Probabilistic Human Health Risk Assessment of Potentially Hazardous Elements in Urban Park Soils. Implications for Risk-Based Environmental Management: A Case Study in the Municipality of Caldas, Colombia
This study assesses probabilistic human health risks from potentially hazardous elements in urban park soils in Caldas, Colombia, identifying specific sites with elevated contamination levels and quantifying a significant probability of non-carcinogenic and carcinogenic risks for children to guide targeted environmental management.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The ground beneath our feet is rarely just dirt; it is a complex archive of human activity and natural processes. In cities, soil acts as a sponge, soaking up particles from car exhaust, industrial emissions, and the wear and tear of daily life. Over time, these particles can accumulate heavy metals and other potentially hazardous elements. While these substances occur naturally in the earth, their concentration in places where people play and relax raises a specific question: is the soil safe? Scientists approach this by measuring exactly how much of these elements are present and then modeling how people might interact with them. They consider two main ways people get exposed: accidentally swallowing tiny amounts of soil while playing, or having the soil touch their skin. By combining chemical measurements with these exposure scenarios, researchers can estimate the likelihood of health risks, distinguishing between a harmless patch of earth and one that requires attention.
In the municipality of Caldas, Colombia, a team of researchers set out to apply this kind of scrutiny to local urban parks. Caldas is a place where residential neighborhoods sit close to busy roads and industrial workshops, creating a setting where the soil could easily be contaminated. The team selected six locations for their study: five parks within the city and one site in a rural natural reserve, which they used as a baseline for comparison. At each location, they did not just take a single scoop of dirt. Instead, they collected thirty separate samples from different spots across the park, mixing them together to create a single, representative composite sample. This method ensured that their analysis reflected the overall condition of the park rather than just one lucky or unlucky spot. They focused on the finest particles of soil, those smaller than a grain of sand, because these are the ones most likely to stick to skin or be accidentally ingested by children.
Once the samples were prepared, the researchers used advanced laboratory equipment to measure the precise amounts of seven specific elements: arsenic, cadmium, nickel, lead, chromium, zinc, and copper. The results revealed a clear story of variation. Not every park was the same. One park, located near a ceramic tableware factory and a major road, showed the highest levels of arsenic, cadmium, and nickel. Another park, situated near metalworking shops and automotive repair facilities, contained the highest concentrations of lead, chromium, zinc, and copper. In fact, the lead levels in this second park were nearly five times higher than those found in the rural reference site, and the zinc levels were almost three times higher. The rural site, far from heavy traffic and industry, served as a quiet benchmark, showing what the soil looked like with minimal human influence.
To make sense of these differences, the researchers used statistical tools to see how the elements moved together. They found that the parks near the ceramic factory and the metal shops had distinct chemical "fingerprints" that set them apart from the others. While the study could not pinpoint the exact source of every particle, the proximity of these parks to specific industries and heavy traffic suggested that human activity was the primary driver of the elevated levels. The researchers then compared the urban parks to the rural site using several standard calculation methods. These comparisons consistently highlighted the same two parks as having the most significant contrasts with the cleaner rural soil, flagging them as the areas that needed the most attention.
The final step was to ask what these numbers meant for the people using the parks. The researchers built a computer simulation to model the health risks for both children and adults over a lifetime of recreational use. They ran the simulation ten thousand times, varying factors like how often a person visits the park, how much soil they might accidentally swallow, and their body weight, to create a realistic picture of risk. The results showed that for adults, the risk remained very low across all locations. For children, however, the picture was different. In the park near the ceramic factory, the simulation suggested that there was a roughly one-in-four chance that the combined exposure to these elements could exceed a safety threshold for non-cancer health effects. This does not mean that children are currently getting sick, but rather that the potential for harm is high enough to warrant further investigation.
The study also looked at the risk of cancer, specifically from arsenic. Because the researchers had to make assumptions about the chemical form of the arsenic and how easily it is absorbed by the body, they treated this as a screening estimate rather than a definitive diagnosis. Even with these conservative assumptions, the simulation indicated that in the park near the factory, the estimated cancer risk for children fell into a range that experts consider significant enough to manage. In contrast, the other parks showed much lower risks. The researchers concluded that while the data does not prove that the soil is dangerous, it strongly suggests that the two parks with the highest concentrations should be the priority for follow-up testing. They recommend gathering more detailed information, such as local attendance patterns and specific chemical forms of the metals, to refine the assessment. Until then, the study serves as a clear signal that in the complex landscape of urban Caldas, not all parks are created equal, and some deserve a closer look to ensure they remain safe havens for the community.
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