“While it has been recognized that shallowing groundwater will eventually result in chronic flooding as it surfaces, what’s less known is that it can start causing problems decades beforehand as groundwater interacts with buried infrastructure,” said Shellie Habel, lead author and coastal geologist in the School of Ocean and Earth Science and Technology (SOEST) at UH Manoa. “This knowledge gap often results in coastal groundwater changes being fully overlooked in infrastructure planning.”

The research team aimed to create awareness about these issues and offer guidance from world experts on managing them. Habel and co-authors reviewed existing literature to examine the diverse effects on different types of infrastructure. Additionally, by employing worldwide elevation data and geospatial data that indicate the extent of urban development, they identified 1,546 low-lying coastal cities and towns globally, where around 1.42 billion people live, that are likely experiencing these impacts.

“The IPCC 6th Assessment Report tells us that sea level rise is an unstoppable and irreversible reality for centuries to millennia,” said Chip Fletcher, study co-author, interim Dean of SOEST, and director of the Climate Resilience Collaborative (CRC) at UH Manoa. “Now is the time to prepare for the challenges posed by this problem by redesigning our communities for greater resilience and social equity.”

Concealed damage

Well before the visible effects of surface flooding, sea-level rise pushes up the water table and shifts salty water landward. With this, the subsurface environment becomes more corrosive to critical underground infrastructure networks — buried drainage and sewage lines can become compromised and mobilize urban contamination, and building foundations can weaken.

Extensive research conducted by the CRC has substantiated that critical infrastructure around the world, including drainage and basements, is likely currently experiencing flooding from rising groundwater levels.

“The damage caused by sea level rise-influenced coastal groundwater is often concealed and not immediately perceptible,” said Habel, who is based at the CRC and Hawai’i Sea Grant in SOEST. “As a result, it tends to be overlooked in infrastructure management and planning efforts.”

Informing management strategies

The study authors emphasize the importance of research efforts that can contribute to informed adaptation strategies.

“Being aware of these hidden impacts of sea level rise is of significant importance for the State of Hawai’i due to the concentration of communities situated along low-lying coastal zones where groundwater is generally very shallow,” said Habel.

The CRC actively collaborates with partners across the nation and infrastructure managers in Hawai’i to gain a comprehensive assessment of how vital infrastructure, encompassing pipe networks, roadways, and buildings, is impacted. Understanding the impacts and risks associated with sea level rise-influenced coastal groundwater enables more effective management and adaptation.

Ever since the cameras of NASA’s New Horizons mission discovered a large heart-shaped structure on the surface of the dwarf planet Pluto in 2015, this “heart” has puzzled scientists because of its unique shape, geological composition, and elevation. A team of scientists from the University of Bern, including several members of the NCCR PlanetS, and the University of Arizona in Tucson have used numerical simulations to investigate the origins of Sputnik Planitia, the western teardrop-shaped part of Pluto’s “heart” surface feature. According to their research, Pluto’s early history was marked by a cataclysmic event that formed Sputnik Planitia: a collision with a planetary body about 700 km in diameter, roughly twice the size of Switzerland from east to west. The team’s findings, which were recently published in Nature Astronomy, also suggest that the inner structure of Pluto is different from what was previously assumed, indicating that there is no subsurface ocean.

A divided heart

The “heart,” also known as the Tombaugh Regio, captured the public’s attention immediately upon its discovery. But it also immediately caught the interest of scientists because it is covered in a high-albedo material that reflects more light than its surroundings, creating its whiter color. However, the “heart” is not composed of a single element. Sputnik Planitia (the western part) covers an area of 1200 by 2000 kilometers, which is equivalent to a quarter of Europe or the United States. What is striking, however, is that this region is three to four kilometers lower in elevation than most of Pluto’s surface. “The bright appearance of Sputnik Planitia is due to it being predominantly filled with white nitrogen ice that moves and convects to constantly smooth out the surface. This nitrogen most likely accumulated quickly after the impact due to the lower altitude,” explains Dr. Harry Ballantyne from the University of Bern, lead author of the study. The eastern part of the “heart” is also covered by a similar but much thinner layer of nitrogen ice, the origin of which is still unclear to scientists, but is probably related to Sputnik Planitia.

An oblique impact

“The elongated shape of Sputnik Planitia strongly suggests that the impact was not a direct head-on collision but rather an oblique one,” points out Dr. Martin Jutzi of the University of Bern, who initiated the study. So the team, like several others around the world, used their Smoothed Particle Hydrodynamics (SPH) simulation software to digitally recreate such impacts, varying both the composition of Pluto and its impactor, as well as the velocity and angle of the impactor. These simulations confirmed the scientists’ suspicions about the oblique angle of impact and determined the composition of the impactor.

“Pluto’s core is so cold that the rocks remained very hard and did not melt despite the heat of the impact, and thanks to the angle of impact and the low velocity, the core of the impactor did not sink into Pluto’s core, but remained intact as a splat on it,” explains Harry Ballantyne. “Somewhere beneath Sputnik is the remnant core of another massive body, that Pluto never quite digested,” adds co-author Erik Asphaug from the University of Arizona. This core strength and relatively low velocity were key to the success of these simulations: lower strength would result in a very symmetrical leftover surface feature that does not look like the teardrop shape observed by New Horizons. “We are used to thinking of planetary collisions as incredibly intense events where you can ignore the details except for things like energy, momentum and density. But in the distant Solar System, velocities are so much slower, and solid ice is strong, so you have to be much more precise in your calculations. That’s where the fun starts,” says Erik Asphaug. The two teams have a long record of collaborations together, exploring since 2011 already the idea of planetary “splats” to explain, for instance, features on the far side of the Moon. After our moon and Pluto, the University of Bern team plans to explore similar scenarios for other outer Solar System bodies such as the Pluto-like dwarf planet Haumea.

No subsurface ocean on Pluto

The current study sheds new light on Pluto’s internal structure as well. In fact, a giant impact like the one simulated is much more likely to have occurred very early in Pluto’s history. However, this poses a problem: a giant depression like Sputnik Planitia is expected to slowly move towards the pole of the dwarf planet over time due to the laws of physics, since it has a mass deficit. Yet it is paradoxically near the equator. The previous theorized explanation was that Pluto, like several other planetary bodies in the outer Solar System, has a subsurface liquid water ocean. According to this previous explanation, Pluto’s icy crust would be thinner in the Sputnik Planitia region, causing the ocean to bulge there, and since liquid water is denser than ice, you would end up with a mass surplus that induces migration toward the equator.

However, the new study offers an alternative perspective. “In our simulations, all of Pluto’s primordial mantle is excavated by the impact, and as the impactor’s core material splats onto Pluto’s core, it creates a local mass excess that can explain the migration toward the equator without a subsurface ocean, or at most a very thin one,” explains Martin Jutzi. Dr. Adeene Denton from the University of Arizona, also co-author of the study, is currently conducting a new research project to estimate the speed of this migration. “This novel and inventine origin for Pluto’s heart-shaped feature may lead to a better understanding of Pluto’s origin,” she concludes.

But what happens once those particles are inside? What do they do to our digestive system?

In a recent paper published in the journal Environmental Health Perspectives, University of New Mexico researchers found that those tiny particles — microplastics — are having a significant impact on our digestive pathways, making their way from the gut and into the tissues of the kidney, liver and brain.

Eliseo Castillo, PhD, an associate professor in the Division of Gastroenterology & Hepatology in the UNM School of Medicine’s Department of Internal Medicine and an expert in mucosal immunology, is leading the charge at UNM on microplastic research.

“Over the past few decades, microplastics have been found in the ocean, in animals and plants, in tap water and bottled water,” Castillo, says. “They appear to be everywhere.”

Scientists estimate that people ingest 5 grams of microplastic particles each week on average — equivalent to the weight of a credit card.

While other researchers are helping to identify and quantify ingested microplastics, Castillo and his team focus on what the microplastics are doing inside the body, specifically to the gastrointestinal (GI) tract and to the gut immune system.

Over a four-week period, Castillo, postdoctoral fellow Marcus Garcia, PharmD, and other UNM researchers exposed mice to microplastics in their drinking water. The amount was equivalent to the quantity of microplastics humans are believed to ingest each week.

Microplastics had migrated out of the gut into the tissues of the liver, kidney and even the brain, the team found. The study also showed the microplastics changed metabolic pathways in the affected tissues.

“We could detect microplastics in certain tissues after the exposure,” Castillo says. “That tells us it can cross the intestinal barrier and infiltrate into other tissues.”

Castillo says he’s also concerned about the accumulation of the plastic particles in the human body. “These mice were exposed for four weeks,” he says. “Now, think about how that equates to humans, if we’re exposed from birth to old age.”

The healthy laboratory animals used in this study showed changes after brief microplastic exposure, Castillo says. “Now imagine if someone has an underlying condition, and these changes occur, could microplastic exposure exacerbate an underlying condition?”

He has previously found that microplastics are also impacting macrophages — the immune cells that work to protect the body from foreign particles.

In a paper published in the journal Cell Biology & Toxicology in 2021, Castillo and other UNM researchers found that when macrophages encountered and ingested microplastics, their function was altered and they released inflammatory molecules.

“It is changing the metabolism of the cells, which can alter inflammatory responses,” Castillo says. “During intestinal inflammation — states of chronic illness such as ulcerative colitis and Crohn’s disease, which are both forms of inflammatory bowel disease — these macrophages become more inflammatory and they’re more abundant in the gut.”

The next phase of Castillo’s research, which is being led by postdoctoral fellow Sumira Phatak, PhD, will explore how diet is involved in microplastic uptake.

“Everyone’s diet is different,” he says. “So, what we’re going to do is give these laboratory animals a high-cholesterol/high-fat diet, or high-fiber diet, and they will be either exposed or not exposed to microplastics. The goal is to try to understand if diet affects the uptake of microplastics into our body.”

Castillo says one of his PhD students, Aaron Romero, is also working to understand why there is a change in the gut microbiota. “Multiple groups have shown microplastics change the microbiota, but how it changes the microbiota hasn’t been addressed.”

Castillo hopes that his research will help uncover the potential impacts microplastics are having to human health and that it will help spur changes to how society produces and filtrates plastics.

“At the end of the day, the research we are trying to do aims to find out how this is impacting gut health,” he says. “Research continues to show the importance of gut health. If you don’t have a healthy gut, it affects the brain, it affects the liver and so many other tissues. So even imagining that the microplastics are doing something in the in the gut, that chronic exposure could lead to systemic effects.”