Risk Assessment of Dichlorodiphenyltrichloroethane Residues in Soil and Rice Samples Harvested in Selected Rice Farms of Benue State, Nigeria

Abstract

This work investigates the level of Dichlorodiphenyltrichloroethane (DDT) residues in soil and rice samples collected from Otukpo farmland area of Benue State. Ten soil samples and five different species of rice samples were collected from the farmlands to determine the concentration of DDT residues. Standard analytical methods were employed for the determination of some physicochemical parameters (pH, total organic carbon, moisture content and cation exchange capacity) of the samples. Collected samples were analyzed for residues of total dichlorodiphenyltrichloroethane using gas chromatography mass spectrometry (GC-MS) after careful extraction and cleanup. Risk assessment was carried out by determining the hazard indices. The results of the physicochemical analysis showed that the mean pH value of soil samples is 6.2 indicating slight acidity as compared to rice 7.34 which is approximately neutral and within WHO acceptable limits. The mean total organic carbon (TOC) value is 14.57% while the mean cation exchange capacity is 7.85 meq/100g in soil. DDT was detected with average concentration of 10.5 mg/kg in soil and 3.41 mg/kg in rice which is above the EU/WHO and MRL recommended rate of 0.1 mg/kg and 0.05 mg/kg. Harzard indices employed in this research shows that rice species are fit for consumption with the exception of those with Hazard Index level greater than one in children. The contamination levels of DDT in the analyzed soil based on national standards are considered toxic for crop production but analysis shows that the uptake level of DDT from soil to crop is very low which makes the rice cultivaled fit for consumption.