Environment and health – Cabot Institute for the Environment blog

The role of carbon dioxide in airborne disease transmission: a hidden key to safer indoor spaces

Posted on April 23, 2025 by amanda.woodman-hardy

We’ve long known that environmental factors – from humidity and temperature to trace chemical vapours – can influence how pathogens, such as viruses, bacteria and fungi, behave once released into the air. These tiny droplets of respiratory fluid, or aerosols, carry viruses and bacteria and can float for minutes or even hours. But while we’ve been busy focusing on physical distancing and surface cleaning, a quieter factor may have been playing a much bigger role in airborne disease transmission all along: carbon dioxide (CO₂).

During the pandemic, we studied what happens to a virus when it travels through the air in tiny droplets from our breath – known as aerosols. In earlier research, we found that the droplet’s pH (how alkaline it is) can affect how quickly the virus loses its ability to infect people. Our more recent research, though, suggests that CO₂ levels in indoor air may significantly affect how long viruses survive once airborne – and the implications are profound.

Airborne virus survival

When someone coughs, sneezes, talks or sings, they release microscopic droplets into the air. These droplets start out in a warm, moist and CO₂-rich environment inside the lungs, where CO₂ levels reach a staggering 38,000 parts per million (ppm). Once expelled, they encounter the cooler, drier and typically much lower-CO₂ environment of indoor or outdoor air. This rapid change triggers a chain reaction inside the droplet.

One key component inside these droplets is bicarbonate, which acts as a buffer and is formed when CO₂ dissolves in liquid. As CO₂ diffuses out of the droplet into the air, bicarbonate leaves with it. This causes the droplet’s pH to rise – becoming increasingly alkaline, sometimes reaching pH 10.

Why does this matter? Viruses like COVID-19 don’t like alkaline environments. As the pH rises, their ability to infect decreases. In other words, the higher the pH, the quicker the virus becomes inactive. However, when the ambient CO₂ concentration is high, this pH shift is delayed or minimised, meaning the virus remains in a more hospitable environment – and stays infectious longer.

What role does CO₂ play?

While CO₂ doesn’t transmit viruses itself, it acts as a proxy for indoor crowding and poor ventilation. The more people in a space, the more CO₂ builds up from exhaled breath. When there isn’t enough ventilation, these levels stay high as do the chances that airborne viruses can linger longer and infect others.

Outdoor CO₂ levels are around 421ppm, but in crowded or poorly ventilated spaces, indoor levels can easily exceed 800ppm. That’s the tipping point identified in the study, where the air starts allowing droplets to maintain a lower pH, increasing the survival time of viruses. In the 1940s, global CO₂ levels were much lower – around 310ppm – meaning indoor air offered less of a survival advantage to airborne pathogens.

Looking ahead, climate projections estimate CO₂ levels could reach 685ppm by 2050, making this issue not only one of pandemic response but also of climate and public health policy. If we don’t address this now, we may be heading into a future where viruses survive longer in the air due to everyday indoor conditions.

Can we fix it?

The good news? These findings suggest solutions we can implement right now.

First, improve indoor ventilation. Increasing airflow and introducing outdoor air into enclosed spaces dilutes both CO₂ levels and any virus-containing aerosols. This simple change can significantly reduce the risk of airborne transmission – not just for COVID-19, but for future respiratory viruses as well.

And, in the not-too-distant future, we might have indoor carbon capture technology. These devices, which are still being developed, could help remove excess CO₂ from the air, especially in hospitals, classrooms and public transport where the risk of spreading illness is higher.

Also, monitoring indoor CO₂ levels using affordable sensors can empower individuals, schools and businesses to assess the indoor air quality and adjust the ventilation accordingly. If CO₂ levels rise above safe thresholds (often considered about 800ppm), it’s time to open windows, use air purifiers or ask some people to leave the room.

This research reshapes the way we think about air quality. It’s no longer just about stuffiness or comfort – it’s about infection risk. As we face rising global CO₂ levels and continue to recover from the COVID pandemic, it’s clear that managing indoor air environments is essential to public health.

By taking CO₂ seriously – not just as a climate metric but as a health indicator – we have a unique opportunity to reduce disease transmission in our everyday environments. Because when it comes to viruses in the air, the air itself might be our greatest ally – or our biggest threat.

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This blog is written by Dr Allen Haddrell, Research Fellow, School of Chemistry, University of Bristol and Dr Henry Oswin, Postdoctoral Research Fellow, Faculty of Science, School of Earth & Atmospheric Sciences, Queensland University of Technology. This article is republished from The Conversation under a Creative Commons license. Read the original article.

‘Heavy metals’ contaminate 17% of the world’s croplands, say scientists

Posted on April 23, 2025 by amanda.woodman-hardy

arsenic poisoning showing as black spots on a persons hands. — Arsenic poisoning. Image credit: Anita Ghosh-REACH

Nearly 17% of the world’s croplands are contaminated with “heavy metals”, according to a new study in Science. These contaminants – arsenic, cadmium, lead, and others – may be invisible to the eye, but they threaten food safety and human health.

Heavy metals and metalloids are elements that originate from either natural or human-made sources. They’re called “heavy” because they’re physically dense and their weight is high at an atomic scale.

Heavy metals do not break down. They remain in soils for decades, where crops can absorb them and enter the food chain. Over time, they accumulate in the body, causing chronic diseases that may take years to appear. This is not a problem for the distant future; it’s already affecting food grown today.

Some heavy metals, such as zinc and copper, are essential micronutrients in trace amounts. Others – including arsenic, cadmium, mercury, and lead – are toxic even at low concentrations.

Some are left behind by natural geology, others by decades of industrial and agricultural activities. They settle into soils through mining, factory emissions, fertilisers or contaminated water.

When crops grow, they draw nutrients from the soil and water – and sometimes, these contaminants too. Rice, for instance, is known for taking up arsenic from flooded paddies. Leafy greens can accumulate cadmium. These metals do not change the taste or colour of food. But they change what it does inside the body.

The quiet health crisis beneath our crops

Long-term exposure to arsenic, cadmium, or lead has been linked to cancer, kidney damage, osteoporosis, and developmental disorders in children. In regions where local diets rely heavily on a single staple crop like rice or wheat, the risks multiply.

The Science study, led by Chinese scientist Deyi Hou and his colleagues, is one of the most comprehensive mapping efforts. By combining recent advances in machine learning with an expansive dataset of 796,084 soil concentrations from 1,493 studies, the authors systematically assessed global soil pollution for seven toxic metals: arsenic, cadmium, cobalt, chromium, copper, nickel, and lead.

The study found that cadmium in agricultural soil frequently exceeded the threshold, particularly in the areas shaded in red in this map:

shaded world map — A map of the aggregate distribution of seven heavy metals reveals lots of hotspots around the world.
Hou et al / Science

The authors also describe a “metal-enriched corridor” stretching from southern Europe through the Middle East and into south Asia. These are areas where agricultural productivity overlaps with a history of mining, industrial activity and limited regulation.

How science is reading the soil’s story

Heavy metal contamination in cropland varies by region, often shaped by geology, land use history, and water management. Across central and south-east Asia, rice fields are irrigated with groundwater that naturally contains arsenic. That water deposits arsenic into the soil, where it is taken up by the rice.

Fortunately, nature often provides defence. Recent research showed that certain types of iron minerals in the soil can convert arsenite – a toxic, mobile form of arsenic – into arsenate, a less harmful species that binds more tightly to iron minerals. This invisible soil chemistry represents a safety net.

In parts of west Africa, such as Burkina Faso, arsenic contamination in drinking and irrigation water has also affected croplands. To address this, colleagues and I developed a simple filtration system using zerovalent iron – essentially, iron nails. These low-cost, locally sourced filters have shown promising results in removing arsenic from groundwater.

In parts of South America, croplands near small-scale mines face additional risks. In the Amazon basin, deforestation and informal gold mining contribute to mercury releases. Forests act as natural mercury sinks, storing atmospheric mercury in biomass and soil. When cleared, this stored mercury is released into the environment, raising atmospheric levels and potentially affecting nearby water bodies and croplands.

Cropland near legacy mining sites often suffers long-term contamination but with the appropriate technologies, these sites can be remediated and even transformed into circular economy opportunities.

Evidence-based solutions

Soil contamination is not just a scientific issue. It’s a question of environmental justice. The communities most affected are often the least responsible for the pollution. They may farm on marginal lands near industry, irrigate with unsafe water, or lack access to testing and treatment. They face a double burden: food and water insecurity, and toxic exposure.

There is no single fix. We’ll need reliable assessment of contaminated soils and groundwater, especially in vulnerable and smallholder farming systems. Reducing exposure requires cleaner agricultural inputs, improved irrigation, and better regulation of legacy industrial sites. Equally critical is empowering communities with access to information and tools that enable them to farm safely.

Soils carry memory. They record every pollutant, every neglected regulation, every decision to cut corners. But soils also hold the potential to heal – if given the proper support.

This is not about panic. It’s about responsibility. The Science study provides a stark but timely reminder that food safety begins not in the kitchen or market but in the ground beneath our feet. No country should unknowingly export toxicity in its grain, nor should any farmer be left without the tools to grow food safely.

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This blog is written by Dr Jagannath Biswakarma, Senior Research Associate, School of Earth Sciences and Cabot Institute for the Environment, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

How a lack of period product regulation harms our health and the planet

Posted on April 4, 2025 by amanda.woodman-hardy

Did you know that in the UK period products are regulated under the same consumer legislation as candles? For 15 million people who menstruate each month, these items are used internally or next to one of the most sensitive parts of the body for extended times.

Consumers should be entitled to know what is in their period products before choosing which ones to buy. Yet, because of the current lack of adequate regulation and transparency, manufacturers are not required to disclose all materials. And only basic information is available on brand websites. Campaigners are now calling for better regulation.

Independent material testing shows that single-use period pads can contain up to 90% plastic. An estimated 4.6 million pads, tampons and panty liners are flushed away daily in the UK. These contribute to blocked sewers and fatbergs. They also pollute rivers and oceans.

Meanwhile, reusable period products are promoted by aid charities as a way to tackle period poverty and reduce waste. But independent tests by organisations such as Which? have found harmful chemicals inside both single-use and reusable period products.

These include synthetic chemicals that disrupt hormones – known as endocrine-disrupting chemicals – and forever chemicals or per- and polyfluoroalkyl substances (PFAS) that don’t degrade. These chemicals have been associated with a range of health harms from cancers to reproductive disorders and infertility. They have no place in period products.

I work as a women’s health researcher at the University of Bristol’s Digital Footprints Lab alongside a team of data scientists. We harness digital data, such as shopping records, to study public health issues. My research looks at how things like education affect which menstrual products people choose.

In collaboration with the charity Women’s Environmental Network, I am exploring intersections between gender, health, equity and environmental justice – especially among marginalised women and communities. But social stigma prevents open discussions about menstruation and how best to improve period product regulation.

Menstrual stigma influences everything from the information and support people who menstruate receive to the types of products we use and how we dispose of them. In a study of menstrual education experiences in English schools, my colleague and I found evidence of teacher attitudes perpetuating menstrual stigma.

Lessons typically lacked content about the health or environmental consequences of period products. Our study showed that just 2.4% of 18- to 24-year-olds surveyed were taught about sustainable alternatives to single-use tampons and menstrual pads.

four women sat looking at period product information — An environmenstrual workshop hosted by the charity, Women’s Environmental Network.
Women’s Environmental Network / Sarah Larby, CC BY-NC-ND

For decades, period product adverts portrayed menstrual blood as a blue liquid. The social taboos around periods, largely created and reinforced by period brands over decades of fear-based marketing, has left its mark.

For example, in response to customer’s anxieties about supposed menstrual odour, manufacturers are increasingly using potentially environmentally harmful antimicrobials like silver and anti-odour additives in period products. This is despite there being no evidence that period products such as menstrual pants or pads transmit harmful bacteria that need sanitising. The silver also washes out after a couple of washes.

The role of regulation

In New York state, the Menstrual Products Right To Know Act means that a period product cannot be sold unless the labelling includes a list of materials. In Scotland, a government initiative provides free period products to anyone who needs them.

Catalonia in Spain has introduced a groundbreaking law that ensures access to safe and sustainable period products, while also working to reduce menstrual stigma and taboos through education.

A new European “eco label” is a step forward, but companies don’t have to use it. This voluntary label, which shows a product is good for the environment, doesn’t cover period underwear.

Now, campaigners at the Women’s Environmental Network are calling for the UK government to adopt a Menstrual Health, Dignity and Sustainability Act, backed by many charities, academics and environmentalists. This will enable equal access to sustainable period products, improved menstrual education, independent testing, transparent product labelling and stronger regulations.

The regulation of period products is currently being considered as part of the product regulation and metrology bill and the use of antimicrobials in period products is being included in the consumer products (control of biocides) bill introduced by Baroness Natalie Bennett. By tackling both health implications and environmental harms, period products can be produced in a safer way, for both people and planet.

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This blog is written by Poppy Taylor, PhD Candidate, Women’s Health, Bristol Medical School, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.