Abstract:
In this study, the levels of some selected organophosphorous (OPPs) and organochlorine pesticides (OCPs) in water samples collected from Gilgle Gibe (I) hydroelectric dam and potential tributaries, Jimma zone, Oromia Regional State, Ethiopia were determined using gas chromatography electron capture detector (GC–ECD). Low density based dispersive liquid-liquid microextraction (LD-DLLME) using toluene (as extractant) and acetonitrile (as disperser) was used for extraction of the pesticides from water samples. Calibration curves were constructed at six concentration points by spiking and extracting distilled water a representative matrix. And the obtained calibration curves have good linearity with coefficient of determination (r 2 ), ranging from 0.995-0.999. The limits of detection (LOD) and quantification (LOQ) of the utilized method which were determined as 3 and 10 times the signal-to-noise ratio were ranging from 0.0001-2.5810 µg/L and 0.0005-8.6050 µg/L, respectively. The efficiency of the methods was also evaluated through recovery studies by spiking the samples with known concentrations of the target analytes. The obtained recoveries were ranging from 67.2-105% with 0.79 - 12.5% relative standard deviations. The study results demonstrated that all water samples contain the target pesticides. But endrin was not detected in all the water samples. Methidathion was also not detected in the dam, as well as Nadi and Gibe river samples. The detected residual concentrations of the pesticides were all above the maximum residue limits, with the exception of DDT in acute toxic level. Results of the study indicated the studied water samples contain considerable amount of residues of pesticides that can influence the health of aquatic organisms and other consumers.
