Investigation of oil and grease in surface soils of gas station, automobile repair workshop, urban, recreational area, and rural sites using FT-IR

The principal objective of this study is to examine the oil and grease (OG) content in surface soil samples using Fourier transform infrared (FT-IR) spectroscopy. The standard solution is a mixture of isooctane and octanoic acid (1:1 by weight) in tetrachloroethylene. The linear working range was established to be between 25 and 350 ppm. The limit of detection (LOD) was determined to be 2.36 ppm, while the limit of quantification (LOQ) was calculated to be 7.87 ppm. The mean recovery value of OG exhibited a range of 82.75% to 93.75% in surface soil samples. To assess the precision and accuracy of the method, standard addition experiments were conducted by spiking the isooctane and octanoic acid mixture, and the resulting spiked samples were analyzed in triplicate. After the completion of the validation studies, the concentrations of OG were determined in surface soil samples collected from regions hypothesized to have varying levels of pollution accumulation. These sampling sites included recreational areas, urban areas, rural areas, locations adjacent to gas stations, and areas near industrial sites. The determined OG concentrations are 15.9 ± 4.57, 6.9 ± 2.02, 2.4 ± 0.93, 14.9 ± 1.71, and 10.1 ± 1.16 µg/g dry weight (dw), respectively. Due to possible barbecue activities and other anthropogenic effects, the highest concentration of oil and grease was observed in the sample of the recreational area. The second highest concentration was found in gas station samples, likely due to heavy traffic and the gas station itself, while the lowest concentration was observed in the rural area, as expected due to the lack of potential pollution sources next to the sampling site. These findings indicate potential environmental risks in areas with high human activity and traffic, highlighting the need for remediation efforts. Also, the method of OG determination using infrared spectroscopy offers a more expedient, cost-effective, and environmentally friendly approach for the analysis of soil samples, particularly due to the minimal use of chemicals. Also, the method of oil and grease determination using infrared spectroscopy offers a more expedient, cost-effective, and environmentally friendly approach for the analysis of soil samples, particularly due to the minimal use of chemicals.