Unearthing Lead: Solving the Mystery Behind Pollution Maps
In 2017, Yvette Cabrera walked the streets of Santa Ana with a portable XRF machine, a device used for measuring heavy metals in the soil. Cabrera, an investigative reporter researching the effects of lead poisoning on Latinx youth, took to the streets of Santa Ana because she suspected the city was severely polluted with lead. Her findings were alarming. Nearly a quarter of the soil samples she collected showed unsafe levels of contamination — in some cases 20 or 30 times the safety standard set by the California Office of Environmental Health Hazard Assessment (OEHHA).
There was not a significant policy response from local and regional authorities at the time, but the community mobilized. Activists with Orange County Environmental Justice (OCEJ) began a campaign for the complete eradication of lead from Santa Ana. Their strategy was to leverage scientific data to organize the youth and push for equitable community-oriented policies. Their efforts were anchored in a community-science organizing model, which prioritized communal ownership of data with an aim to mobilize politically and enact change.
In practice, this OCEJ’s campaign required establishing strategic partnerships with scientists to design a data-collection plan to document the extent of urban contamination in Santa Ana. In 2018, OCEJ partnered with the University of California-Irvine (UCI) to conduct a thorough study of soil contamination in Santa Ana. Trained soil-sample collectors (mainly college students, OCEJ members, and local youth activists with Jovenes Cultivando Cambios) walked the streets of Santa Ana to sample soil in parks, residences, and streets. Scientists at UCI, then, analyzed the 1,500 samples collected and concluded that nearly half of these samples surpassed the OEHHA safety standard of 80 parts per million (ppm). In some cases, the measurements were as high as 2400 ppm. The areas that were the most polluted were also the poorest and with the highest proportion of Latinx residents.
I was in a meeting with OCEJ, sometime at the end of 2018, when I first heard about the lead crisis in Santa Ana. At that time, I was studying the history of smelters in Central Peru and the massive environmental degradation they had caused. And yet, I was struck by the pollution levels found by Yvette Cabrera. My first reaction was to ask whether there had been a refinery or any other metal industry in Santa Ana that could explain these soil-lead levels. “No that we know of,” said Enrique Valencia, OCEJ’s former director, “but residents would very much like to know what is going on.” After all, this was not like Flint, Michigan, where lead had reached water sources. In this case, lead was in the soil and the source of this pollution was unknown. “I think we need some historians to look into this,” I remember saying to Enrique.
That meeting with OCEJ was the beginning of a fascinating research journey for me. In 2020, by OCEJ’s initiative, I began leading an interdisciplinary research team of public health experts and historians to address a simple question: Where is all this lead coming from? The general strategy was to utilize archival documents (i.e., historical maps, industry directories, newspaper articles) to generate data that we can evaluate against the soil measurements collected by the OCEJ-UCI partnership.
Suspect #1: Lead Paint
First on our list of usual suspects for lead hazards was lead-paint. The lead industries introduced lead in paint in the early twentieth century to expand their market beyond toys, light bulbs, and other household products. Other countries, like Australia and several European countries, banned lead-paint due to safety concerns in the 1920s. Lead producers in the U.S., however, organized in large companies and trade groups (National Lead and later the Lead Industries Association), argued that lead was safe, and advertised its benefits aggressively. In the first half of twentieth century, this heavy metal made it in millions of homes in the U.S. Although the use of lead in paint peaked in the 1940s and was gradually phased out after that, lead-paint was not officially banned until 1978.
Could paint be the source of the large amounts of environmental lead found in Santa Ana? There is a lasting assumption that paint is the primary source of lead poisoning in the U.S. This is in part because house inspections, which are normally triggered after a child has shown high levels of lead in blood, usually find lead-paint in houses built before the 1960s and 1970s. And our study found geospatial evidence for that association. When we looked at the relationship between the age of buildings in Santa Ana and the levels of contamination in the city, we found a fairly strong correlation. The oldest part of town is also the most polluted. Does this mean, however, that the lead is coming from old buildings?
A few studies in the 1980s and 1990s cast serious doubts on this assumption. An important article by Howard Mielke, a prominent scientist of lead, argued that the association between paint and lead poisoning was at times spurious. A study of lead isotopes showed, in addition, that lead from paint chips could only explain part of the contamination in the immediate vicinity of old houses, but the lead in the soil found near roadways and parks had a different isotopic signature and, therefore, could not be attributed to paint at all. As we discovered, a different, more pervasive, source of contamination was affecting urban communities across the United States and the world.
Suspect #2: The Environmental Legacy of the Ethyl Corporation
In the 1980s, Howard Mielke testified at the U.S. Senate and advocated for a rapid phase out of leaded gasoline. At the time, combustion engines in the U.S. were emitting 34 thousand tons of lead into the atmosphere. By one estimate, about half of the lead produced in the world was being released as contamination, and leaded gasoline accounted for 90% of atmospheric emissions. Given these numbers, Mielke argued that a ban on leaded gasoline could wait no longer. Despite facing opposition from the gasoline industry and criticism from his own senator in the U.S. Congress, Mielke’s words were heard, and a phase-out of leaded gasoline was enacted in 1986.
The use of leaded gasoline in the twentieth century was an environmental justice issue. The lead emitted by cars was directly inhaled by urban dwellers and caused high levels of lead in their blood. These fine lead particles also deposited onto buildings and the soil around them, creating environmental hazards that do not decay or biodegrade. This reality was particularly acute among communities of color living in the heavily transited inner cities. During the height of leaded gasoline consumption, lead poisoning affected Black children at rates that were 6 or 7 times higher than white children. These high rates of lead in blood, as science keeps affirming, affects the development of children and their educational performance, even when they do not show physical symptoms of poisoning. Even today, lead poisoning continues to affect poor children and children of color disproportionately. The United Nations estimates that 1 in 3 children are currently poisoned with lead, primarily in developing nations.
The atrocious fact that lead was included in gasoline was not, however, an accident. The Ethyl Corporation (created by General Motors, Standard Oil, and DuPont) introduced leaded gasoline in 1923. Shortly after, when several workers became sick and died at one of their refineries, a series of public health investigations ensued. The Ethyl Corporation argued forcefully against public health experts who were raising the alarm about the hazardous nature of lead. Despite having important reservations, the use of leaded gasoline was nevertheless approved by U.S. Public Health Service. In the mid twentieth century, gasoline surpassed paint as the lead industry’s primary outlet for lead. The postwar boom meant more suburban development, more highways, and, naturally, more demand for gasoline-powered cars. In the 1960s, when psychiatrist Hebert Needleman (among others) showed that chronic exposure to lead affected the educational performance of children, scientists funded by the lead industry argued that lead was a natural occurrence in the body and, therefore, harmless. Despite the continuous objections of prominent public health experts, the use of lead as a gasoline additive continued to increase during the twentieth century, reaching its peak in the early 1970s.
Bringing History Back In
Given this history, could the past use of leaded gasoline better explain the soil-lead levels found in Santa Ana? Our interdisciplinary team addressed this question by investigating old roadway maps and generating a digital recreation of how roads were spatially distributed during different moments in history. We also used historical aerial images to estimate traffic flows in the past — mainly by counting the number of cars captured in each street at the moment the photograph was taken. These archival sources allowed us to correlate roadway networks and traffic flows in the past with current pollution levels. The results seemed to match earlier studies of leaded gasoline emissions. Traffic-related variables had a higher correlation with soil-lead than paint related variables. Although these two sources are difficult to isolate (mainly because older buildings in the downtown area happen to exist in the same areas that were exposed the most amount of traffic for the longest period of time), our mixture-analysis model estimated that gasoline was the most prominent and most likely contributor to soil-lead contamination in Santa Ana.
Figure 1: Historical Roadways and Contemporary Lead Pollution
The implications of this study extend beyond Santa Ana. There are many other communities that have a similar history of exposure to leaded gasoline. In southern California alone, the cities of La Habra, Fullerton, and parts of Los Angeles were likely exposed to heavy traffic during the twentieth century, particularly along the historical path of the 101 Highway. As a result, it is imperative that our systems for measuring the risk of lead exposure account for the historical legacy of leaded gasoline and provide the data needed for remediation policies at the community level. Meanwhile, in Santa Ana, the struggle continues.