MATERIALS AND METHODS
1.Fish, sediment and water samples were obtained from four various sites namely Gadarzavali, Hellak, Pol-e Abgineh and Midstream in Lake Parishan.
2.Samplings were conducted seasonally from winter 2010 to autumn 2010 following US-EPA [15].
3.Samples were collected from surface parts of the water and sediment.
4.Also, each sampling was carried out in three replicates.
5.A total of 48 samples each of sediments and water were collected randomly.
6.However, fish samples were 14 because of little rainfall in recent years which has caused a decrease in water depth leading to limited dispersal of fish species.
7.All samples collected (water, sediments and fish) were immediately stored in an ice-chest at 4°C and transported to the laboratory for analysis.
Extraction of OC Pesticides in Water Samples:
1.In the laboratory, using liquid-liquid extraction (LLE) as described in APHA [16], the total amount of each surface water sample (800 ml) was filtered with Whatman filter paper (i.d. 70 mm) to remove debris and suspended materials and then poured into a 2 liter separatory funnel.
2.For the first LLE, the mixture of 100 ml n-hexane and dichloromethane (1:1 v/v) was added and shaken vigorously for 2 min before two phase separation.
3.The water-phase was drained from the separatory funnel into a 1000 ml beaker.
4.The organic-phase was carefully poured into a glass funnel containing 20 g of anhydrous sodium sulfate through a 200 ml concentrator tube.
5.Following the second and third LLE, the water-phase was poured back into the separatory funnel to re-extract with 50 ml of the same solvent mixture.
6.The extract was concentrated to the volume of 2 ml under a gentle stream of nitrogen using rotary evaporator and then analyzed with Gas Chromatography with micro Electron Capture Detector (GC-ìECD) [17].
Extraction of OC Pesticides in Fish and Sediment Samples:
1.The muscle tissues of the fish samples were ground in a blender to obtain a homogenous composite, ground in a blender to obtain a homogenous composite,
2.OC residues in sediments and fish samples were extracted using Soxhlet Extraction [18].
3.A 10 g sample was placed into a beaker containing 50 g anhydrous sodium sulfate and mixed thoroughly.
4.The sample mixture was transferred to an extraction thimble and placed in a Soxhlet extractor.
5.The mixture was extracted with 150 ml of acetone: n-hexane (20:80 v/v) at 50°C for 4 h.
6.The extracts were filtered,concentrated to 1 ml using vacuum rotary evaporator.
7.Each of the raw extracts was then dissolved in 10 ml hexane and passed through pre-conditioned octadecyl C-18 columns at a rate of 2 ml minG to clean up.
8.The column was washed with 1 ml, 30% methanol followed by 1 ml ultrapure water and was allowed to dry.
9.The sample (analyte) which was trapped in the column was eluted 5 times with 0.5 ml aliquots of hexane to recover the pesticide residues.
10.Hexane in the sample was then allowed to evaporate off leaving the residue alone in the vial.
11.Dried sample was dissolved in 1 ml portion of hexane, mixed thoroughly with a whirl mixer and then transferred to auto sampler vials ready for gas chromatography [5].
12.Statistical analyses were carried out by analysis of variance (ANOVA) using SPSS 15 software.
13. Mean values were analyzed by the Duncan’s test.