دانلود رایگان مقاله انگلیسی ارزیابی ارگانوکلره باقیمانده سموم در آب و رسوبات - نشریه الزویر

Abstract

In this study, the levels of organochlorine (OC) pesticide residues in Lake Tashk have been investigated using water, sediment and fish (carp) samples as a case study to find out the extent of pesticide contamination and accumulation in the lake. Six OC pesticides namely DDT, DDE, lindane, endosulfan, heptachlor and chlordane were analyzed in four sites at four seasons. Water samples were processed using a liquid–liquid extraction technique and gas chromatograph equipped with electron capture detector (GC-ECD). Soxhlet extraction was used for fish and sediment samples followed by clean up and gas chromatograph. DDE was the predominant residue in all the samples analyzed, at the mean concentrations of 0.075 ppb, 8.750 ppb and 4.446 ppb in water, sediment and fish samples, respectively. The lowest levels of OC pesticides were related to heptachlor and chlordane which none of them were found in water samples. Gonban and Midstream sites had the highest and the lowest concentrations of OC pesticides, respectively.

Results and Discussion

Lake Tashk is surrounded by farm lands. A large amount of chemicals (fertilizers and pesticides) are used there by farmers which can enter the wetland through running waters and subterranean canals. Also, garbage and wastewaters are poured in the wetland by inhabitants. All of these factors may lead to the contamination of Lake Tashk. Results from the study have been shown in Tables 1, 2 and 3 which are related to the concentration of OC residues in water, sediment and fish samples, respectively. DDT was detected in 43% of water samples, 72% of sediments and 88% of fish samples. The associated figures for mean concentrations were 0.028 ppb, 5.22 ppb and 4.218 ppb. The ratios of incidence as well as the concentrations of DDE, a metabolite of DDT, in all the three sample types were higher than those recorded for DDT which was 87%, 94%, 92% in water, sediment and fish samples, respectively. This observed trend could be attributed to the decomposition and bioaccumulation of the DDT used in the past. DDE is more stable than DDT and decomposes more slowly by micro-organisms, heat and ultraviolet rays (Esmaili Sari, 2002)