According to the study, published in the current issue of Soil and Sediment Contamination, the concentration of these pollutants is higher than that found in other large cities, including Chicago, London and Helsinki. However, they are lower than in New Orleans and Detroit.
The studied spanned just over 55 square miles of the Miami area with more than 85 percent of the surface covered by parking lots, streets, large buildings, shopping centers, houses and other impervious structures.
“We expected to find these high amounts,” said Gurpal Toor, a researcher with UF’s Institute of Food and Agricultural Sciences. “This is the first preliminary study of these chemical levels in this area, and it confirms what everyone suspected.”
The pollutants, 16 types of chemicals known as polycyclic aromatic hydrocarbons or PAHs, have been identified by the U.S. Environmental Protection Agency as “priority pollutants” — those that are both common and toxic.
PAHs largely come from man-made activities, primarily the burning of fossil fuels — although one of the most common PAHs found in the Miami soil, Benzo(a)anthracene, is also one of the most prominent carcinogens in cigarette smoke.
Early reports of human exposure to PAHs were noted in 1775 by British surgeon Percival Pott, who observed that chimney sweeps in London had a higher incidence of scrotal cancer.
In 1875, other researchers noted elevated skin cancers in workers in the coal tar industry; coal tar is rich in PAHs.
“These chemicals are virtually everywhere — especially in urban areas,” said Toor, an assistant professor of soil and water science at IFAS’ Gulf Coast Research and Education Center. “We live with them every day, and have for a long time.”
The PAHs can be absorbed by the human body through ingestion, inhalation and even through the skin, although it’s not well known how much of the pollutants might be transmitted to people from soil.
However, elevated amounts of these chemicals can be harmful to soil microorganisms and may accumulate in the food chain.
The researchers collected samples at depths of approximately 15, 30 and 45 centimeters from 21 residential areas, nine public parks, nine public buildings and six commercial areas in Miami.
All samples collected near the top of the soil contained more than 1,000 micrograms of PAHs per kilogram of soil — the definition of heavy contamination according to an internationally used scale. Analysis of the PAHs revealed that the vast majority were most likely from vehicle exhaust.
Simply put, the Miami soil may have such high contamination because there are so many cars in the area.
“You would expect to find high levels in these sorts of areas that very close to sources of the pollution,” said Stephen Roberts, director of the UF Center for Environmental and Human Toxicology. “From the perspective of the [Environmental Protection Agency] I think these levels wouldn’t be seen as unusual.”
The importance of the study, Toor said, was that it created a baseline against which future measurements can be evaluated, to tell if attempts to limit pollution are working.