Roadside soil samples were collected from four sites (heavy traffic area (Wurukum); industrial site (Gboko road); residential area (Federal Lowcost) and FederalMedicalCenter(Wadata) representing different activities across the Benue Metropolis. At each of the sample site, roadside soils were collected at different distance from the edge of the main road (2, 10, 30, 40 and 60 meters). In each of the distance, roadside soil were collected at three depth of 0 -1 cm, 2 -4 cmand 4 - 6 cm for the determination of pH, organic matter, organic carbon, Cu, Cd, Fe, Pb, As, Mn, Zn, Cd and Ni. pH, electrical conductivity (EC), organic matter and organic carbon were determined using standard procedures, while heavy metals were determined using Perkin-Elmer Analyst 300 Atomic Absorption spectroscopy (AAS). Zinc was observed to show the higher levels in all the sampling sites, such higher level can be related back to the wear-and-tear of vehicle components as a result of the stop-start traffic patterns and brake pads. The concentrations of all the metals in the four sampling sites decreased exponentially with distance from the edge of the road and dropped to the minimum levels at about 60 meters. Similarly, mean concentrations of Cu, Fe, Pb, As, Mn, Zn, Cd and Ni were significantly higher around the industrial area (Gboko road) and heavy traffic (Wurunkum) areas than other sampling areas followed an increasing trend with the increase in depth. The vertical movement of all the metals, exhibited predominant association with soil pH and organic carbon. From the results of this study, the pH of the roadside soils from all the sampling points ranged from 4.56 to 7.71, which enhances increased of heavy metals down the soil profiles. Organic carbon content ranged of 0.27% to 5.44% across all the sampling points appears to increase the mobility of all the metals to a depth6 cm. The values of the heavy metals suggest that automobiles and traffic activities are a major source of these metals in the roadside soil within the study area. Also, with the exception of Pb, Fe and Cd, the levels of Cu, As, Mn, Zn and Ni in the present study were lower as compared with results found by other researcher in various countries worldwide.
Urban soils act as a sink for heavy metals and other pollutants, possible sources of which are mainly from anthropogenic activities such as vehicular emissions [
The Soil forms chief component of an ecosystem and is the most endangered due to influence of various human activities related to Industrial, Agricultural, and Urban development [
Air pollution can cause health problem, it can also damage the environment and property. It causes the thinning of the protective ozone layer of the atmosphere thus leading to climate changes. Air pollution results from a variety of causes not all of which are within human control. Probably the most important natural sources of air pollution are dust storms for desert areas and volcanic activity which sometimes pour large amount of ash and toxic chemical and particulates into the atmosphere. Globalization and civilization have led to air getting more and more polluted over the years. Air pollution is caused by both natural and man made sources. Major man made sources of ambient air pollution include industries, automobiles and power generation in indoor environment, tobacco smoke and combustion of solid fuel for cooking and heating are the most significant sources. Fuel combustion is the primary source of a large number of health damaging air pollutants including fine and respirable particulates matter, carbon monoxide (CO), Suphur dioxide (SO2), nitorgen oxides (NOx), volatile organic compounds (VOCs), Ozone (O3) and atmosphere lead. Some of these pollutants are directly by products of fuel combustion, but others such as ozone are formed in the air through chemical reaction with other agent in the atmosphere.
Heavy metals are natural component of the earth crust unlike organic pollutants, which are broken down to greater or lesser extent depending on their activity, metals degraded and will remain in the soil permanently unless they are re-suspended and relocated by wind or leached out.
Soil pH is an indication of the acidity or alkalinity of the soil and is measured in pH units. Soil pH is defined as the negative logarithm of the hydrogen concentration. The pH scale goes from 0 to 14 with pH 7 as the neutral point. As the amount of hydrogen ions in the soil increase the soil pH decreases thus becoming acidic. From pH 7 to 0 the soil is increasingly more acidic and from PH 7 to 14 the soil is increasingly more alkaline or basic. One of the most important Pb sources in an urban environment is vehicle emission. In recent years, numerous studies have assessed the influence of traffic emissions on the levels of Pb. [14-16] shows that the combustion of leaded gasoline was the primary source of Pb, in addition some workers have reported a positive correlation between Cu, Zn and Pb and have interpreted it as derivation of the same source of contaminants [17,18]. Similarly, the environmental chemistry of chromium has been widely studied [
Makurdi, capital of Benue state located between latitude 7˚44'0"N and longitude 8˚32'0"E it occupies a land area of about 34,059 square km with an estimated population of about 5,181,642. Makurdi has a distinct season. The rainy season which runs from the month of April to October and dry season from the month of November through the end of April. The temperature ranges from 43˚C to 24˚C during the dry season and in the rainy season temperature ranges from 28˚C to 32˚C. There are some industries that greatly pollute the environment through gaseous emission. Markurdi Metropolis is polluted by both vehicular and industrial activities which might contain heavy metals that can affect humans upon inhalation. Hence, the need for this study.
Samples were collected in Makurdi located in Benue State, Nigeria. Samples were collected from heavy traffic area (Wurukum); industrial site (Gboko Road); residential area (Federal Lowcost) and Federal Medical Center (Wadata) in Makurdi, Benue State, Nigeria. At each of the sampling site, samples were collected at different distance from the edge of the main road (2, 10, 30, 40 and 60 meters). In each of the distance, soil samples were collected at three depth (0 - 1 cm, 2 - 4 cm and 4 - 6 cm), by using spiral auger of 2 - 5 cm diameter in all cases, roadside soil samples were place in clean plastic bags and transported to the laboratory.
All roadside soil samples were dried and ground, using a pestle and mortar, to ensure homogeneity; the samples were sieved through 2 mm mesh sieve. The samples were then place in clean plastic bags and sealed pending digestion and analysis.
Two grammes of the oven dried roadside soil samples were weighed into a led washed glass beaker. Soil samples were digested by the addition of 20 cm3 of aqua regia mixture of HCl and HNO3, ratio 3:1) and 10 cm3 of 30% H2O2. The H2O2 was added in small portions to avoid any possible over flow leading to loss of material from the beaker. The beakers were covered with watch glass, and heated over a hot plate at 90˚C for two hours. The beaker wall and watch glass were washed with distilled water and the samples were filtered out to separate the insoluble solid from the supernatant liquid. The volume was adjusted to 100 cm3 with distilled water.
Determination of Cu, Cd, Fe, Pb, As, Mn, Cd and Ni were made directly on each final solution using Perkin— Elmer Analyst 300 Atomic Absorption spectroscopy (AAS).
Standard solution of each sample Cu, Cd, Fe, Pb, As, Mn, Cd and Ni were prepared according to the manufacturer procedure for atomic absorption spectroscopy to be used. Known 1000 mg/L concentration of the metal solution were prepared from their salts.
The pH was measured using 1:2 soil, water ratio [
Data collected were subjected with one-way analysis of variance (ANOVA) to assess whether heavy metals varied significantly between location and distances from the road, possibilities less than 0.05 (p < 0.05) will be considered statistically significant.
The concentrations of some heavy metals with respect to depth and distances from the road within Gboko Road (industrial area) in Benue Metropolis are as presented in
from the road and depth ranged from 1.43 to 18.45 μg/g and Cd concentrations ranged from 1.05 to 16.45 μg/g; 6.54 to 35.11 μg/g Fe; 1.78 to 25.34 μg/g Pb; 1.77 to 19.34 μg/g As; 8.45 to 28.12 μg/g Mn; 20.21 to 61.56 μg/g Zn and 4.34 to 23.23 μg/g Ni. The highest concentrations of all the metals were observed at a distance of 2 meters close to the road and at depth a 4 - 6 cm, while the lowest concentrations were detected at 60 meters away from the road.
The mean concentrations of pH, electrical conductivity (EC), organic carbon and organic matter with respect to depth and distances from the road within Gboko Road (industrial area) in Benue Metropolis are as presented in
It is known that Cu is an essential element, yet it may be toxic to both humans and animals when its concentration exceeds the safe limits, and its concentration in some human tissues such as thyroid can be changed depending on the tissue state. The highest Cu concentration of 44.21 µg/g was detected at Wurukum junction (heavy traffic area), which is located at the major commercial area with high vehicular activities, while the lowest concentration of 3.22 µg/g was observed at the Federal lowcost housing area. The reason for the presence concentrations of Cu in the roadside soil samples might be due to corrosion of metallic parts of cars derived from engine wear, thrust bearing, brushing, and bearing metals [
The concentrations of copper in all the sampling points’ increases with increased in depth. Copper mobility down to 15 cm has been detected in roadside soil by [
[
Cadmium is mostly encountered in cadmium-nickel battery production, although it continues to be used in paints as well as in plastic production where it is an effective stabilizing agent. Occupational exposure to cadmium can occur through metal refining processes, where cadmium is often associated with copper and can be released into the atmosphere during heating. Individuals exposed to cadmium can develop osteoporosis, anemia, eosinophilia, emphysema, and renal tubular damage. Long-term cadmium toxicity can produce Itai-Itai disease, in which individuals suffer from bone fractures, severe pain, proteinuria, and severe osteomalacia [
Iron was found to be the dominant metals as compared with other heavy metals in the roadside soil. Iron is vital for almost all living organisms, participating in a wide variety of metabolic processes, including oxygen transport, DNA synthesis, and electron transport. It is known that adequate iron in a diet is very important for decreasing the incidence of anemia. High concentration of Fe (48.54 µg/g) in the soil samples was observed at the wurunkum junction (heavy traffic area), while Federal Lowcost housing (residential area) shows the lowest value. The variations of Fe in all the sampling points might be due to the differences in traffic density. The possible source of iron in the roadside soil samples might be brake lining material. Results of analysis of variance (ANOVA) confirmed a significant difference in the concentrations of Fe within the sampling points. [
Lead is a nondegradable and toxic element [
The deficiency of manganese in the human body can produce severe skeletal and reproductive abnormalities in mammals. High doses of manganese produce adverse effects primarily on the lungs and on the brain. The highest Mn concentration in the roadside soil samples was observed at the Wurukum junction (heavy traffic area), follow by Gboko road (industrial area), while the lowest Mn concentrations was detected at the Federal lowcost housing (residential area). Results of analysis of variance (ANOVA) confirmed a significant difference in the Mn content within the sampling points. Mn concentrations found in this study are lower than the value of 107 µg/g reported in Aqaba, Jordan [
Zinc, in the roadside soil close to the highway, exhibited elevated levels of all the sampling point studied. The highest Zn concentration of 90.43 µg/g was detected at Wurukum sampling point. The traffic situation in this area of study might be regarded as a source of zinc in the roadside soil. Wear and corrosion of vehicle parts (brakes, tyres, radiators, body and engine parts) might also be one of the potential sources of Zn in this area of study. Zn values in the roadside soil samples from the wurukum and Gboko sampling points were found to be higher than other sampling points. Generally, the major sources of Zn are probably the attrition of motor vehicle tire rubber exacerbated by poor road surfaces, and the lubricating oils in which Zn is found as part of many additives such as zinc dithiophosphates. The concentrations of Zn found in the present study are lower than that of roadside dust samples reported by other literature such as 499.20 mg/kg in Delhi [
Nickel has many common industrial uses due to its unique chemical properties. Industrially, it is used in electroplating, electroforming, in circuitry, and in nickel-cadmium batteries. Metallic nickel is noncarcinogenic to humans; however, all other nickel compounds, such as nickel sulfides, oxides, and silicates, and other soluble salts are known carcinogens. Carcinogenic nickel exposure is greatest through the inhalation of nickel containing particulates. The burning of fossil fuels as well as the refining of metals such as copper introduces considerable amounts of nickel into the atmosphere [
The pH of roadside soil in all the sampling points is in the acidic range. Organic mattervaried from 0.12% to 3.79%; 9.24 to 154.80 µS∙cm−1 and decreases with increased in depth (Figures 5-8). Organic carbonalso increased with depth. The effect of pH on heavy metal availability to plants has been reported by many researchers and it is accepted that as pH decreases, the solubility of cationic forms of metals in the soil solution increases and, therefore, they become more available to plants [
In all the sampling points, Fe and Zn show the highest concentrations in the roadside soil. The concentrations of all the metals in the four sampling sites decreased exponentially with distance from the edge of the road and dropped to the minimum levels at about 60 meters. Similarly, mean concentrations of Cu, Fe, Pb, As, Mn, Zn, Cd and Ni were significantly higher around the industrial area (Gboko road) and heavy traffic area (Wurunkum) than the residential area followed an increasing trend with the increase in depth. From the results of this study, the pH of the roadside soils from all the sampling points ranged from 4.56 to 7.71, which give rise to metal solubility down the soil profiles. The values of the metals in the present study suggest that automobiles and traffic activities are a major source of these metals in the roadside soil. Also, with exception of Pb, Fe and Cd, the levels of Cu, As, Mn, Zn and Ni in the present study were lower as compared with results found by other researcher in various countries worldwide.