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Ask a Scientist

Fighting Big Ag Pollution with Maps and Math

When I was living in Cleveland in 1969, the shores of Lake Erie were littered with dead fish and an oil slick on the Cuyahoga River, which snakes through the center of town, famously caught on fire. The main cause? Industrial pollution. For decades, the steel mills and other factories that lined the river had been spewing toxins into the air and dumping raw, untreated chemicals into the water, which emptied into the lake. I distinctly remember the rotten egg smell hanging over the Flats whenever we went downtown.

The Cuyahoga fire, along with a major oil spill off the coast of Santa Barbara that same year, galvanized national attention and led to the first Earth Day, a slew of new air and water protection laws, and the creation of new federal departments to administer them, including the Environmental Protection Agency (EPA).

Today, our air and water are significantly cleaner than they were 50 years ago thanks to the Clean Air Act, the Clean Water Act, and other environmental safeguards Congress passed back then. But those laws primarily focused on the industrial sector, leaving agriculture largely alone. That was—and still is—a major oversight.

Big Ag is a major polluter. According to the EPA, it applies about a half million tons of pesticides, 12 million tons of nitrogen, and 4 million tons of phosphorus fertilizer to crops in the continental United States every year. Runoff from these applications, as well as from soil erosion and livestock manure, is the leading cause of river and stream pollution, the second leading cause of wetland pollution, and the third leading cause of lake pollution. Regardless, only 30 percent of the nation’s biggest livestock farms, known as concentrated animal feeding operations (CAFOs), have waste discharge permits.

In the case of Lake Erie, the industrial pollution of 50 years ago has been largely replaced by runoff pollution from fields in the Maumee River watershed. That runoff, mainly from fertilizer, creates a toxic algal bloom in the lake every summer, threatening the drinking water supply of millions of people as well as the habitat of fish and other aquatic life. There’s an even bigger low-oxygen “dead zone” that forms every summer in the Gulf of Mexico off the coast of Texas and Louisiana. Triggered by nitrogen-rich fertilizer runoff from vast swaths of monoculture fields and large-scale livestock operations across the Midwest, it covered about 3,000 square miles earlier this year.

The Union of Concerned Scientists (UCS) has been ringing the alarm bell about agricultural pollution for years. Fifteen years ago, the Food and Environment Program published a 94-page report, CAFOs Uncovered: The Untold Costs of Confined Animal Feeding Operations. And just three years ago, Reviving the Dead Zone provided the first comprehensive assessment of the Gulf of Mexico dead zone’s economic impact, and warned the root problem—agricultural runoff pollution—will likely worsen due to climate change.

Now the Food and Environment Program is incorporating a new approach to these and other related issues courtesy of the newest addition to its staff, geostatistician Stacy Woods, who became the program’s research director in February. Woods, who previously worked at the EPA and the Natural Resources Defense Council (NRDC), holds a doctorate degree in environmental health engineering and a master’s degree in public health from Johns Hopkins University. I recently sat down with her virtually to ask her about her background and how she plans to apply her skills and experience to addressing agricultural pollution and other program agenda items.

EN: First, welcome to UCS. I’m sure a lot of our readers are as curious as I am about just what you do and how it applies to the work our Food and Environment Program is doing. Geostatistics has a lot of applications, no?

SW: Geostatistics is a way to understand spatially related data, where things that are closer together tend to be more similar than things that are farther apart. Geostatistics can be applied to any spatially dependent data, and it is commonly used in environmental science investigations.

If a factory is dumping chemicals into a river and you take a water sample from the river near that factory, you would expect the water sample to be contaminated with the same chemicals the factory is expelling because the sample site and the polluting factory are located close to each other. While geostatistics involves very complex math, illustrating spatial data and analytical findings on a map can help communicate the science by rooting the information in a personal sense of place, like showing how a factory-polluted river empties into a lake where people swim, boat, and fish.

As a spatial statistician working on environmental policy, I use math to make sense of our environment and draw maps to communicate my research findings to policymakers and the general public. When I coauthored a 2018 peer-reviewed study in Science, for instance, I predicted where a particularly hazardous pesticide called chlorpyrifos could pollute waterways that manatees use to migrate in Florida. Chlorpyrifos is an organophosphate pesticide that the US government banned for use on food crops after we published our study, though it is still used in other parts of the world. It is especially toxic to manatees and other sea mammals because they lack a key enzyme that helps detoxify the chemical in their bloodstream.

While our original paper was published in a scientific journal, I used the map from the study to illustrate the problem for a wider audience and supported a successful campaign to ban chlorpyrifos. The map helped contextualize the scientific information, allowing blog readers and policymakers to see how a toxic chemical applied to agricultural fields threatened manatees—which were already facing extinction—in Florida’s waterways.

EN: You played a role in a 2018 lawsuit against the city of Flint, Michigan, over lead in its drinking water supply. City and state officials were notoriously negligent.

SW: To save money, Flint changed its water source and treatment protocols and—as a result—unleashed toxic lead from old water pipes into the municipal drinking water supply. When community members found out that their drinking water had dangerously high levels of lead, they sued the city of Flint and the state of Michigan.

I got involved after the city filed reports and maps to support its claim that it was fulfilling the requirements of a historic 2017 settlement to find and replace Flint’s lead pipes. After reviewing the city’s math and maps, I concluded that its estimate for the number of remaining lead pipes was not statistically sound, and filed an expert opinion to support the Flint community’s case.

I also testified on my analytical methods in federal court. That was a new experience for me! While I had previously taught spatial statistics to graduate students, in the Flint case, I found myself on the witness stand explaining these complex concepts to the court. I relied on simplified hypothetical examples—and a good number of emphatic hand gestures—to illustrate the intricate statistical theories and ample evidence that supported my estimates for the number of lead pipes that likely remained in Flint at the time of the trial.

Flint community members, represented by an exceptional NRDC litigation team, asked the court to compel the city to do a better job of finding and replacing lead pipes. The court sided with the community and ordered the city to use an analytically sound model developed by Eric Schwartz of the University of Michigan and Jacob Abernethy of the Georgia Institute of Technology to efficiently locate and replace the pipes. After the settlement, I partnered with Schwartz and Abernethy to create the Flint Service Line Map to share their model’s results with Flint residents so that they could take steps to protect themselves if their homes were likely serviced by a toxic lead water pipe.

EN: How did your experience in the Flint case influence your career and perspective?

SW: Working in Flint showed me how I could apply my research and spatial data science skills to support advocates working to secure safe, clean water for all. After that case, I continued to work on the issue, joining a campaign that compelled Newark, New Jersey, to reduce its residents’ exposure to lead by providing them with free water filters and replacing their lead pipes.

But I would say that the biggest impact that Flint had on me is that I witnessed firsthand the transformative power of community-led environmental advocacy. The people of Flint demanded that their government recognize their human right to clean and safe drinking water, and they won. And the community-driven advocacy in Flint and Newark are just two examples of people across the country demanding an end to our toxic legacy of lead water pipes. This nationwide collective action paved the way for the EPA’s recently announced groundbreaking plan to remove 10 million lead water service lines across the country within the next 10 years.

EN: Before we get to the issue of agriculture sector pollution, I wanted to ask you about the recent US Supreme Court decision that severely curtailed the EPA’s authority to protect millions of acres of wetlands. That ruling will certainly complicate efforts to protect US waterways. You got involved in a “waters of the United States” (WOTUS) case against the Trump administration EPA in 2020 that predated the Supreme Court ruling.

SW: In 2020, the Trump administration narrowed the scope of the Clean Water Act by stripping protections from streams and wetlands. I joined a lawsuit brought by people whose drinking water and community waterways were threatened by these changes. In that case, I used math to estimate the new rule’s devastating impacts and drew maps to show which communities’ waters would suffer more industrial and agricultural pollution.

In 2021, a US district court vacated the Trump rule, but the fight against clean water continued. One case, brought by Michael and Chantell Sackett of Idaho, made it all the way to the US Supreme Court, where it garnered support from large agriculture corporations and other polluting companies, states, and even members of Congress who jumped at the chance to weaken the laws that prevent water pollution. In a tremendous loss for everyone who depends on clean water—that is, all of us—the Supreme Court sided with the Sacketts and seriously undermined the Clean Water Act by stripping protections from countless wetlands. But the impact of this disastrous decision threatens more than just wetlands. It also provides a foundation for additional challenges to the laws that help protect our water, land, and communities.

EN: I mentioned a 2020 UCS report in my introduction that estimated that that nitrogen fertilizer runoff into the Gulf of Mexico has caused as much as $2.4 billion in damages annually to gulf fisheries and marine habitat since 1980. Your program recently published a fact sheet on nitrogen fertilizer, which most people do not know is manufactured using fossil gas—what the industry euphemistically calls “natural” gas because it sounds like a good thing when it is decidedly not. It is mainly methane, which is 80 times more potent than carbon dioxide in trapping heat for the first 20 years after it is released. That makes the fertilizer industry a double threat to the climate.

SW: Fertilizer companies encourage the industrial agriculture sector to overapply its product, and when all of that synthetic nitrogen-based fertilizer is sprayed on soil, nitrous oxide is emitted into the atmosphere. Nitrous oxide has been called the “forgotten greenhouse gas” because while it is a powerful contributor to climate change, it generates far fewer headlines than carbon dioxide. But nitrous oxide is even more insidiously efficient at disrupting the climate. A molecule of nitrous oxide is nearly 300 times more potent at trapping heat than a molecule of carbon dioxide!

Big Ag is releasing this powerful heat-trapping gas in ever larger amounts because of its growing reliance on synthetic fertilizer. In fact, a 2020 study found that nitrous oxide from human activities—mainly from applying nitrogen fertilizer to crops—jumped 30 percent over the past four decades. Unfortunately, once nitrous oxide is released into the air, it sticks around for more than 100 years before beginning to break down, heating the atmosphere and depleting the ozone layer.

Then there’s the fact that, before all of that synthetic fertilizer overloads agricultural fields, it is produced by fossil fuel-powered factories that emit methane and carbon dioxide. So from the factory to the field, the fertilizer industry delivers a multipronged hit to the environment, releasing dangerous heat-trapping gases at every step.  

EN: How do you plan to apply your maps and math methodology to your program’s work to help create a food and farm system that is more sustainable, resilient, healthy, and equitable?

SW: As you pointed out in your introduction, agriculture is a leading cause of water pollution in the United States thanks in large part to fertilizers, pesticides, and other pollutants from agricultural fields and factories. I’m excited to be using my background in geostatistics to investigate how our corporate-dominated industrial food and farming system contaminates our water, and to identify policy solutions to this critical problem.

But Big Ag pollutes more than water. From toxic air pollution to climate-changing emissions, large corporate agribusinesses threaten public health and the environment. And that pollution has compounding consequences. As agricultural emissions alter the climate, for example, the resulting warmer winters and waters exacerbate the risk agricultural chemicals pose to the nation’s waterways.   

Industrial agriculture and other polluting industries are fighting to weaken the laws that protect our water, air, and environment. I will continue to fight back with math and maps, using spatial data and geostatistics to assess environmental stressors, identify impacted areas, illustrate environmental damage, spotlight corporate bad actors, and push for policy solutions that safeguard our environment and our health. My experiences in Flint and beyond have shown me how we can use science and data to support advocacy, improve policy, and create a healthier environment for all.


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