A biologist at the University of Miami College of Arts and Sciences advises consumers to think twice when deciding which chocolate bar they want to eat. That's because a heavy metal often found in chocolate might not just affect their health, but also the health of their future children.
"You're getting a little bit more than a kiss in your Hershey's," said Delia Shelton, referring to a Consumer Reports investigation that found concerning levels of the heavy metals cadmium and lead in many brands of chocolate. Shelton, an assistant professor in the Department of Biology, studies cadmium toxicity in zebrafish—a species that is 74 percent genetically similar to humans.
Cadmium, a toxic heavy metal, is found in many foods that humans consume, including rice, tortillas, and shellfish. Excessive levels of cadmium intake can lead to adverse effects on the heart and other serious health problems. Cadmium also has a half-life of 10 to 30 years, meaning that it takes decades for the body to entirely expel the toxin once consumed. Based on this fact, Shelton hypothesized that the effects of cadmium exposure could be passed from one generation of zebrafish to their offspring and grandoffspring.
To test this hypothesis, Shelton collaborated with Amanda Oehlert, an assistant professor in the Rosenstiel School of Marine, Atmospheric, and Earth Science's Department of Marine Geosciences. Using equipment from the Oehlert Biogeochemistry Lab and from Shelton's lab, the Environmental Psychology Innovation Center, Shelton studied how zebrafish react to cadmium.
Her hypothesis proved correct for zebrafish, which indicates that the same could be true in humans. "What we see is that cadmium does have these multi-generational effects," she explained.
This finding has important implications for understanding the environmental determinants influencing human health. That includes the health of people in Miami-Dade County affected by the "Old Smokey" Trash Incinerator, which spewed high levels of cadmium into West Coconut Grove for 45 years. The Environmental Justice Clinic at the School of Law is involved in seeking medical monitoring for residents exposed to the incinerator's toxic ash and pollution, and Shelton's findings about the multi-generational impacts of cadmium exposure in zebra fish could have implications for this effort.
The National Institute of Environmental Health Sciences has awarded Shelton more than $1.1 million since 2020 to support her cadmium research, including new research testing therapeutic treatments for cadmium-induced heart disease.
Students working in Shelton's lab have been recognized for their role in the lab's findings. Olaedo Umeh and Gabriella Guevara, two undergraduate research assistants, placed third at the 2025 Miller School of Medicine Eastern-Atlantic Student Research Forum. Additionally, Ph.D. student Jessica Okutsu was designated as a Frost Institute for Data Science & Computing fellow and received a National Science Foundation Graduate Research Fellowship Honorable Mention.
"The students working in my lab are superstars, and my research accomplishments would not be possible without them," Shelton said.
