Two UCI-led studies point to gasoline emissions as the likely source of soil lead contamination in Santa Ana

Two recent studies conducted by researchers at the University of California, Irvine have shown a strong correlation between lead concentrations in the soil and historical vehicle emissions, specifically in urban, disadvantaged neighborhoods across Santa Ana, Calif. The researchers used a community-based approach to investigate environmental injustices that exist in the predominantly-Hispanic community.

Lead (or Pb), which is considered an environmental toxicant, has been associated with a wide range of adverse health conditions and, as a result, disadvantaged communities in the city of Santa Ana have been disproportionately affected by this environmental burden.

Both studies were based on a community-based approach, which coalesced environmental activists, a youth collective, and UCI researchers from various disciplines. The research coalition came together in 2018 as part of the Lead-Free Santa Ana campaign (or PloNo!) spearheaded by Jovenes Cultivando Cambios and Orange County Environmental Justice.

Since a central concern among residents of Santa Ana was to learn where the lead was coming from, Orange County Environmental Justice gathered an interdisciplinary research team of public health experts and historians to investigate the sources of soil contamination in the city.

The first study, led by Juan Manuel Rubio, PhD, a historian and UCI Mellon Humanities Faculty Fellow and Shahir Masri, ScD, assistant specialist of environmental and occupational health at the UCI Program in Public Health, sought to utilize archival documents (i.e. historical maps, industry directories, newspaper articles) to generate data that could be evaluated against the soil measurements collected by the community-academic partnership.

The team collected and analyzed soil samples taken from locations throughout Santa Ana and produced detailed measurements of soil lead based on those samples. The results helped to extract two potential sources of lead contamination from the past – lead-paint and leaded gasoline. The researchers concluded that while contemporary traffic volumes do not correlate with soil-lead concentrations, historical traffic patterns have an important predictive value in mapping high concentrations of current lead levels in the environment.

Findings were published in the journal Environmental Research.

“The current approach used by public health agencies to prevent lead poisoning, which is primarily focused on lead-paint and consumer products, is overlooking leaded gasoline as a major source of environmental lead,” Rubio said. “Our results also indicate that legacy soil-lead may be present in many other urban environments that received similar flows of traffic to Santa Ana during the twentieth century.”

These results were consistent with the historical record of the lead industry, which showed that leaded gasoline represented the largest source of lead emissions into the environment in the twentieth century. Historical research allowed these scholars to understand how the city grew over the twentieth century and how traffic flowed, thereby providing crucial information for understanding the location of contemporary lead hazards.

“We used what is known as a ‘mixed-model’ approach by combining statistical and historical methods, and it’s really what made our work here unique,” said senior author of the study, Jun Wu, PhD, a professor of environmental and occupational health at the UCI Program in Public Health. “This mixed-model showed that, although we cannot rule out leaded paint as a source, leaded gasoline was the most likely and most prominent contributor to the soil lead crisis in Santa Ana. Our study demonstrates the value of applying historical research for preventing lead poisoning and addressing environmental injustices.”

To further determine whether the lead contamination could be traced to specific sources, especially historical gasoline emissions, a second team of researchers conducted a separate quantitative source-related analysis that examined lead isotopes in nearly 130 soil samples at different depths. This analysis revealed a strong correlation with lead concentrations and vehicle emissions proxies (e.g., distance to roads) – reinforcing the likelihood of the elevated levels being due to human activity as the likely source.

Findings were published in the journal Toxics.

Isotypes are members of a family of a chemical element that all have the same number of protons but different numbers of neutrons. Studying isotopic signatures can provide valuable information regarding the source of soil contamination. Different lead products contain different radiogenic Pb isotope to stable Pb ratios, depending on the geographical origin of the lead used in manufacturing. As with the first study, understanding the history of lead mining and the lead industry is crucial to interpreting the variation in isotopic signatures.

“Our studies underscore the need for public health officials and city managers to respond to community concerns about environmental justice issues,” said corresponding author Shahir Masri, ScD. “It also demonstrated how working directly with communities on public health interventions can be a powerful and effective way to bring about positive change.”

Additional co-authors of the Environmental Research publication include Alana M.W. LeBrón, PhD, assistant professor of health, society and behavior who has a dual appointment in the Department of Chicano/Latino Studies at the UCI School of Social Sciences, Michael Logue, PhD, an assistant project scientist; Keila Villegas and Patricia Flores, both with the Orange County Environmental Justice; Abigail Reyes with the UCI Office of Sustainability’s Community Resilience Projects; and PhD students Ivy Torres and Yi Sun with the UCI Program in Public Health.

Additional co-authors of the Toxics publication include Jun Wu, PhD; Alana M.W. LeBrón, PhD; Juan Manuel Rubio, PhD; Michael Logue, PhD; Patricia Flores; Abel Ruiz with Jóvenes Cultivando Cambios; and Abigail Reyes.


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