Urban soils in Africa are increasingly contaminated by toxic heavy metals due to rapid urban expansion, industrialisation, traffic emissions, and inadequate waste management. Toxic heavy metals such as lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), and nickel (Ni) are of major concern because of their persistence, bioaccumulation potential, and ecological risks for the environment and humans. This systematic review synthesises evidence from 38 peer-reviewed studies published between 2010 and 2024 on the concentrations and sources of toxic heavy metals in urban soils of Africa. The results demonstrated an uneven research distribution on toxic heavy metals across different countries of Africa, with Nigeria and Ghana most represented, while large regions, including countries such as Egypt and Ethiopia, remain poorly studied. Industrial activities (27%) and traffic emissions (26%) accounted for more than 50% of the reported contamination sources, followed by domestic waste disposal (18%) and agricultural inputs (10%). Weighted mean concentrations of Pb, Cd, and Cr in many countries exceeded FAO permissible limits, indicating a significant threat to humans and the environment. Microwave digestion was the most commonly used extraction method, while X-ray fluorescence has gained increasing application. The findings demonstrate widespread contamination from rapid urbanisation and industrialisation but highlight limited research done on toxic heavy metals in urban areas of most African countries. Future research should focus on quantifying the metal concentration in African countries, where limited work has been done; the bioavailable fractions of toxic heavy metals and possible remediation strategies to improve soil quality in urban areas. ( 2020 ) Domestic and industrial wastes; Municipal and industrial drainage; sewage sludge and irrigation with wastewater X-Ray Fluorescence Spectrometer R 3.3.3 Cr = 58.1; Ni = 30.6 n = 15 Monitoring trace elements in urban farming soils is crucial to prevent contamination and ensure ecosystem health, as these elements can enter the human food chain through plants Kenya East Africa Benhaddya et al., 2016 Traffic Emissions and Industrial Activities Microwave digester/Atomic absorption spectrometer SPSS 16.0 Ni = 38.5; Pb = 180. Legislation and enforcement in the informal industrial sector are needed to safeguard health and environmental quality Zimbabwe Southern Africa Iwegbue and Martincigh ( 2018 ) Industrial n = 82 The study highlights the need for urban planning and management to incorporate health risk assessments to ensure a sustainable environment Nigeria West Africa Boudia et al., 2019 Industrial Activities; Traffic: Vehicular emissions Microwave digester/ICP-AES SPSS 24.0.0 As = 10.9; Cr = 55.0; Ni = 27.5; Pb = 52.2. n = 64 The findings highlight the need for monitoring and managing soil contamination in urban areas to mitigate ecological and health risks Nigeria West Africa Bellarbi et al., 2015 Urban activities; Traffic emissions; Industrial Sources; Agricultural Sources; The use of wastewater for irrigation Microwave digester/ICP-AES/ICP-MS - Cr = 75; Ni = 41.3; Pb = 64.8. n = 3 The findings highlight the need for better pollution control and wastewater management in Fez to prevent environmental risks and ensure safe agricultural practices Morocco North Africa Adedeji et al., 2019 Anthropogenic sources; including emissions from artisan workshops, road traffic, and incineration at dumpsites. n = 30 The findings highlight the need for monitoring and managing urban soil contamination to mitigate public health risks associated with arsenic exposure Tanzania East Africa Beroigui et al., 2020 Airborne Deposits; Industrial activities. This includes emissions from road traffic Microwave digester/ICP-OES SPSS 10 As = 6.39; Cr = 19.0; Ni = 15.6; Pb = 56.4; Cd = 0.52. n = 18 The findings highlight the need for monitoring and managing soil quality in urban areas to protect public health, especially for vulnerable populations like children Morocco West Africa Maas et al., 2010 Industrial emissions; Traffic; Agricultural activities Microwave digester/Atomic absorption spectrometer R 2.5.1, gstat 09.−39 and pgirness 1.3.3 Cd = 0.44; Cr = 30.9; Pb = 53.1. n = 9 The contamination levels indicate a substantial risk of ecological harm and possible human exposure, particularly if these soils are used for agricultural activities. The authors stress that the elevated levels of these metals, especially in combination with the acidic soil pH which enhances metal mobility and uptake by plants, render these soils unsuitable for food production. n = 25 The study highlighted the potential contamination of ground water through leaching of the trace elements especially in soils which are highly permeable, threatening drinking water quality Nigeria West Africa Githaiga et al., 2021 Intensive traffic; Industrialisation; Urbanisation; Solid waste Microwave digester/X-ray fluorescence spectrometer and ICP-MS - Pb = 10.8; Cd = 0.67; Cr = 27; As = 26; Ni = 16.3. n = 7 (urban lands only) The study highlights the need for integrated managed of agriculture and industrial waste production to mitigate pollution Kenya East Africa Konadu et al., 2023 Automotive activities; anthropogenic inputs; Industrial and traffic emissions XRF Fluorescence R tool 4.2.2 As = 54.3; Cd = 54.6; Cr 65.7; Ni 564. Despite these limitations, clear patterns emerge regarding localised hotspots, dominant contamination sources, and the metals of highest concern. Lead (Pb), Cr, Ni, and Cd consistently appear as major contaminants, often exceedingly internationally recognised permissible thresholds, which suggests widespread environmental and human health risks. Industrial activities and traffic emissions accounted for more than half of the identified contamination sources, while domestic waste disposal, e-waste recycling, and agricultural inputs also contributed substantially.

year, equating to 8–10% of total global emissions. Carbon dioxide is a greenhouse gas, meaning it causes heat to get trapped in the atmosphere, rather than Human impact on the environment (or anthropogenic environmental impact) refers to changes to biophysical environments and to ecosystems, biodiversity, and natural resources caused directly or indirectly by humans. Modifying the environment to fit the needs of society (as in the built environment) is causing severe effects including global warming, environmental degradation (such as ocean acidifica The air pollutants released from the burning of fossil fuels usually comes back to earth in the form of acid rain. Acid rain is a form of precipitation which has high sulfuric and nitric acids, which can also occur in the form of a fog or snow. Acid rain has numerous ecological impacts on streams, lakes, wetlands and other aquatic environments. It damages forests, robs the soil of its essential nutrients, and releases aluminium in the soil, which creates difficulties in the absorption of water for local plant life. Researchers have discovered that kelp, eelgrass and other aquatic vegetation absorbs carbon dioxide and hence reduces ocean acidity. Scientists, therefore, say that growing these plants could help in mitigating the damaging effects of acidification on marine life. T… Their lifestyle (including overall affluence and resource use) and the pollution they generate (including carbon footprint) are equally important. In 2008, The New York Times stated that the inhabitants of the developed nations of the world consume of the FAO estimated that 18% of global anthropogenic GHG (greenhouse gas) emissions (estimated as 100-year carbon dioxide equivalents) are associated in some way with livestock production. FAO data indicate that meat accounted for 26% of global livestock product tonnage in 2011. Globally, enteric fermentation (mostly in ruminant livestock) accounts for about 27% of anthropogenic methane emissions, Despite methane's 100-year global warming potential, recently estimated at 28 without and 34 with climate-carbon feedbacks, methane emission is currently contributing relatively little to global warming. In the US beef production system, practices prevailing in 2007 are estimated to have involved 8.6% less fossil fuel use, 16% less greenhouse gas emissions (estimated as 100-year carbon dioxide equivalents), 12% less withdrawn water use and 33% less land use, per unit mass of beef produced, than in 1977. From 1980 to 2012 in the US, while population increased by 38%, the small ruminant inventory decreased by 42%, the cattle-and-calves inventory decreased by 17%, and methane emissions from livestock decreased by 18%; yet despite the reduction in cattle numbers, US beef production increased over that period. Some impacts of meat-producing livestock may be considered environmentally beneficial. The failure of noticing and appreciating plants is regarded as "plant blindness", and this is a worrying trend as it puts more plants at the threat of extinction than animals. Our increased farming has come at a higher cost to plant biodiversity as half of the habitable land on Earth is used for agriculture, and this is one of the major reasons behind the plant extinction crisis. Defaunation is the loss of animals from ecological communities. === Invasive species === Invasive species are defined by the U.S. Department of Agriculture as non-native to the specific ecosystem, and whose presence is likely to harm the health of humans or the animals in said system. Such massive alteration of the global carbon cycle has only been possible because of the availability and deployment of advanced technologies, ranging in application from fossil fuel exploration, extraction, distribution, refining, and combustion in power plants and automobile engines and advanced farming practices. Livestock contributes to climate change both through the production of greenhouse gases and through destruction of carbon sinks such as rain-forests. According to the 2006 United Nations/FAO report, 18% of all greenhouse gas emissions found in the atmosphere are due to livestock. It damages forests, robs the soil of its essential nutrients, and releases aluminium in the soil, which creates difficulties in the absorption of water for local plant life. Researchers have discovered that kelp, eelgrass and other aquatic vegetation absorbs carbon dioxide and hence reduces ocean acidity. Scientists, therefore, say that growing these plants could help in mitigating the damaging effects of acidification on marine life. === Ozone depletion === === Disruption of the nitrogen cycle === Of particular concern is N2O, which has an average atmospheric lifetime of 114–120 years, and is 300 times more effective than CO2 as a greenhouse gas. Surface mining of oil shale deposits causes the usual environmental impacts of open-pit mining. In addition, the combustion and thermal processing generate waste material, which must be disposed of, and harmful atmospheric emissions, including carbon dioxide, a major greenhouse gas. Experimental in-situ conversion processes and carbon capture and storage technologies may reduce some of these concerns in future, but may raise others, such as the pollution of groundwater. === Petroleum === The environmental impact of petroleum is often negative because it is toxic to almost all forms of life. Some pesticides contribute to global warming and the depletion of the ozone layer. === Pharmaceuticals and personal care === == Transport == The environmental impact of transport is significant because it is a major user of energy, and burns most of the world's petroleum. This creates air pollution, including nitrous oxides and particulates, and is a significant contributor to global warming through emission of carbon dioxide, for which transport is the fastest-growing emission sector. By subsector, road transport is the largest contributor to global warming.

Urban air pollution, specifically Nitrogen Dioxide (NO2), presents a multifaceted challenge that is intricately coupled with the stochastic, multi-modal, and non-linear dynamics of mega-city traffic systems. This study systematically investigates the non-linear impacts of mixed traffic flow-comprising motorcycles (MC), private cars (PC), and heavy vehicles (BT)-on local air quality at the iconic Bundaran HI intersection in Jakarta, Indonesia. Leveraging a high-resolution, year-long longitudinal dataset, we developed a robust Random Forest (RF) modeling framework integrated with Permutation Importance and Partial Dependence Analysis (PDP) to decipher the environmental footprint of urban transport under tropical conditions. Our results reveal that private car volume and the Volume-to-Capacity (V/C) ratio act as the primary catalysts for NO2 spikes, significantly outweighing the contribution of heavy vehicles in this specific urban corridor. Crucially, a distinct non-linear threshold effect was identified: NO2 concentrations undergo a regime shift, rising exponentially once the V/C ratio exceeds a critical "elbow" of 0.65. This non-linearity indicates that traditional linear mitigation strategies and average-speed-based emission models significantly underestimate pollution risks during saturated traffic states. Policy scenario simulations demonstrate that a 30% reduction in private vehicle volume yields a 5.8% reduction in mean NO2, offering nearly six times the environmental utility of heavy vehicle restrictions. Furthermore, the study explores the role of road surface materials-specifically Stone Mastic Asphalt (SMA)-and meteorological interactions in exacerbating localized pollution. This research provides a data-driven, interpretable framework for urban planners to transition from generic traffic bans toward precision-based, sustainable management strategies that align with the core principles of cleaner production, urban resilience, and UN Sustainable Development * E-mail: xgguo@psu.edu 22 6 2026 2026 21 6 514669 e0350301 9 2 2026 12 5 2026 22 06 2026 23 06 2026 23 06 2026 © 2026 Hou et al 2026 Hou et al https://creativecommons.org/licenses/by/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Urban air pollution, specifically Nitrogen Dioxide (NO 2 ), presents a multifaceted challenge that is intricately coupled with the stochastic, multi-modal, and non-linear dynamics of mega-city traffic systems. Our results reveal that private car volume and the Volume-to-Capacity (V/C) ratio act as the primary catalysts for NO 2 spikes, significantly outweighing the contribution of heavy vehicles in this specific urban corridor. Crucially, a distinct non-linear threshold effect was identified: NO 2 concentrations undergo a regime shift, rising exponentially once the V/C ratio exceeds a critical “elbow” of 0.65. This non-linearity indicates that traditional linear mitigation strategies and average-speed-based emission models significantly underestimate pollution risks during saturated traffic states. Derived metrics included the Volume-to-Capacity (V/C) ratio, average Velocity (V), and Passenger Car Equivalent (PCE) values adjusted for Indonesian traffic characteristics (where MCs have a PCE of 0.25 and BTs range from 1.3 to 2.5). Air Quality Monitoring: Data for NO 2 , PM10, PM2.5, SO 2 , CO, and O 3 were extracted from a government-operated monitoring station located within the Bundaran HI precinct (approx. 50m from the traffic flow). Meteorological Data: To account for atmospheric dispersion, we integrated hourly parameters for Temperature (T), Relative Humidity (RH), Wind Speed (WS), and Rainfall. Interestingly, as shown in Fig 1 , NO 2 fluctuations track the trajectory of PC more closely than MC, despite the numerical dominance of the latter. This decoupling indicates that the higher-temperature combustion processes in larger car engines potentially possess a higher NO 2 emission intensity per unit compared to the smaller engines of motorcycles. This suggests that car-pooling or car-reduction policies might yield more significant air quality benefits than focusing solely on motorcycle regulation. 3.2. Correlation and Inter-pollutant Synergy Fig 2 provides a quantitative overview of the linear relationships between NO 2 concentrations, traffic dynamics, and meteorological variables. The “State of Traffic” vs. Volume: Among traffic-related variables, Total_BusTruck and IsWeekend exhibit higher sensitivity than individual vehicle counts. Interestingly, the model identifies Total_VCRatio and Total_Car as critical, but secondary to meteorological dissipation factors. This suggests that while traffic provides the “source term,” the atmospheric “capacity” to disperse these emissions (governed by wind and temperature) is the primary determinant of observed concentration levels at the Bundaran HI station. Heavy Vehicle Restriction (Scenario 2): This intervention yielded the most significant environmental benefit, achieving a 6.9% reduction in mean NO 2 concentrations. This aligns with the “high-leverage” impact of heavy-duty vehicles (HDVs) observed in urban emission inventories [ 31 ]. This confirms that HDVs are the highest-leverage points for intervention, as their massive engine displacement In reality, a significant reduction in car volume might trigger an increase in average speed (a rebound effect), potentially altering the emission profile in a complex manner. Transitioning to Threshold-Based Management: Collectively, the results from Figs 5 and 6 suggest that “blanket bans” on specific vehicle classes can be environmentally ineffective if they do not address the underlying “state” of the traffic. Precision management should instead focus on maintaining the V/C ratio below the 0.65 threshold.

Traffic is a major source of green house gases. The transport field stands for 32 % of the energy consumption and 28 % of the total CO2 emissions, where road transports alone causes 84 % of these figures. The energy consumed by a car traveling at constant speed, is due to engine ineffiency, internal friction, and the energy needed to overcome resisting forces such as aerodynamic drag and rolling resistance.Rolling resistance plays a rather large role when it comes to fuel economy. An improvement in rolling resistance of 10 % can yield fuel consumption improvements ranging from 0.5 to 1.5 % for

Heavy metals in street dust are one of the most important sources of pollutants in urban areas. This urban dust can be caused by industrial activities, traffic, erosion of buildings, and fossil fuels. The aim of this systematic review is to evaluate the ecological risk of heavy metals in the dust of Iran's provinces. This study was conducted in February 2023 in order to investigate the environmental risks associated with heavy metals associated with dust particles in Iran. The present study was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Finally, 9 studies were extracted from the search databases. The ecological risk of heavy metals in the present study was as follows: Cd (258.26؛ CI: 83.53, 433) >Pb (52.58؛ CI: 37.15, 68.02) >Cu (24.44؛ CI: 16.74, 32.14)>Ni (14.75؛ CI: 12.68, 16.82)>As (13.53؛ CI: 10.20, 16.85)>Zn (6.32؛ CI: 3.76, 8.87)>V (3.18؛ CI: 2.65, 3.72)>Cr (2.73؛ CI: 2.19, 3.27)>Co (1.94؛ CI: 1.13, 2.74). The mean ranking of the studied Pb ecological risk is as follows: Shiraz.> Tehran > Ahvaz > Ilam > Abadan > Dezful. The ecological risk potential of Cd in Tehran was also much higher than the standard. Therefore, Tehran was the most polluted city studied in terms of the ecological risk potential of Cd (1611.41؛ CI: 1605.98, 1616.84) and Pb (86.54؛ CI: 71.46, 101.62). The average concentration as well as the ecological risk of Cr, Co, and V metals were lower than the standard. Therefore, controlling the sources of heavy metal emissions (especially lead and cadmium) is highly recommended.

Objective: Dessie is the trade center for northeast Ethiopia. High traffic flow plus overacting of promotion made the city noisy. There is a shortage of relevant evidence that enforces policy makers to design intervention plans. Therefore, this study aimed to explore the health-risky road traffic noise pollution in Dessie City, Ethiopia. Methods: The study was conducted by purposive selection of the study area and sampling sites of the city from May 31, 2021 –June 6, 2021. Noise level recordings were taken by a digital Sound Meter and location data was collected by Global Positioning System. R