Impact of Fuel Station Traffic Intensity on Heavy Metal, Polycyclic Aromatic Hydrocarbon, and BTEX Contamination of Soil and Road Dust: Distribution, Source Apportionment, Ecological Status, and Human Health Risk Assessment in Abuja Municipal Area Council, Nigeria

In the spaces between the pumps and the pavement of a busy city, a silent exchange is constantly taking place. Every time a vehicle stops to refuel, or drives past a station, it leaves behind a microscopic residue. This residue is a complex mixture of heavy metals, which are dense chemical elements that do not break down easily, and organic compounds like polycyclic aromatic hydrocarbons and BTEX. The latter are groups of chemicals found in gasoline and diesel that can evaporate into the air or settle onto the ground. Over time, these substances accumulate in the soil and in the fine layer of dust that coats our roads. While some of these chemicals are naturally present in the earth, human activity can concentrate them to levels that might affect the health of people living nearby, particularly children who play in the dirt and are more likely to ingest small amounts of it. Understanding exactly how much of these contaminants exists, where they come from, and what risks they pose is a critical task for environmental scientists working in rapidly growing cities.

A team of researchers recently turned their attention to the Abuja Municipal Area Council in Nigeria to investigate this exact problem. They focused on the area surrounding fuel stations, comparing sites with very heavy traffic to those with lighter traffic, and also checking areas far away from any fuel stations to establish a baseline. Their goal was to see if the intensity of vehicle movement around a gas station changed the amount of toxic substances found in the soil and the road dust. They collected samples from the top layer of the ground and from the dusty surfaces along the roads, then brought them to a laboratory to be analyzed for specific heavy metals like nickel, cadmium, vanadium, and lead, as well as the complex mix of hydrocarbons and volatile organic compounds mentioned earlier.

The results revealed a story that was more nuanced than a simple "more traffic equals more pollution" equation. When the researchers looked at the heavy metals, they found that the levels were surprisingly low across all locations, including the busiest fuel stations. The amounts of nickel, cadmium, vanadium, and lead found in the soil and dust were far below the safety limits set by Nigerian regulations for petroleum-impacted sites. In fact, the contamination levels were so low that the ecological risk to the environment was considered negligible. Even the most polluted samples contained only a tiny fraction of the metal concentrations that would trigger an intervention. This suggests that, at least regarding heavy metals, the fuel stations in this specific area are not acting as major sources of toxic accumulation in the ground.

However, the picture changed significantly when the researchers examined the organic compounds. While the heavy metals were low, the levels of polycyclic aromatic hydrocarbons and BTEX were much more notable, and their distribution was not what one might expect. The most striking finding was that the road dust collected from low-traffic fuel stations contained the highest concentrations of these harmful organic chemicals. In these specific dust samples, the researchers found a heavy buildup of high-molecular-weight compounds, which are the more complex and often more dangerous forms of these chemicals. One specific measurement, which estimates the cancer-causing potential of the mixture, reached a level in the low-traffic dust that was significantly higher than in the high-traffic areas or the control sites. This indicates that the nature of the contamination is not simply a result of how many cars pass by, but may be influenced by other factors such as how the fuel is handled, local wind patterns, or the specific way dust settles in quieter areas.

The health implications of these findings were assessed by calculating the potential risk to people who might accidentally eat or breathe in this dust. For the heavy metals, the risk to both adults and children was found to be very low, with no immediate threat of non-cancerous illness. But the organic chemicals told a different story. The researchers found that children face a higher risk than adults, primarily because they have a lower body weight and are more likely to put their hands in their mouths after playing in the dust. In the low-traffic fuel station dust, the estimated risk of developing cancer over a lifetime from ingesting this dust was higher than the standard safety benchmark used for screening. Similarly, the risk from ingesting dust containing BTEX chemicals was a concern for children, with the risk levels exceeding safety thresholds in several scenarios, driven mainly by total xylenes. While benzene posed a specific cancer risk, the non-cancer risks were dominated by xylenes. The study noted that inhalation and dermal contact pathways contributed negligibly to the overall risk compared to ingestion.

The study concludes that while the heavy metal contamination around these fuel stations is not a major concern, the organic pollutants require serious attention. The fact that the highest risks were found in the dust from low-traffic stations suggests that the problem is not just about the number of cars, but about how these chemicals settle and accumulate in the environment. The researchers emphasize that road dust acts as a reservoir for these pollutants, integrating them from vehicle exhaust, fuel spills, and evaporation. They recommend that future monitoring should focus more closely on these organic compounds, particularly in areas where dust can build up, and that better controls be put in place to manage fuel handling and prevent spills. The work highlights that in the complex environment of a city, the quiet corners can sometimes hold the most significant chemical burdens, and protecting public health requires looking beyond just the busiest roads.