Road dust is often described by environmental scientists as a chemical archive of urban life. Every time a vehicle brakes, a tire grinds against asphalt, or an engine burns fuel, trace amounts of metals are released into the environment, where they mix with soil particles and settle along roadsides. Industrial emissions, waste burning, mechanical workshops and even agricultural runoff add to this burden. Because these particles can be resuspended in the air by wind and traffic, or picked up on hands and food, they create multiple routes of human exposure: inhalation, ingestion and absorption through the skin. Prolonged exposure to heavy metals in roadside dust has been linked to respiratory and cardiovascular disease, cognitive impairment and a range of chronic conditions, making the humble dust particle a serious public health concern.

To quantify that concern, the team collected sixty dust samples from twenty sampling points spaced at least 300 meters apart along major roads in Ado-Ekiti, including high-traffic corridors such as Opopogboro, Adebayo, Okeyinmi and Igbaletere. At each location, ten-gram subsamples were combined into a composite sample to capture the local heterogeneity of surface dust. The samples were air-dried, sieved, ground into fine powder and digested using a mixture of sulfuric, hydrofluoric and perchloric acids before being analyzed with atomic absorption spectrometry at the Federal University, Oye-Ekiti. Strict quality control measures, including blank samples, instrument calibration and repeat analyses, were applied throughout, and all glassware was soaked in nitric acid for 24 hours to prevent contamination.

The results revealed a clear hierarchy of contamination. Zinc was the most abundant metal, at an average of 35.44 milligrams per kilogram of dust, followed by manganese at 32.36, copper at 21.26, lead at 12.66, cadmium at 2.70, chromium at 1.89, nickel at 0.73 and arsenic at 0.46. When these averages were compared with World Health Organization guideline values, most metals fell comfortably within safe limits. Cadmium, however, averaged 2.70 milligrams per kilogram against a WHO limit of 0.80, more than three times the threshold, and the study reports that lead concentrations also exceeded their guideline value. Individual sampling points told an even sharper story: site AD2 recorded the highest cadmium level at 10.26 milligrams per kilogram and the highest lead level at 26.20, while site AD10 consistently registered the lowest values, highlighting how sharply contamination can vary from one street corner to the next.

To understand where these metals come from, the researchers turned to geospatial analysis. Using QGIS and ArcGIS software with ordinary kriging interpolation on a 25-by-25-meter grid, they generated high-resolution maps of each metal’s distribution across the city. The patterns were strikingly non-random. Nickel and copper concentrations peaked in the northeastern and northwestern zones around Opopogboro and Better Life, areas dominated by heavy traffic, mechanical workshops and commercial activity. Zinc was elevated in the northern neighborhoods of Olorunsogo, Ifeoluwa and Palm Estate, consistent with tire wear, brake lining degradation and lubricating oils. Lead, by contrast, was highest in the southern districts of Igbaletere and Okeyinmi, a pattern the authors attribute to possible legacy residues from leaded petrol, waste incineration or informal battery recycling. Chromium hotspots in the northwest pointed toward construction activity and metal corrosion, while arsenic elevations in several quarters suggested combustion sources and waste burning.

Statistical tools added a second layer of source identification. The geoaccumulation index ranked cadmium as by far the most severely accumulated pollutant, with every other metal classified as unpolluted or only slightly contaminated. The contamination factor told the same story, placing cadmium first at 3.38, followed by arsenic at 1.53. Enrichment factors, which compare each metal’s abundance to natural background levels, revealed extreme anthropogenic enrichment for cadmium at 86.34 and lead at 51.11, meaning these metals overwhelmingly derive from human activity rather than the weathering of the local Proterozoic bedrock. Principal component analysis, which condensed the eight metals into two dominant factors explaining 80.28 percent of the total variance, separated a traffic-driven component containing nickel, lead, zinc, copper, arsenic and manganese from a second component loading on cadmium and chromium, hinting at distinct sources such as localized industrial discharges, fertilizer use or improper waste disposal.

The most consequential findings emerged from the human health risk assessment, which modeled daily intake doses for adults through ingestion, dermal contact and inhalation using standard exposure parameters, including a 60-kilogram body weight and a 20-year exposure duration. Zinc showed the highest average daily intake through ingestion at 4.23 times ten to the third milligrams per kilogram per day, with manganese and copper close behind, and it also led dermal absorption at 1.95 times ten to the third. But abundance is not the same as toxicity. When the calculated doses were weighted by each metal’s reference dose, the non-carcinogenic hazard indices for ingestion and dermal absorption exceeded safe limits for cadmium and lead, while inhalation risks remained comparatively low. In other words, the greatest danger comes not from breathing the dust but from accidentally swallowing it and from absorbing it through the skin, pathways that matter enormously in a setting where personal protective equipment is rarely used and hand-to-mouth contact is routine.

The carcinogenic risk calculations were equally sobering. The study identified cadmium and lead as the metals presenting the greatest lifetime cancer risk, with cadmium’s carcinogenic risk highest through ingestion and dermal exposure and lead following a similar pattern. Cadmium toxicity is associated with kidney damage, bone demineralization, increased fracture risk and cancers of the prostate, lung and kidney, while lead exposure is notorious for causing neurological impairment in children, anemia, nervous system dysfunction and elevated risks of hypertension and cardiovascular disease. Manganese, though within WHO limits on average, carries its own hazards of neurotoxicity and cognitive decline when concentrations climb. The authors note that the overall ecological risk indices for most metals remained low, suggesting that the immediate environmental threat to ecosystems is modest, but they caution that these general indices may not capture the vulnerabilities of specific urban receptors such as soil invertebrates, birds and small mammals that can bioaccumulate toxic metals.

The Ado-Ekiti findings echo a broader pattern documented across Nigeria and beyond. Similar studies in Lagos, Ibadan, Abeokuta and Osogbo have repeatedly found elevated concentrations of toxic metals in roadside dust, and comparable work in India and China links urban growth to traffic-driven metal pollution. This consistency suggests that roadside dust contamination is not a local anomaly but a systemic challenge facing fast-urbanizing cities, one that is likely to intensify as vehicle fleets expand and waste management lags behind population growth. The authors argue that Nigeria lacks localized environmental health guidelines adequate to the task, and they call for routine biomonitoring using sentinel species and bioavailability testing to capture real-world risks more accurately than generic indices allow.

The study closes with a practical agenda. Urban policymakers are urged to implement regular street cleaning, stricter vehicle emission controls, promotion of low-emission transport options and public education about the hazards of dust exposure, while health authorities should establish routine environmental monitoring and community-level interventions in the highest-risk neighborhoods. For the residents of Ado-Ekiti, the message embedded in the dust is clear: the metals shed by traffic, workshops and waste burning do not simply vanish, but accumulate in the fine particles that line the city’s streets, waiting to be inhaled, ingested or absorbed, and the time to intervene is before the next layer settles.

Subject of Research: Heavy metal contamination of roadside dust and associated human health risks in Ado-Ekiti, Nigeria

Article Title: Geochemical, geospatial, geoenvironmental and potential human health risk associated with dust particles in major roadsides in ado ekiti, Nigeria

Article References: Owolabi, J. T., Olusola, J. A., & Wole, A. (2025). Geochemical, geospatial, geoenvironmental and potential human health risk associated with dust particles in major roadsides in ado ekiti, Nigeria. Discover Toxicology, 2(1), Article 19. https://doi.org/10.1007/s44339-025-00037-7

Image Credits: AI Generated

DOI: 10.1007/s44339-025-00037-7

Keywords: road dust, heavy metals, cadmium, lead, Ado-Ekiti, Nigeria, health risk assessment, GIS mapping, urban pollution, atomic absorption spectrometry, carcinogenic risk, traffic emissions