Levels of Organochlorine Pesticides and Potentially Toxic Metals in Soil, Crops and Aquatic Ecosystem of Esa-Oke Farm Settlement, Osun State, Nigeria
This study was conducted on seasonal basis to evaluate levels of physicochemical parameters, organochlorine pesticides (OCPs) and potentially toxic metals (PTMs) in crop, soil, water, sediment and fish samples of Esa-Oke farm settlement. It also evaluated the health risk indices (HRi) of the xenobiotics investigated in water and food items. This was done with a view to determining the pollution status and the health effect that the consumers of the produce from the farm settlement could be exposed to. Sampling of soil, water, sediments, four types of food crops (yam, cocoyam, sweet potatoes and cassava) and two fish samples of the same species (Tilapia zillii) were done within the Farm Settlement at six specified sites from six different locations in four months each during the dry and wet seasons. Applicable physicochemical parameters of the samples were determined using the American Public Health Association (APHA) standard methods. Microwave digestion method was used for wet digestion of the samples for total potentially toxic metals determination. Metal speciation was carried out using an optimized and established method while OCP recidues were extracted using Soxhlet extraction kit with dichloromethane as the solvent. Identification and estimation of OCPs in extracts of crops, water, fish and sediment samples, after clean-up on silica gel adsorbent, were carried out using Gas Chromatography equipped with Time-of-Flight Mass Spectroscopy Detector (GC - GCToFMS). Higher levels of PTMs were recorded in sediments during wet season (0.13 ± 0.14 to 304.90 ± 54.30 mg/kg) than dry season (0.20 ± 0.03 to 268.60 ± 63.79 mg/kg). The levels of metals in fish tissues ranged from 11.00 mg/kg (bone) to 118.30 mg/kg (intestine) in wet season, while in dry season the range was 16.69 mg/kg (bone) to 194.94 mg/kg (intestine). The seasonal variations of PTMs concentrations (mg/kg) in soil for both seasons gave a range of 0.14 mg/kg Cd to Fe 224.20 mg/kg Fe. The overall seasonal mean levels of OCPs in crop samples ranged from 173.73 mg/kg (aldrin) to 550.29 mg/kg (o,p’ – DDE). The seasonal overall mean values of OCPs in sediment samples gave 647.29 mg/kg during wet season and 551.30 mg/kg in dry season. The total seasonal mean value of OCPs in fish samples was higher in wet season (21.51 mg/kg) than dry season (12.29 mg/kg). However, the overall mean seaonsal values of (6.23 mg/L) OCPs in water samples was higher in dry season than wet season (2.85 mg/L). The study concluded that regular consumption of crop products from the farm settlement could result in grave public health concern overtime because the estimated daily intake (EDI) for PTMs values were above RfD value in crop samples and levels of OCPs obtained in water and food crops from Esa-Oke Farm Settlement were gave cause for environmental and health concerns.