Assessment of Heavy Metals, pH, Organic Matter and Organic Carbon in Roadside Soils in Makurdi Metropolis, Benue State, Nigeria

Abstract

Roadside soil samples were collected from four sites (heavy traffic area (Wurukum); industrial site (Gboko road); residential area (Federal Lowcost) and Federal Medical Center (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 cm and 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 depth 6 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.

Spatial Distribution of Heavy Metals in the Surface Sediments of the Southern Coast of Pacitan, Indonesia

“…Although there might be no exact point source of cadmium in the study areas (as shown by the lower concentration of cadmium compared to the other heavy metal concentrations), cadmium input might come from the pollution of cadmium from the air. Cadmium can be released into the atmosphere during heating in metal refining processes in association with copper [8]. Unlike the distribution of Pb that is related to lower pH, higher Cd concentrations might be related to the increased value of pH.…”

“…Higher concentration of Pb at Pantai Watu Karung and Pantai Soge compared to the concentration at Pantai Teleng Ria and Pantai Pancer clearly showed the effect of lower pH value especially at Pantai Watu Karung (pH = 7.92). Based on the experimental study on the effect of pH on metal release and sequestration [8], it was found that found a high concentration of Pb in the low-pH experiments. This metal showed little or no release from the sediment for the high-and mid-pH experiments.…”

“…Dissolved oxygen can influence the release of heavy metals from sediment by affecting the rate of oxidation of organic compound [7]. It has been understood that organic matter plays an important role in metal binding [8] and the oxidation rate of organic matter is higher in the aerobic condition [7]. Low concentration of heavy metals in the surface sediments in this study might be related to high concentration of DO that easily released metals from the sediment to the overlying waters due to the binding of heavy metals with organic matter.…”

“…Moreover, pH controls the adsorption and precipitation process of heavy metals in the sediment [7]. A low pH value or acidic environment increases heavy metal concentrations because heavy metals are generally more mobile when pH is less than 7 [8]. In addition, heavy metal concentrations have a significant correlation with organic matter content as dissolved and particulate organic matter can act as a scavenger for metals that accumulate in bottom sediment [1,9].…”

Influence of Land Use on the Content of Select Forms of Cd, Cr, Cu, Ni, Pb, and Zn in Urban Soils

“…In general, alkaline reaction reduces mobility of some heavy metals and contributes to their accumulation in different soil horizons [26,27]. For this reason, the highest concentrations of heavy metals are often not found in nearsurface horizons.…”