The metals have previously been shown to damage the health of pollinators, which ingest them in nectar as they feed, leading to reduced population sizes and death. Even low nectar metal levels can have long-term effects, by affecting bees’ learning and memory - which impacts their foraging ability.

Researchers have found that common plants including white clover and bindweed, which are vital forage for pollinators in cities, can accumulate arsenic, cadmium, chromium and lead from contaminated soils.

Metal contamination is an issue in the soils of cities worldwide, with the level of contamination usually increasing with the age of a city. The metals come from a huge range of sources including cement dust and mining.

The researchers say soils in cities should be tested for metals before sowing wildflowers and if necessary, polluted areas should be cleaned up before new wildflower habitats are established.

The study highlights the importance of growing the right species of wildflowers to suit the soil conditions. 

Reducing the risk of metal exposure is critical for the success of urban pollinator conservation schemes. The researchers say it is important to manage wildflower species that self-seed on contaminated urban land, for example by frequent mowing to limit flowering - which reduces the transfer of metals from the soil to the bees.

The results are published today in the journal Ecology and Evolution. 

Dr Sarah Scott in the University of Cambridge’s Department of Zoology and first author of the report, said: “It’s really important to have wildflowers as a food source for the bees, and our results should not discourage people from planting wildflowers in towns and cities.

“We hope this study will raise awareness that soil health is also important for bee health. Before planting wildflowers in urban areas to attract bees and other pollinators, it’s important to consider the history of the land and what might be in the soil – and if necessary find out whether there’s a local soil testing and cleanup service available first.”

The study was carried out in the post-industrial US city of Cleveland, Ohio, which has over 33,700 vacant lots left as people have moved away from the area. In the past, iron and steel production, oil refining and car manufacturing went on there. But any land that was previously the site of human activity may be contaminated with traces of metals.

To get their results, the researchers extracted nectar from a range of self-seeded flowering plants that commonly attract pollinating insects, found growing on disused land across the city. They tested this for the presence of arsenic, cadmium, chromium and lead. Lead was consistently found at the highest concentrations, reflecting the state of the soils in the city.

The researchers found that different species of plant accumulate different amounts, and types, of the metals. Overall, the bright blue-flowered chicory plant (Cichorium intybus) accumulated the largest total metal concentration, followed by white clover (Trifolium repens), wild carrot (Daucus carota) and bindweed (Convolvulus arvensis). These plants are all vital forage for pollinators in cities - including cities in the UK - providing a consistent supply of nectar across locations and seasons.

There is growing evidence that wild pollinator populations have dropped by over 50% in the last 50 years, caused primarily by changes in land use and management across the globe. Climate change and pesticide use also play a role; overall the primary cause of decline is the loss of flower-rich habitat.

Pollinators play a vital role in food production: many plants, including apple and tomato, require pollination in order to develop fruit. Natural ‘pollination services’ are estimated to add billions of dollars to global crop productivity. 

Scott said: “Climate change feels so overwhelming, but simply planting flowers in certain areas can help towards conserving pollinators, which is a realistic way for people to make a positive impact on the environment.”

The research was funded primarily by the USDA National Institute of Food and Agriculture.

Reference 
Scott, S.B.& Gardiner, M.M.: ‘Trace metals in nectar of important urban pollinator forage plants: A direct exposure risk to pollinators and nectar-feeding animals in cities.’ Ecology and Evolution, April 2025.  DOI: 10.1002/ece3.71238
 

Wildflowers growing on land previously used for buildings and factories can accumulate lead, arsenic and other metal contaminants from the soil, which are consumed by pollinators as they feed, a new study has found.

Our results should not discourage people from planting wildflowers in towns and cities. But.. it’s important to consider the history of the land and what might be in the soil."Sarah ScottSarah ScottChicory growing in a vacant lot

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UCAS evaluation shows the most engaged sixth formers saw their results jump by a grade on average, were up to four times as successful in achieving an A*, and around twice as successful in securing an Oxbridge place.

Rebalancing the planet must happen faster. Cambridge researchers are using AI to help.  

A major review of over 67,000 animal species has found that while the natural world continues to face a biodiversity crisis, targeted conservation efforts are helping bring many species back from the brink of extinction.

Charlotte Andrew is a PhD student in the Insect Biomechanics Group in the Department of Zoology. Her research explores the mechanical implications of weather conditions on insect trapping in carnivorous plants.

The pledge, made in February 2020 by the UK’s nine leading game shooting and rural organisations, aimed to benefit wildlife and the environment and ensure a market for the healthiest game meat food products. 

But a Cambridge team, working with the University of the Highlands and Islands, has consistently shown that lead shot was not being phased out quickly enough to achieve a complete voluntary transition to non-toxic ammunition by 2025. In a final study, published today in the journal Conservation Evidence, the team concludes that the intended transition has failed.

The team has closely monitored the impact of the pledge every year since its introduction, recruiting expert volunteers to buy whole pheasants from butchers, game dealers and supermarkets across Britain and recover embedded shotgun pellets for analysis. 

In 2025, the study - called SHOT-SWITCH - found that of 171 pheasants found to contain shot, 99% had been killed with lead ammunition. 

This year, for the first time, the team also analysed shotgun pellets found in red grouse carcasses shot in the 2024/25 shooting season and on sale through butchers’ shops and online retailers. In all 78 grouse carcasses from which any shot was recovered, the shot was lead. 

“Many members of the shooting community had hoped that the voluntary pledge away from lead ammunition would avert the need for regulation. But the voluntary route has now been tested - with efforts made by many people - and it has not been successful,” said Professor Rhys Green in the University of Cambridge’s Department of Zoology and lead author of the report.

Eating game meat killed using lead shot will expose people unnecessarily to additional dietary lead. Lead is toxic to humans even in very small concentrations; the development of the nervous system in young and unborn children is especially sensitive to its effects. As a result, many food safety agencies now advise that young children and pregnant women should avoid, or minimise, eating game meat from animals killed using lead ammunition.

Discarded shot from hunting also poisons and kills many tens of thousands of the UK’s wild birds each year.

Despite proposing the voluntary change, many shooting organisations and some individual shooters do not support proposed regulatory restrictions on lead ammunition.

Green said: “Private individuals pay a lot of money to shoot pheasants on some private estates - and people don’t like to change their habits. It’s a bit like wearing car seatbelts, or not smoking in pubs. Despite the good reasons for doing these things, some people were strongly against using regulation to achieve those changes, which are now widely accepted as beneficial. The parallel with shooting game with lead shotgun ammunition is striking.” 

Danish shooters now say that the legal ban on lead introduced in Denmark around 30 years ago was justified. They say it has not reduced the practicality or popularity of their sport, and has increased its acceptability to wider society.

“Although a few large UK estates have managed to enforce non-lead ammunition on pheasant shoots, some have had to be quite draconian in order to do it, with the estate gamekeepers insisting on loading the guns for the shooters,” added Green.

In the 2020/21 and 2021/22 shooting seasons, over 99% of the pheasants studied were shot using lead ammunition. This figure dropped slightly to 94% in 2022/23 and 93% in 2023/24, with the remaining pheasants killed by ammunition made of steel or a metal called bismuth, before rising to 99% again in 2024/25.

Retail pressure

The researchers also checked up on a pledge made by Waitrose in 2019 to stop selling game killed with lead ammunition. 

They found that the retailer had been largely let down by suppliers, and that some of their shooters continued to shoot using lead despite making assurances to the contrary. As a result, Waitrose did not sell oven-ready pheasants at all between 2021 and 2023. It sold pheasants again in January 2024 and the 2024/25 season, but the researchers showed that the majority had been killed using lead shot.

In 2022 the National Game Dealers Association (NGDA), which buys game and sells it to the public and food retailers, also announced it would no longer sell game of any kind that had been shot using lead ammunition. But this pledge has since been withdrawn. The researchers bought 2024/25 season pheasants from three NGDA member businesses and found that all had been shot with lead ammunition.

Inside influence 

The researchers also analysed all articles relating to the voluntary transition published in the magazine of the UK’s largest shooting organisation, the British Association for Shooting and Conservation. They found that articles near the beginning of the five-year pledge communicated clear, frequent and positive messages about the effectiveness and practicality of non-lead shotgun ammunition.

But by 2023, mentions of the transition and encouragement to follow it had dropped dramatically. 

The upshot

At the request of the Defra Secretary of State, the UK Health & Safety Executive (HSE) has assessed the risks to the environment and human health posed by lead in shot and bullets. Its report, published in December 2024, proposes that the UK Government bans the use of lead shot and large calibre bullets for game shooting because of the risks they pose to the environment and health. This recommendation is currently under review by Defra ministers, with a response due in March 2025.

Steel shotgun pellets are a practical alternative to lead and can be used in the vast majority of shotguns, as can other safe lead-free alternatives. But the results of this study indicate UK hunters remain unwilling to make the switch voluntarily.

Since 2010, UK governments have preferred voluntary controls over regulation in many areas of environment and food policy and have suggested that regulation be used only as a last resort.

“Shooting organisations did a lot of questionnaire surveys when the pledge was introduced in 2020, and the results suggested many shooters thought the time had come to switch away from lead ammunition. Those responses stand in contrast to what we’ve actually measured for both pheasant and grouse,” said study co-author Dr Mark Taggart at the University of the Highlands and Islands.

Toxic lead

A previous study led by Green and colleagues found that pheasants killed by lead shot contained many fragments of lead too small to detect by eye or touch, and too distant from the shot to be removed without throwing away a large proportion of otherwise useable meat. This means that eating pheasant killed using lead shot is likely to expose consumers to raised levels of lead in their diet, even if the meat is carefully prepared to remove whole shotgun pellets and the most damaged tissue.

Lead has been banned from use in paint and petrol for decades. It is toxic to humans when absorbed by the body and there is no known safe level of exposure. Lead accumulates in the body over time and can cause long-term harm, including increased risk of cardiovascular disease and kidney disease in adults. Lead is known to lower IQ in young children and affect the neurological development of unborn babies.

The studies were part-funded by the RSPB, Waitrose & Partners, and an anonymous donor. They were supported by a group of unpaid volunteers, who are co-authors of the reports.
 

References

Green, R.E. et al: ‘The proportion of common pheasants shot using lead shotgun ammunition in Britain has barely changed despite five years of voluntary efforts to switch from lead to non-lead ammunition.’ March 2025, Conservation Evidence. DOI: 10.52201/CEJ22/EXYS6184

Green, R.E. et al.: ‘Sampling of red grouse carcasses in Britain indicates no progress during an intended five-year voluntary transition from lead to non-lead shotgun ammunition.’ February 2025, Conservation Evidence. DOI: 10.52201/CEJ22/YYWM1722
 

A voluntary pledge made by UK shooting organisations in 2020 to replace lead shot with non-toxic alternatives by 2025 has failed, analysis by Cambridge researchers finds.

The voluntary route has now been tested - with efforts made by many people - and it has not been successful.Rhys GreenAndy Hay, RSPBAdult pheasant

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Duygu Sevilgen has built a coral lab in the basement of an old Zoology building. Here, 10 experimental tanks host multicoloured miniature forests, with each tank representing a different marine environment. Duygu uses extremely small sensors to record the fine details of coral skeletons and listen to their dialogue with algae. In doing so, she determines how much change corals can bear, and improves our chances of saving them in the wild.

Some efforts to preserve or rewild natural habitats are shifting harmful land use to other parts of the world – and this could drive an even steeper decline in the planet’s species, according to a team of conservation scientists and economists led by the University of Cambridge.   

Researchers from over a dozen institutions worldwide have come together to call on the global community to acknowledge the “biodiversity leak”: the displacement of nature-damaging human activities caused by ringfencing certain areas for protection or restoration.

They argue that rewilding productive farmland or forestry in industrialised nations that have low levels of biodiversity may do more harm than good on a planetary scale.

Exploratory analysis by the team suggests that reclaiming typical UK cropland for nature may be five times more damaging for global biodiversity than the benefit it provides local species, due to the displacement of production to more biodiverse regions.   

While this “leakage” has been known about for decades, it is largely neglected in biodiversity conservation, say the researchers. They argue it undermines actions ranging from establishing new nature reserves to the EU’s environmental policies.

Writing in the journal Science, the experts point out that even the UN’s landmark Global Biodiversity Framework – aiming for 30% of the world’s land and seas to be conserved – makes no mention of the leakage problem.

“As nations in temperate regions such as Europe conserve more land, the resulting shortfalls in food and wood production will have to be made up somewhere,” said Prof Andrew Balmford, from the University of Cambridge’s Department of Zoology. 

“Much of this is likely to happen in more biodiverse but often less well-regulated parts of the world, such as Africa and South America. Areas of much greater importance for nature are likely to pay the price for conservation efforts in wealthy nations unless we work to fix this leak.”

“The first thing we need to do is collectively acknowledge that these leaks exist,” said co-author Prof Brendan Fisher from the University of Vermont. “If protesting a logging concession in the US increases demand for pulp from the tropics, then we are unlikely to be helping biodiversity.”

Co-author Dr Ben Balmford of the University of Exeter said: “This issue demands far greater attention from a sector that seeks to shape how 30% of an ever hungrier and more connected planet is managed.”

‘Leakage’ is already a major issue for carbon credits tied to forest preservation, say researchers. But they argue it’s a real problem for biodiversity conservation efforts too.

While protected areas can slow deforestation inside their borders, there’s evidence it can simply shift to neighbouring areas. Production can also be displaced much further. Efforts to protect the Pacific Northwest’s old-growth forests resulted in increased logging in other North American regions, for example.

Yet a survey of site managers of tropical conservation projects conducted by the Cambridge team found that 37% had not come across the concept of leakage, and less than half of the projects were attempting to curb any displacement damage.*

The researchers explored how leakage caused by protected areas could affect global biodiversity by applying real-world food and biodiversity data to two hypothetical conservation projects.

They found that rewilding a sizeable area of Brazilian soybean farms would push production to nations such as Argentina and USA, but because Brazil is so important for biodiversity, the local conservation gains could be around five times greater than the displacement harms.

The opposite would be true if the equivalent area of UK arable farmland was reclaimed for nature. Here, production would be displaced to Australia, Germany, Italy and Ukraine.**

As the UK has fewer species than these other countries, damage from ‘leakage’ could be five times greater than the local benefit to British biodiversity. 

The experts offer a number of ways to help plug the biodiversity leak. They call on governments and the conservation sector to take leakage far more seriously when making environmental policy at national and global level.

They also point out that leakage could be reduced if conservation projects work with others to reduce demand – especially for high-footprint commodities such as red meat.

There’s scope to limit leakage by targeting conservation to areas high in biodiversity but where current or potential production of food or timber is limited, say researchers. One example is restoring abandoned tropical shrimp farms to mangroves.

However, we should also be much more cautious about restoring natural habitats on currently productive farmland in less biodiverse parts of the world, they argue.

Beyond planning where to conserve, major conservation initiatives should work with partners in other sectors to support local farmers, so that overall levels of production are maintained in the region despite protected areas. The team cite examples ranging from forest-friendly chocolate to herding practices that protect snow leopards.

Where local yield increases are difficult, larger-scale programmes could establish long-range partnerships with suppliers in the same markets to make up shortfalls in production.

“Without attention and action, there is a real risk that the biodiversity leak will undermine hard-won conservation victories,” said co-author Dr Fiona Sanderson of the Royal Society for Protection of Birds, who works on reducing the impacts of cocoa production in Sierra Leone.

Lead author from Cambridge, Prof Andrew Balmford, added: “At its worst, we could see some conservation actions cause net global harm by displacing production to regions which are much more significant for biodiversity.” 

*Survey of 100 practitioners involved in area-based tropical conservation projects, including directors, managers, coordinators, and researchers. Respondents came from 36 countries across all five continents. Further details: https://zenodo.org/records/14780198

** Two hypothetical habitat restoration programs covering 1000km2 of Brazilian soy-producing land, and restoring 1000km2 of arable farmland in the UK that produces wheat, barley and oilseed rape.

Researchers call on the international community to recognise and start tackling the “biodiversity leak”. 

Areas of much greater importance for nature are likely to pay the price for conservation efforts in wealthy nations unless we work to fix this leakAndrew BalmfordMichael Duff, © RSPB-images.comThe Gola Rainforest Project in Sierra Leone. This conservation project has limited leakage while slowing deforestation by supporting nearby farmers such as Mallo Samah to increase their yields and get higher prices for their cocoa.

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Invasive pests are slipping unnoticed into northern Europe in huge shipments of cut flowers and potted plants, say researchers, with potential to damage food crops and the natural environment