This study employed turbidimetric method using a UV/VIS spectrophotometer to determine the total sulfur levels of refined petroleum products in Southwestern Nigeria. The sulfur concentrations in the analyzed fuel samples were 0.0019-0.0178 wt% and 0.027-0.169 wt% for gasoline and diesel, respectively. Sulfur levels in the selected samples were below the Nigerian standard for gasoline and diesel while 89.9% of the samples exceeded the U.S. Environmental Protection Agency standard. The turbidimetric method showed better performance than the gravimetric method. The results gave insight into the adverse environmental impact the nonuniform quality of fuels imported could pose to the country.

Background. Rare earth element (REE) composition of atmospheric dust has recently been used to trace potential sources of dust pollution. Objective. The present study aimed to determine the sources of atmospheric pollution in the study area using REE patterns and determine their level of pollution. Methods. Twenty-five (25) atmospheric dust samples were collected in the study area, with five samples each from an industrial area, traffic area, dumpsite area, residential area and remote area in Ibadan, southwestern Nigeria. In addition, five (5) topsoil and two (2) rock samples (granite gneiss) were collected for comparison. Concentrations of REE were determined by inductively coupled plasma mass spectrometry (ICP-MS). Results. The ratio of lanthanum/cerium (La/Ce), especially in some locations in industrial area (1.5), traffic area (1.5) and to some extent dumpsite area (1.1) was higher than in soil (0.2), upper continental crust (0.5) and the minimum value of fluid catalytic crackers (1.0). Generally, the respective average values of the ratios of La/praseodymium (Pr), La/neodymium (Nd) and La/samarium (Sm) in industrial area (32.1, 7.8 and 52.6) and traffic area (14.9, 4.4 and 26.8) were higher than their respective averages in soil (4.4, 1.1 and 6.2), rock (5.7, 1.9 and 14.1), upper continental crust (4.4, 1.1 and 6.6) and the minimum value in fluid catalytic crackers (5.8, 3.7 and 37.0). Meanwhile, their corresponding value in the dumpsite area, residential area and remote area were lower or similar to the geological background levels. Discussion. The contamination factors of REEs in the atmospheric dust of the industrial area and traffic area were classified as heavily contaminated, especially with light lanthanoid elements in REE. The degree of contamination of REEs in the atmospheric dust of industrial area (30.9) and traffic area (18.8) fell within the considerable contamination category. The high values of the light lanthanoid ratio and the contamination indices were attributed to their emission from the fired-power plant and vehicular exhaust. Conclusions. Most of the composition of the atmospheric dust was sourced from the local geology of the study area as observed in the residential area and remote area, while the contamination in the industrial area and traffic area was attributed to human activities. Competing Interests. The authors declare no competing financial interests.

Potentially Toxic Elements (PTE) contaminated soils within urban areas have received global attention. However, little attention is being given to soils of suburban areas, which are also vulnerable to PTE contamination from both natural and unnatural sources. This study was conducted to determine soil quality and PTE pollution sources in soils of Apomu, Southwestern Nigeria. The concentration of PTEs was determined by subjecting soils to elemental analysis using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Pollution indices and health risks were calculated. The results showed the following range of metal concentrations in ppm except for Al (%) in increasing order; Mo (0.58-12.29), Cu (16.65-687.47), Pb (28.64-368.75), Zn (0-9257.30), Ni (7.60-86.20), Mn (403-1756), Cr (26.40-107), Cd (0.20-11.34), and Fe (1.23-4.29). Geoaccumulation Index (Igeo) showed that Zn, Pb, Ni and Cu and moderately contaminated with Cd. The Enrichment Factor (EF) revealed minimal to very high enrichment of Cu and Zn; minimal to significant enrichment of Pb and As and a minimal to moderate enrichment of Ni and Co. The geochemical evaluation revealed that soils were heavily contaminated with PTEs which were sourced from geogenic and anthropogenic activities. Approximately 70% of sampling areas exhib[1]ited high potential ecological concerns. The hazard index (HI) values for children and adults were less than one (HI < 1), indicating that there was no major danger of poisoning. Carcinogenic risks for Cd, Ni, and Pb were calculated and found to be within tolerable limits, but children are more susceptible to cancer and non-cancer risks than adults.