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.”

“I was very surprised by our findings. As far as I know, no one has previously discovered molecules like these bile acids that can interact with the androgen receptor in this way,” said co-senior author Dr. Chun-Jun Guo, an associate professor of immunology in medicine in the Division of Gastroenterology and Hepatology and a scientist at the Jill Roberts Institute for Research in Inflammatory Bowel Disease at Weill Cornell Medicine.

Dr. David Artis, director of the Jill Roberts Institute and the Friedman Center for Nutrition and Inflammation and the Michael Kors Professor in Immunology, and Dr. Nicholas Collins, assistant professor of immunology in medicine, both at Weill Cornell Medicine, are co-senior authors of the study. Drs. Wen-Bing Jin, formerly a postdoctoral associate, and Leyi Xiao, a current postdoctoral associate in Dr. Guo’s lab, are the co-first authors of the study.

Primary bile acids are produced by the liver and released into the gut, where diverse groups of bacteria work together to modify their chemical structures. Researchers suspected these gut microbial modifications could affect how bile acids function and interact with human signaling pathways. To test this idea, the investigators set out to explore the full extent of bacterial modifications to bile acids and understand how these changes affect their biological roles.

It turns out that gut bacteria have remarkable potential to transform bile acids. “We discovered more than fifty different bile acid molecules modified by the microbiota — many of which had never been identified before,” said Dr. Guo, who is also the Halvorsen Family Research Scholar in Metabolic Health at Weill Cornell Medicine.

These newly uncovered structures could open the door to new biological insights-particularly in how they interact with human receptors that sense bile acids. Given that bile acids share the same steroid backbone as sex hormones like testosterone and estrogen, the structural resemblance raised an intriguing question for the researchers: could these microbially modified bile acids also interact with sex hormone receptors in the body? “It seemed like a wild idea at the time,” Dr. Guo said.

Surprisingly, the answer appears to be yes. When the investigators tested the 56 altered bile acids that they discovered, they found one that antagonizes the androgen receptor — a molecule that interacts with sex hormones to regulate many aspects of human development. When they tested an additional 44 microbiota-modified bile acids that had previously been characterized, the team found three more that act similarly. This unexpected finding raised exciting new questions for the team: which specific cells were affected by the altered bile acids — and what biological functions these modified molecules might influence.

In addition to its role in development, the androgen receptor is also found in certain immune cells, including CD8 T cells. Previous studies have shown that blocking this receptor can enhance the ability of these immune cells to fight tumors. The investigators wondered whether the bile acids could replicate this effect by binding to and inactivating the androgen receptor. To test the idea, they treated mice with bladder cancer using these compounds — and observed a potent anti-tumor response. Further analysis revealed that the modified bile acids specifically boosted the activity of T cells — the immune cells best equipped to kill cancer.

“Our results suggest that these altered bile acids help shrink tumors by enhancing T cells’ ability to survive within the tumor and destroy cancer cells,” Dr. Collins said.

“This study highlights the profound and evolving partnership between the human host and its gut microbiota, emphasizing the importance of integrating microbial activity into the design of future cancer therapies.” Dr. Artis said. “It also exemplifies the power of multidisciplinary collaboration in driving microbiome science toward deeper molecular understanding of host-microbe interactions.”

This discovery opens up exciting new possibilities for boosting tumor-killing immune response. Potential approaches include introducing targeted gut microbes to cancer patients before therapy, or directly administering the anti-cancer bile acids as part of treatment, the researchers suggested. Although these compounds still need to be tested in humans, the team is optimistic that bile acids could eventually become a key component of effective cancer therapies — especially when combined with existing treatments for a more powerful impact.

However, important questions remain. For example, how might diet — which is known to influence microbiota composition — affect the production of these bile acids? And beyond their anti-cancer properties, what physiological effects might these androgen receptor-blocking bile acids have in healthy individuals? The team is now focused on precisely controlling the synthesis and release of these beneficial molecules using advanced techniques to genetically engineer gut commensal bacteria, aiming to understand the broader physiological impact in the host initiated by these androgen blocking, microbiota-derived bile acids.

Planetary scientists at the University of California, Berkeley, now say that hailstorms of mushballs accompanied by fierce lightning actually exist on Jupiter. In fact, mushball hailstorms may occur on all gaseous planets in the galaxy, including our solar system’s other giant planets, Saturn, Uranus and Neptune.

The idea of mushballs was initially put forth in 2020 to explain nonuniformities in the distribution of ammonia gas in Jupiter’s upper atmosphere that were detected both by NASA’s Juno mission and by radio telescopes on Earth.

At the time, UC Berkeley graduate student Chris Moeckel and his adviser, Imke de Pater, professor emerita of astronomy and of earth and planetary science, thought the theory too elaborate to be real, requiring highly specific atmospheric conditions.

“Imke and I both were like, ‘There’s no way in the world this is true,'” said Moeckel, who received his UC Berkeley Ph.D. last year and is now a researcher at UC Berkeley’s Space Sciences Laboratory. “So many things have to come together to actually explain this, it seems so exotic. I basically spent three years trying to prove this wrong. And I couldn’t prove it wrong.”

The confirmation, reported March 28 in the journal Science Advances, emerged together with the first 3D visualization of Jupiter’s upper atmosphere, which Moeckel and de Pater recently created and describe in a paper that is now undergoing peer review and is posted on the preprint server arXiv.

The 3D picture of Jupiter’s troposphere shows that the majority of the weather systems on Jupiter are shallow, reaching only 10 to 20 kilometers below the visible cloud deck or “surface” of the planet, which has a radius of 70,000 km. Most of the colorful, swirling patterns in the bands that encircle the planet are shallow.

Some weather, however, emerges much deeper in the troposphere, redistributing ammonia and water and essentially unmixing what was long thought to be a uniform atmosphere. The three types of weather events responsible are hurricane-like vortices, hotspots coupled to ammonia-rich plumes that wrap around the planet in a wave-like structure, and large storms that generate mushballs and lightning.

“Every time you look at Jupiter, it’s mostly just surface level,” Moeckel said. “It’s shallow, but a few things — vortices and these big storms — can punch through.”

“Juno really shows that ammonia is depleted at all latitudes down to about 150 kilometers, which is really odd,” said de Pater, who discovered 10 years ago that ammonia was depleted down to about 50 km. “That’s what Chris is trying to explain with his storm systems going much deeper than we expected.”

Inferring planet composition from observations of clouds

Gas giants like Jupiter and Saturn and ice giants like Neptune and Uranus are a major focus of current space missions and large telescopes, including the James Webb Space Telescope, in part because they can help us understand the formation history of our solar system and ground truth observations of distant exoplanets, many of which are large and gaseous. Since astronomers can see only the upper atmospheres of faraway exoplanets, knowing how to interpret chemical signatures in these observations can help scientists infer details of exoplanet interiors, even for Earth-like planets.

“We’re basically showing that the top of the atmosphere is actually a pretty bad representative of what is inside the planet,” Moeckel said.

That’s because storms like those that create mushballs unmix the atmosphere so that the chemical composition of the cloud tops does not necessarily reflect the composition deeper in the atmosphere. Jupiter is unlikely to be unique.

“You can just extend that to Uranus, Neptune — certainly to exoplanets as well,” de Pater said.

The atmosphere on Jupiter is radically different from that on Earth. It’s primarily made of hydrogen and helium gas with trace amounts of gaseous molecules, like ammonia and water, which are heavier than the bulk atmosphere. Earth’s atmosphere is mainly nitrogen and oxygen. Jupiter also has storms, like the Great Red Spot, that last for centuries. And while ammonia gas and water vapor rise, freeze into droplets, like snow, and rain down continually, there is no solid surface to hit. At what point do the raindrops stop falling?

“On Earth, you have a surface, and rain will eventually hit this surface,” Moeckel said. “The question is: What happens if you take the surface away? How far do the raindrops fall into the planet? This is what we have on the giant planets.”

That question has piqued the interest of planetary scientists for decades, because processes like rain and storms are thought to be the main vertical mixers of planetary atmospheres. For decades, the simple assumption of a well-mixed atmosphere guided inferences about the interior makeup of gas giant planets like Jupiter.

Observations by radio telescopes, much of it conducted by de Pater and colleagues, show that this simple assumption is false.

“The turbulent cloud tops would lead you to believe that the atmosphere is well mixed,” said Moeckel, invoking the analogy of a boiling pot of water. “If you look at the top, you see it boiling, and you would assume that the whole pot is boiling. But these findings show that even though the top looks like it’s boiling, below is a layer that really is very steady and sluggish.”

The microphysics of mushballs

On Jupiter, the majority of water rain and ammonia snow appears to cycle high up in the cold atmosphere and evaporate as it falls, Moeckel said. Yet, even before Juno’s arrival at Jupiter, de Pater and her colleagues reported an upper atmosphere lacking in ammonia. They were able to explain these observations, however, through dynamic and standard weather modeling, which predicted a rainout of ammonia in thunderstorms down to the water layer, where water vapor condenses into a liquid.

But radio observations by Juno traced the regions of poor mixing to much greater depths, down to about 150 km, with many areas puzzlingly depleted of ammonia and no known mechanism that could explain the observations. This led to proposals that water and ammonia ice must form hailstones that fall out of the atmosphere and remove the ammonia. But it was a mystery how hailstones could form that were heavy enough to fall hundreds of kilometers into the atmosphere.

To explain why ammonia is missing from parts of Jupiter’s atmosphere, planetary scientist Tristan Guillot proposed a theory involving violent storms and slushy hailstones called mushballs. In this idea, strong updrafts during storms can lift tiny ice particles high above the clouds — more than 60 kilometers up. At those altitudes, the ice mixes with ammonia vapor, which acts like antifreeze and melts the ice into a slushy liquid. As the particles continue to rise and fall, they grow larger — like hailstones on Earth — eventually becoming mushballs the size of softballs.

These mushballs can trap large amounts of water and ammonia with a 3 to 1 ratio. Because of their size and weight, they fall deep into the atmosphere — well below where the storm started — carrying the ammonia with them. This helps explain why ammonia appears to be missing from the upper atmosphere: it’s being dragged down and hidden deep inside the planet, where it leaves faint signatures to be observed with radio telescopes.

However, the process depends on a number of specific conditions. The storms need to have very strong updrafts, around 100 meters per second, and the slushy particles must quickly mix with ammonia and grow large enough to survive the fall.

“The mushball journey essentially starts about 50 to 60 kilometers below the cloud deck as water droplets. The water droplets get rapidly lofted all the way to the top of the cloud deck, where they freeze out and then fall over a hundred kilometers into the planet, where they start to evaporate and deposit material down there,” Moeckel said. “And so you have, essentially, this weird system that gets triggered far below the cloud deck, goes all the way to the top of the atmosphere and then sinks deep into the planet.”

Unique signatures in the Juno radio data for one storm cloud convinced him and his colleagues that this is, indeed, what happens.

“There was a small spot under the cloud that either looked like cooling, that is, melting ice, or an ammonia enhancement, that is, melting and release of ammonia,” Moeckel said. “It was the fact that either explanation was only possible with mushballs that eventually convinced me.”

The radio signature could not have been caused by water raindrops or ammonia snow, according to paper co-author Huazhi Ge, an expert in cloud dynamics on giant planets and a postdoctoral fellow at the California Institute of Technology in Pasadena.

“The Science Advances paper shows, observationally, that this process apparently is true, against my best desire to find a simpler answer,” Moeckel said.

Coordinated observations of Jupiter

Scientists around the world observe Jupiter regularly with ground-based telescopes, timed to coincide with Juno’s closest approach to the planet every six weeks. In February 2017 and April 2019 — the periods covered by the two papers — the researchers used data from both the Hubble Space Telescope (HST) and the Very Large Array (VLA) in New Mexico to complement Juno observations in an attempt to create a 3D picture of the troposphere. The HST, at visible wavelengths, provided measurements of reflected light off the cloud tops, while the VLA, a radio telescope, probed tens of kilometers below the clouds to provide global context. Juno’s Microwave Radiometer explored the deep atmosphere of Jupiter over a limited region of the atmosphere.

“I essentially developed a tomography method that takes the radio observations and turns them into a three-dimensional rendering of that part of the atmosphere that is seen by Juno,” Moeckel said.

The 3D picture of that one swath of Jupiter confirmed that most of the weather is happening in the upper 10 kilometers.

“The water condensation layer plays a crucial role in controlling the dynamics and the weather on Jupiter,” Moeckel said. “Only the most powerful storms and waves can break through that layer.

Moeckel noted that his analysis of Jupiter’s atmosphere was delayed by the lack of publicly available calibrated data products from the Juno mission. Given the current level of data released, he was forced to independently reconstruct the mission team’s data processing methods — tools, data and discussions that, if shared earlier, could have significantly accelerated independent research and broadened scientific participation. He has since made these resources publicly available to support future research efforts.

The work was funded in part by a Solar System Observations (SSO) award from NASA (80NSSC18K1003).