DISTRIBUTION OF PERSISTENT ORGANIC POLLUTANTS IN SOIL WITHIN AND AROUND ONDO STATE WASTE MANAGEMENT SITE, IGBATORO ROAD, AKURE

Abstract

Soil as a key component of the environment serves as a storage medium for resources. However, it also accumulates pollutants that are not easily degraded by nature and for that reason become persistent. Soil samples from within and around the Ondo State Waste Management site were characterized for physicochemical properties, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) with the aim of assessing the level of contamination of the site and the toxicity potential of these persistent organic pollutants (POPs). Sixteen (16) samples were collected at a depth of about 0-15 cm using stainless steel auger. Extraction and clean-up were done using USEPA Ultrasonic Method 3550C and USEPA Silica gel clean-up Method 3630C respectively, while identification and quantification of PAHs and OCPs were carried out using Gas Chromatograph coupled with Mass Spectrometer (GC-MS) and Gas Chromatograph with Electron Capture Detector (GC-ECD), respectively. The study showed that the individual PAH concentration ranged between 0.0002 to 0.3294 μg/kg while the total polycyclic aromatic hydrocarbons (TPAH) concentrations and average PAH concentrations ranged from 0.05-1.28 μg/kg and 0.003-0.071 μg/kg respectively. Analysis showed weak positive correlation between TPAH and total organic carbon, pH and percentage sand. The more hydrophobic high molecular weight PAHs dominate the site with 56% abundance compared to low molecular weight PAHs with 44% abundance. PAHs with carcinogenic potential constitute 35.50% of the total PAH concentration across all samples. The total concentration of carcinogenic PAHs across the samples ranged from 0.0021 μg/kg - 0.1651 μg/kg. The study further revealed that among the eight possible human carcinogens, benzo(a)pyrene (0.2161), benzo(k)fluoranthene (0.017) and benzo(b)fluoranthene (0.015), are the most toxic and have the highest potential to cause carcinogenic effects. Organochlorine pesticides concentrations on the other hand ranged from 0.05 μg/kg to 174.905 μg/kg while total organochlorine concentration ranged from 2.352 μg/kg (sample E 1 ) to 338.695 μg/kg (sample N 4 ). The total organochlorine concentrations exhibited a weak positive correlation with organic carbon (R 2 = 0.0073) and across all the samples taken from site and its environs, alpha-cypermethrin and beta-cypermethrin were the most abundant with the concentrations of 174.905 μg/kg and 140.645 μg/kg respectively. The total PAH concentration and the concentrations of the organochlorine pesticides when compared with the European Classification of Soil Contamination (based on 16 PAHs) USEPA priority pollutants and United Nations Food and Agricultural Organization maximum permissible concentrations of organochlorine pesticides in contaminated soil respectively, revealed that this site is not polluted. However, the site is contaminated with these substances. Even though the concentrations of the PAHs and organochlorines are low, they have the potential to cause divers negative effect if allowed to accumulate over time. Therefore, the management of this waste site should ensure the deployment of modern waste management technology in the treatment and disposal, while a remedial plan should be developed for the site and its surroundings.