (Atriplex aminocola), and Rhodes grass (Chloris gayana).

The team found that the plants not only survived but actively altered the waste material. Their roots reduced the abundance of alkaline minerals such as sodalite, lowering pH levels from 9.5 to below 9.0. Advanced X-ray techniques revealed that the roots promoted the formation of new amorphous iron, aluminum, and silicon minerals. These minerals bound with organic compounds released by the plants, creating early organo-mineral associations that are essential for soil development.

At the same time, the plants more than doubled the total organic carbon content in the residue, from about 10 to over 20 milligrams per gram. This carbon came directly from root growth and exudates, which also fueled the stabilization of soil aggregates. Importantly, these effects were consistent across all three species, regardless of fertilizer inputs.

“Halophytic plants act as biological pioneers,” said Professor Longbin Huang, senior author of the study. “Their roots not only tolerate extreme conditions but actually drive chemical changes that make the residue less hostile and more soil-like.”

The findings suggest that introducing these native plants could serve as a low-cost, field-ready strategy to initiate the long process of converting red mud into functional soil. While the process is slow compared to adding large amounts of organic matter, it offers a sustainable interim solution in places where other amendments are impractical.

This research provides the first field-based evidence that native plants can spark the crucial early stages of soil formation in bauxite residue, pointing the way to greener rehabilitation of industrial waste landscapes.

 

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Journal reference: Wu S, You F, Thomsen L, Parry D, Huang L. 2025. Early establishment of native halophytic plant species enhanced mineral weathering and organic carbon inputs in bauxite residue under field conditions. Energy & Environment Nexus 1: e004 https://www.maxapress.com/article/doi/10.48130/een-0025-0006 

 

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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-0025-0006 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Early establishment of native halophytic plant species enhanced mineral weathering and organic carbon inputs in bauxite residue under field conditions

Article Publication Date

24-Oct-2025

 

Commercial sunbeds should be banned in the UK, say experts

Despite regulation, sunbeds remain popular with young people and are adding to the national skin cancer burden

BMJ Group

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Commercial sunbeds should be banned in the UK, argue experts in The BMJ today.

Using sunbeds causes melanoma and other skin cancers, particularly among young people, yet existing sunbed legislation is ineffective and there is little evidence that stricter rules would help protect the most vulnerable, say Professor Paul Lorigan and colleagues.

Indoor tanning is experiencing a boom in popularity, particularly among Gen Z (born 1997-2012), with social media promoting sunbeds as integral to wellness, they explain. For example, a 2024 survey of 2,003 people in the UK by Melanoma Focus found that 43% of respondents aged 18-25 used sunbeds, half of them at least weekly, with many unaware of the associated dangers.

And despite a ban on under 18s using sunbeds in England and Wales in 2011, a 2025 survey by Melanoma Focus of 100 UK 16-17 year olds found that 34% were still using sunbeds.

Neither the number nor location of sunbed outlets in the UK are monitored, point out the authors. Data from websites and social media in January 2024 identified 4,231 sunbed outlets in England and 232 in Wales, with density per 100,000 population highest in north west and north east England and in the most deprived areas.

The distribution of sunbed outlets also correlates with melanoma rates in young people, with the highest rates in north England, they add. Over 2,600 new diagnoses were recorded annually in 25-49 year olds in England during 2018-20, with two thirds of cases in women, and 146 deaths.

Regulation has also failed to prevent young people’s use of sunbeds in other countries, they note. For example, the percentage of under 18s using sunbeds in the Republic of Ireland has barely changed since stricter regulation in 2014, while Iceland’s 15-17 year olds are now the main users of sunbeds despite a ban for under 18s from 2011.

The current situation in the UK is “a clear example of an under-regulated industry aggressively marketing a harmful product to a vulnerable population,” they write. “An immediate outright ban on commercial sunbeds alongside public education offers the most cost effective solution to reduce skin cancer, save lives, and ease the burden on the NHS.”

To counter the economic impact of banning sunbeds on providers and communities, they suggest use of a buy-back scheme “to mitigate industry pushback and the potential effect on livelihoods.”

They conclude: “The UK government has pledged to prioritise prevention and to reduce health inequalities. Commercial sunbeds target those who are most disadvantaged and susceptible to harm.”

“Enhanced efforts to encourage sun safe behaviours are critically needed but will likely take a generation to have an effect. A ban on commercial sunbeds is the first step in this process. It would send a clear message and have an immediate effect on skin cancer.”

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Journal

The BMJ

DOI

10.1136/bmj-2025-085414 

Method of Research

Commentary/editorial

Subject of Research

People

Article Title

Commercial sunbeds should be banned in the UK

Article Publication Date

1-Oct-2025

COI Statement

Competing interests: We have read and understood BMJ policy on declaration of interests and have the following interests to declare: SK declares honoraria and travel support from Kyowa Kirin, Sanofi, and Sun Pharma, unrelated to the topic. IC is a patient advocate and trustee of Melanoma Focus. SD is chief executive of Melanoma Focus. PCL declares personal fees, advisory board fees, and travel support from MSD, Pierre Fabre, BMS, Iovance, and MLA Diagnostics and institutional support for research from BMS and Pierre Fabre, all unrelated to the topic, and wasthe previouschair of Melanoma Focus.

 

India could bear biggest impact from chikungunya, new maps suggest

London School of Hygiene & Tropical Medicine

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The most comprehensive mapping to date of the global risk of chikungunya suggests India could experience the greatest long-term impact from the mosquito-borne virus.

Based on existing evidence of chikungunya transmission, the infectious disease model predicts 14.4 million people could be at risk of infections globally each year, with 5.1 million people at risk in India. It’s likely that chikungunya cases could also spread to regions not currently recording infections or considered at-risk, the analysis found, potentially increasing the number of people at risk each year to 34.9 million globally, with 12.1 million in India.

India, Brazil and Indonesia also ranked as the top three countries most-likely to experience substantial long-term impacts from chikungunya, with India and Brazil accounting for 48% of the global impact of the disease on healthcare systems and individuals. The analysis suggests chronic health impacts will be the biggest concern, with existing evidence suggesting around 50% of people infected with the virus are left with long-term disability.

The authors say their analysis provides fresh information for public health professionals in the region, who are already working hard to contain chikungunya outbreaks.

The study, conducted by researchers from the London School of Hygiene & Tropical Medicine (LSHTM), Nagasaki University and the International Vaccine Institute in Seoul, mapped all possible regions where chikungunya infections could occur in future, to enable countries to prepare more effectively and estimated age-groups and areas most at risk of long-term effects, to target for possible vaccine programmes.

Chikungunya outbreaks are a growing public health concern and have been reported in over 114 countries since its re-emergence in 2004. The virus is spread by Aedes aegypti and Aedes albopictus mosquitoes, more commonly known as yellow fever and tiger mosquitoes, respectively, and causes severe joint pain and high fever (over 39℃) in those who become infected.

While most patients fully recover from the initial phase after a few weeks, over 50% of chikungunya patients who survive the infection suffer from long-term joint pain and disability, and cases can occasionally be fatal. There are currently no specific treatments for chikungunya but two preventative vaccines have been approved for use in some countries.

The study is the first of its kind to predict the burden of chikungunya using machine learning to combine existing data on chikungunya infections with other factors that may influence the likelihood of infections. This included: the likely occurrence of Aedes aegypti or Aedes albopicus mosquitoes; temperatures suitable for transmission of the virus by mosquitoes, modelled on the spread of dengue; annual precipitation in each region; how suitable different environments might be for the chikungunya virus to spread among populations; and national level Gross Domestic Product (GDP).

Studies have estimated chikungunya burden previously but have often relied on only surveillance and outbreak reports, which are known to be an underestimate of the true number of cases.

The model was first used to predict how many people at risk of chikungunya infections may actually become infected per year, based on the force of infection. For infectious diseases, a higher force of infection generally means a disease can spread more quickly, making explosive outbreaks more likely.

All continents had regions where high numbers of chikungunya infections were predicted annually. On average, between 1.2-1.3% of people at risk of chikungunya could expect to be infected per year, which is lower than the risk of dengue (6%). However, the data suggested certain countries, such as Gabon in Africa, could experience infections in up to 11% of people at risk.

The team then estimated the most likely long-term consequences of chikungunya infection for individuals and countries worldwide, known as its burden. India, Brazil and Indonesia were found to be the most at-risk of long-term impacts, mostly due to chronic disability experienced by many after infection, rather than death by acute infection. Chronic illness accounted for 54% of the chikungunya burden, mostly affecting those aged between 40 and 60 years, while children under 10 and adults over 80 were found to be the most at risk of acute illness.

Hyolim Kang, who led the study as part of her PhD at the London School of Hygiene  & Tropical Medicine (LSHTM), and who is also a Research Fellow at Nagasaki University, said: “It’s been widely thought that mosquitoes carrying chikungunya would be confined to subtropical or tropical continents, but our analysis has found that the risk extends way beyond these regions.

“Prevention of the spread of this disease is important for everyone. There are no specific antiviral therapies for chikungunya and treatment relies solely on supportive care. Not only are infections extremely painful, even the healthiest of people can be infected and left with life-long disability.”

Sushant Sahastrabuddhe, Associate Director General of Innovation, Initiatives, and Enterprise Development at the International Vaccine Institute , and co-author of the study, said: “The potential spread of vectors carrying viruses like chikungunya won’t wait for us to carry out years of research, so it’s been extremely important to us that the modelling we’re working on is shared and used in real time to help public health professionals manage current cases and prepare for the future.”

Kaja Abbas, joint Associate Professor at the London School of Hygiene & Tropical Medicine (LSHTM) and Nagasaki University, and senior author of the study, said: “Our model-based estimates are useful to inform outbreak response immunization strategies for different age groups using the two licensed vaccines (Ixchiq® and Vimkunya®) in Brazil and broadly in any setting globally at risk of chikungunya outbreaks. We hope other countries will follow suit and look to prioritise regions conventional surveillance systems may have missed.”

The team say their maps are a snapshot representing the long-term annual average, and do not account for unexpected changes likely to be recorded going forward, such as extreme weather events and possible changes due to climate change.

The researchers hope their findings can inform prevention strategies across the globe, for example by the WHO SAGE Working Group on Chikungunya Vaccines, to identify countries or regions at risk of long-term burden from chikungunya and to support geographical prioritisation.

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Journal

BMJ Global Health

Method of Research

Computational simulation/modeling

Article Title

Global, regional, and national burden of chikungunya: force of infection mapping and spatial modelling study’

Article Publication Date

1-Oct-2025