Health and Our Oceans

2130th Stated Meeting | October 24, 2024 | University of California, San Diego
 

On October 24, 2024, the Academy’s San Diego Committee hosted a program on “Health and Our Oceans,” which featured atmospheric chemist and Academy member Kimberly A. Prather. Professor Prather discussed newly identified critical connections between rising pollution levels in coastal oceans and rivers and their far-reaching impacts on air quality and human health. She also described a recent study on local air and water quality issues in southern San Diego. The program included introductory remarks from Susan Taylor, Distinguished Professor of Pharmacology, Chemistry & Biochemistry at UC San Diego School of Medicine, and Margaret S. Leinen, Director of Scripps Institution of Oceanography, Vice Chancellor for Marine Sciences, and Dean of the School of Marine Sciences at UC San Diego. An edited version of Professor Prather’s presentation follows.

Kimberly A. Prather

Kimberly A. Prather is Distinguished Professor at the Scripps Institution of Oceanography with a joint appointment as the Distinguished Chair in Atmospheric Chemistry in the Department of Chemistry and Biochemistry at UC San Diego. She is the founding Director of the NSF Center for Aerosol Impacts on Chemistry of the Environment and Co-Director of the Meta-Institute for Airborne Disease in a Changing Climate. She was elected to the American Academy of Arts and Sciences in 2010.
 

Good evening and thank you for inviting me to be a part of this program. One of my favorite topics is aerosols. But for a long time many people didn’t understand what aerosols were. One outcome of the COVID-19 pandemic is that people began to recognize that aerosols are more than the stuff that comes out of a spray can. I had the honor of convincing Dr. Anthony Fauci that COVID is airborne, but not as droplets that fall to the ground, as was the understanding for about one hundred years.

Aerosols can travel all the way around the world in about two weeks (Slide 1). They seed our clouds. They have an impact on the location and amount of precipitation. The two most abundant and natural types of aerosols are dust and sea spray. We don’t fully understand how they interact with clouds, and this represents the single largest uncertainty in our understanding of climate change. Which aerosols seed clouds, and how effectively do they do that? We know they can change the brightness of clouds and the amount of light that gets reflected back to space and does not warm our planet. And they can change whether the clouds produce rain or snow, and how much they produce.
 

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When I moved to Scripps Institution of Oceanography, I ramped up my efforts on the climate change aspects of aerosols, and that’s what I have been doing for quite a while. I directed a Center for Chemical Innovation. The center, funded by the National Science Foundation, started in 2010 and has run for fourteen years. We have an incredible team and they have taught me the importance of interdisciplinary work. The center allowed us to work with oceanographers, microbiologists, and data scientists. Since it was a chemistry-funded center, we always kept our sights on the chemistry part. We were solving a big problem and that problem was related to aerosol chemistry and the impact on climate.

I have done studies for twenty years out in the field, and early in my career I developed an instrument that we flew through clouds. We used the instrument in ships and planes all over the world. I never felt completely satisfied at understanding what the oceans were doing to our planet, as they represent 71 percent of the earth’s surface. So that’s an important gap in our understanding. But oceans are hard to study because they are so vast.

So what we proposed to the National Science Foundation (NSF) was to move the ocean, atmosphere, waves, and winds into the lab, and we were fortunate to do that here at Scripps. We created the NSF Center for Aerosol Impacts on Chemistry of the Environment (CAICE) with the following mission: “To transform our ability to accurately predict the impact of aerosols on climate and our environment by bringing the full real-world chemical complexity of the ocean-atmosphere into the laboratory.”

We started with one question: What is the spray that comes out of the ocean? Most people think it’s sodium chloride because that’s mostly what the ocean is, right? Not exactly. The ocean is composed of hundreds of millions of different compounds: phytoplankton, proteins, lipids, viruses, etc. The ocean produces over half of the air that we breathe (Slide 2). It’s like a forest living underwater. So how do we move the ocean-atmosphere system into the lab, and how do we make sure that sea spray aerosols look just like they do when produced from the ocean?
 

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This type of work had not been done before. We needed people working across disciplines to make it happen. And we did exactly that at Scripps in what’s called the SIO Hydraulics Laboratory. In Slide 3, you can see the long wave channel, and we pump seawater directly into it from the ocean—about 3,600 gallons of seawater. We took something that people had been using to study the ocean and we put a lid on it. Then we cleaned all the air above so that when things came out of the ocean, we could see them. They wouldn’t react away, they wouldn’t disappear, they wouldn’t change to something else. This allowed us to explore what comes out of the ocean, how much comes out of the ocean, and what controls the quantity that comes out of the ocean. We wondered how biology was involved. What happens when you induce a phytoplankton bloom?
 

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This was a proof of concept and the work we did in the first three years during the exploratory phase earned us ten more years of funding. Leading something of this magnitude with a magical team that came together to do this work really changed my career.

We moved from having one channel with 3,600 gallons of seawater to a massive system called SOARS—Scripps Ocean-Atmosphere Simulator—that has wind and waves in 36,000 gallons of seawater. We can control the air and water temperature. We can even make sea ice. Its newest feature allows us to create hurricane force winds—105 miles/hour was the number that I heard last. In addition, the atmospheric reaction chamber is allowing us to begin to understand this synergy between the ocean and the atmosphere. We have light pipes that come in through the roof so we can induce blooms. We can study different conditions and different microbes. For decades people didn’t know how much sea spray came out of the ocean with a breaking wave or with a certain wind speed or at a certain ocean temperature. But our team found those answers and they are incredibly reproducible. This work is much easier to do in SOARS than it is in the real world because in the real world your measurements are always complicated by having input of pollution from humans.

In slide 4, we see a viewing room where we can watch the waves. We can image the bubbles, the waves, and the foam. We are trying to understand the physics and the biology of what is affecting the chemistry of the things that get into the air. We have acoustics equipment so we can listen to the bubbles pop. We can measure the size of the bubbles. Bubbles are everything to spray and to aerosolization.
 

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Let’s talk a little bit about aerosolization. In Slide 5, we are looking at breaking waves. The white part that we see is where all the bubbles are, where all the action is. We see film drops and jet drops. Because the surface is like oil and vinegar dressing, it forms a film, and when that ruptures that’s what leads to the spray. We spent three years working on this and we started to see all kinds of interesting things coming out of the ocean. We saw bacteria being invaded by phage. We saw little micelle structures that had never been seen before in the air.
 

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Why am I so excited about aerosolization from the ocean? At first, I was interested in its ability to affect clouds and climate, but then I started thinking about the health effects, which has largely been inspired by living here. We have a very polluted ocean. In Slide 6, we see one of the members of my group with air sampling instruments. The sewage crisis in San Diego doesn’t only affect you if you go in the water. Your main exposure is from the air that you are breathing. And nobody had really thought about that. Brace yourself. You may not like your Saturday morning walk on the beach as much after this talk. I apologize, but at least you’ll know when not to take that walk or where not to go.
 

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We inhale 11,000 liters of air each day, and so that is our number one exposure pathway, which has been almost completely ignored, especially the connection with what comes out of polluted water in the ocean. Counties in California have declared a local state of emergency and people are pushing to make it a federal state of emergency. As a scientist, I believe it truly is a federal state of emergency. I don’t know of another place in the United States where if you had a broken sewer pipe, with 80 million gallons of sewage running through your streets, that they would allow that to continue for decades.

We have been very involved in trying to make things better in southern San Diego. And I think we’re making some progress. The red dots in this map in Slide 7 represent beaches that are closed because of high bacteria levels in the water, and it is mostly the beaches in the southernmost communities that are closed.
 

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People have been complaining for a long time about not feeling well, but those reports are escalating. We are hearing many more stories about lung and heart issues and people not being able to sleep.

How did we get started on our work studying whether polluted coastal water impacts air quality? In 2017, Scripps oceanographers Sarah Giddings and Falk Feddersen conducted an experiment in which they put pink dye in the water to determine if dilution is the solution to pollution. Does the pollution, in this case the pink dye, go out to sea or does it get trapped in the surf zone? And if it does get trapped in the surf zone, how far up and down, how many beaches, and how many people are affected?

We were involved in that research. We looked for the pink dye in the air, and we detected it all across San Diego. This was our first indirect indicator that polluted coastal water was getting trapped in the surf zone where it was aerosolized. Most of our studies have been done in what we call our rainy season, when there is massive rain and intense storms. In 2023, there were 44 billion gallons of polluted water that ran through the Tijuana River and into the ocean. That was a record. This year we think it will be closer to 40 billion gallons of polluted water. Luckily some of that polluted water is diluted by precipitation.

We started to think about all the things in the water and what gets transferred into the air. When you go to a place that’s heavily polluted, you start to see in the water lots of things that are from humans, especially when there’s flooding from storms. Once those pollutants get into the air they can get transferred through weather and air patterns over many miles and long distances, affecting people who are exposed through inhalation to those coastal waterborne pollutants.

Many people felt that they were okay because they didn’t live here and didn’t go to a beach that had high bacteria levels in the water. But once we started showing that polluted coastal water impacts air quality all the way to La Jolla, then people started paying more attention.

One of our studies involved putting plates outside at Imperial Beach and at Scripps to see if there’s any growth from the airborne microbes in those locations (Slide 8). We didn’t see much on the plates at Scripps, while the ones at Imperial Beach had a lot of growth. Matthew Pendergraft was one of my Scripps students. He showed in a paper from 2023 that up to 76 percent of the bacteria in the air at Imperial Beach could be traced back to sewage in the Tijuana River.
 

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This finding was larger than any of us expected, and it led many people to start thinking about chemical pollutants. Sewage contains all kinds of industrial waste. The Tijuana River starts on the other side of the border, and the factories (Maquiladoras) there can dump things into the river that would be illegal for us to dump here (Slide 9). What we showed was that if the ocean concentration of things like antibiotics, cocaine, methamphetamine, and sunscreen, among thousands of other pollutants, is high, then the air concentration of those chemical pollutants is also high. There’s a direct correlation between polluted water and polluted air. This was a significant finding.
 

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So what have we been doing recently? Some of the students in my lab are studying air effects and others are involved in work on the biological side. I appreciate biology far more than I ever expected as I’ve developed a greater understanding of airborne microbes or bioaerosols. We are looking at DNA and RNA in the air. As we know from COVID, when people are sick, the virus can be detected in wastewater. But is it also in the air?

In 2023, we did a study about airborne microbes and transboundary water flow, meaning the flow in the Tijuana River that is coming across the border (Slide 10). One of the things we saw was that every time there was a rain event, we would see a spike in DNA in the air, indicated by the red circles in the chart. The data are hinting that most of the DNA that we are detecting in the air is coming from the river that’s surging across the border.
 

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If we look at RNA in the air, we see something similar: Both the DNA and the RNA in the air are amplified. The bacteria and viruses accumulate in the top sea surface microlayer. They can be enriched by a factor of up to 100,000 in the air relative to what they are in the water.

We set up different air filters at Imperial Beach. And we found phage-like particles in the samples—the first time intact airborne phage were detected in urban air samples. It is fairly common to see phage at wastewater treatment plants, but no one had ever detected it in urban air, perhaps because it is challenging to sample air. From a microbial perspective, air is hard to sample because of the harsh process that we use to collect it. We worked hard to keep things intact, and I’m pleased to say that we’re finally there. When you detect phage, that is one of the best indicators of a strong influence from wastewater.

We are starting to see evidence of more pollution coming across from transboundary flow, and that pollution has caused a lot of damage. Many of our studies in 2023 and 2024 were done in the wet season. But we also did a dry season study and started sampling in August 2024.

We wanted to see what was coming out of the ocean during the dry season when we expected the polluted water would be coming from Punta Bandera, which is about 10 kilometers south of the border. We expected most of the pollution in the ocean to be coming up from Mexico, but that’s not what we found.

We set up air quality instruments all across the region. We started at Imperial Beach. We talked to the residents and there were record numbers of odor reports, over two hundred per day. We tested in Nestor, a small community near the river. We wanted to know what was causing the terrible smell, the headaches, the respiratory issues, and the lack of sleep for the residents. When we went out in the field, we wore full-body suits and respirators because the air was so toxic it burned if you weren’t properly protected.

We set out to measure air quality, not (initially) to figure out what was causing this public health crisis. But when the community is hurting we jumped in to do what we could. The community was telling us, “It smells like a porta-potty (like rotten eggs) all the time.” Smell messes with your mental status. The community felt that they were being gaslit because they knew they didn’t feel well, but nobody would do anything. What’s interesting is that right before our study I asked my group to buy a hydrogen sulfide monitor. Don’t ask me why. We decided to measure hydrogen sulfide concentrations in Nestor where the community directed us.

Each night we found a spike in hydrogen sulfide concentrations. People were sealing the doors and windows of their houses with tape, trying to keep the toxic smell out. As awful as this situation was, the community finally felt heard. We were listening and collecting data to address the crisis.

A lot happened over a short span of time. On September 1, 2024, we started taking air measurements in Nestor. On September 2, 3, and 4, we recorded high H₂S concentrations at night. On September 5, I presented our initial results to the Imperial Beach Task Force, which includes scientists, doctors, and others from the area. We also invited people from the San Diego County Health and Human Services, and they were silent during the entire meeting. No comments, no questions. It was very odd.

Next, the mayor of Imperial Beach said we needed to have a press conference to warn the public. At this point, my San Diego State colleagues and I were dead tired, but I said okay. They started printing out our data. On September 9, we participated in a press conference at Imperial Beach and showed our early data that there were extremely high concentrations of H₂S in the air. The data validated the community’s concerns. What happened next was surprising. On September 10, they diverted the Tijuana River. A San Diego State colleague and I were on a call with Congress and Senate representatives trying to explain that we do know what we’re doing. We were constantly saying, “No, no, the data are correct.” And they said, “Well, the river flow just stopped.”

We rushed down to the river, and though there was still a trickle of water, it wasn’t millions of gallons of water! On September 11 and the days following, the H₂S levels and odors had decreased. On September 22, Imperial Beach opened for the first time in over one thousand days. We are writing up our results and are almost ready to submit them for publication. The Tijuana River flow went from more than 50 million gallons per day of raw unprocessed wastewater to less than 3 million gallons flowing through the Tijuana River Valley.

There was a direct correlation between the community odor reports and the H₂S concentrations in Nestor. The residents were the canaries in the coal mine and no one was listening to them. They didn’t need our expensive instruments. If they had just listened to the community, the public health crisis could have been averted.

Let me summarize what we found.

• Poor air quality impacts many more residents than just those visiting the beach. Air quality models show air pollutants traveling for miles.
• The Tijuana River remains diverted for now, though the rainy season is coming and we don’t know what will happen then.
• Nightly releases of water starting at 6:00 pm and ending at 6:00 am are leading to increased flow.
• H₂S levels are lower, but remain well above acceptable standards.
• Beaches were open for the first time in over one thousand days, but they are now closed again.
• San Diego State University and the CDC have launched health surveys for residents living and working in the region.
• Efforts are underway to get air purifiers into homes near hotspots.
• The San Diego Air Pollution Control District is increasing air monitoring efforts in the region.
• Multiple requests for a state of emergency have been sent to President Biden. Those requests include our data, so that’s why we need our data peer reviewed and published as soon as we can.
• At last count, three major lawsuits have been launched.
• More results are coming. We are continuing to collect and analyze groundwater, soil, and aerosol samples.
• We are doing more community health surveys, collecting indoor dust samples, and conducting indoor and outdoor air sampling.

None of this work would have been possible without Cindy Dankberg. She and her family supported our research program. I want to thank the entire Dankberg family for their support. My presentation tonight is dedicated to Cindy’s memory. I also want to thank the amazing team of researchers in my group.

Q&A Session
 

AUDIENCE MEMBER: I am curious if you have any idea how these aerosols affect biological systems. Have you tried to recapitulate them and put them on cell cultures to see if there’s a change in epigenetics? Do you have longitudinal studies of these populations? Can you see any direct impacts?

PRATHER: We’re trying to figure that out right now, and I’d love to hear ideas of how to get a handle on what happens when you inhale this cocktail. We’re working with one of my colleagues who is exposing lung organoids to our air samples. Let’s just say they don’t last very long. We have so many questions, and we have a pretty steep hill to climb. One piece of good news is that UCSD Health is taking a mobile clinic to south San Diego and we should start to see data that help us connect and understand the human and health aspects. We are still doing health surveys to collect really important data. But we have a lot more work to do.

AUDIENCE MEMBER: Do the marine layer and fog have any effect? Have complaints increased or decreased during times when there is fog?

PRATHER: Temperature is a big driver. H₂S is heavier than air so temperature traps it and holds it down near the ground. Another factor are the winds that die at night. And then there’s river flow and turbulence. Regarding your question about fog, many of the residents were very sick during a period when we had heavy fog, and the levels weren’t that high. What we think was happening is that fog is like a sponge for acidic gases. If you have a weakened respiratory and pulmonary system and there’s heavy fog, it makes things much worse.

AUDIENCE MEMBER: I have a simple question and then one that may not be so simple. First, how do you turn off a whole river?

PRATHER: You divert it.

AUDIENCE MEMBER: Who diverted it?

PRATHER: Someone in Mexico.

AUDIENCE MEMBER: My second question is, if you didn’t have the personal witness of the residents, would you have eventually reached the same conclusion from the public health statistics?

PRATHER: It certainly would have been harder because the residents led us to that spot. They were our best sensors, and sadly for a long time they were dismissed. But not anymore.

AUDIENCE MEMBER: I’m fascinated about the possibilities for sampling aerosols. What is the state of the art in autonomous underwater vehicles, surface vehicles, and drones? Is sampling happening at more sites?

PRATHER: I was working with someone recently from Virginia Tech who is one of the leaders in using drones. We are using smaller samplers, and there’s a debate of whether you put the samples on a filter or into liquid. I like the liquid, because it seems less harsh. But we are still working through that. The instruments are now small enough that you can fly them on drones. The drones let us swoop into places where it is not safe for people to go. The drones were able to get samples of the foam that we would not have been able to get.

Thank you everyone.

© 2025 by Kimberly A. Prather

To view or listen to the presentation, visit the Academy’s website.