Determination of residues concentration and ecotoxicology of organophosphorus pesticides ‎in soil and water of paddy fields of Rudbar County in Guilan province

Since water and soil are important components of the ecosystem ‎and their quality reduction affects the environment and agriculture, it is necessary to determine ‎the effects of pesticides on soil and water resources and determine their residual concentration ‎levels in the land. Agriculture, especially paddy fields, should be controlled and managed. ‎Therefore, the purpose of this study is to determine and evaluate the level of residual ‎concentrations of organophosphate pesticides in soil and water samples of Rudbar County and to ‎investigate their ecotoxicological status.‎

In this study, the multiplicity of 12 stations was determined using a ‎systematic random method in the paddy lands of Rudbar County. In total, 24 samples including ‎‎12 water samples and 12 soil samples were collected. Water sampling was performed in 1-liter ‎dark-colored bottles and soil sampling was performed from the surface layer according to the ‎standard method. All samples were transferred to a laboratory in a freezer containing dry ice. ‎Organophosphate pesticides were measured using the EPA 8041b standard method. All analyzes ‎were performed by gas chromatography with the mass detector in Aria Shimi Sharif Company. To ‎study the ecotoxicological status of pesticides, two databases named National Pesticide ‎Information Center and Pesticide Properties Database were used. The two databases are affiliated ‎with Oregon State University, the US Environmental Protection Agency, and the University of ‎Hertfordshire. Statistical analysis of the data included analysis of variance using one-way ‎ANOVA test, comparison of means using Duncan's test, correlation using Pearson's method, and ‎analysis of principal components using the covariance method.‎

Based on the results, 11 organophosphate pesticides were identified in water and soil ‎samples of Rudbar paddy fields. Ethion in soil and Diazinon in the water had the highest residual ‎concentrations. Sheikh Ali Tues 1 and 2 and Mirzagolband 1 stations with the values of 4.55, ‎‎3.99 and 3.49 ug/kg had the highest amount of Ethion toxin residues in the soil. In addition, ‎Sheikh Ali Tues 2, Mirzagolband 1, and Halimeh-Jan stations with 3.96, 1.71, and 1.68 ug/L, ‎respectively, had the highest amount of Diazinon pesticide in water samples. The results showed ‎that the downstream lands in the area of Imamzadeh-Hashem compared to the upstream lands in ‎Rudbar city have a higher concentration and load of pollution. The mean concentration remaining ‎in soil samples (0.987 ug/kg) was higher than in water samples (0.304 ug/L). Based on the results ‎of pesticides Diazinon, Methyl Parathion, Azinphos Methyl, Malathion, and Ethion in the studied ‎stations showed a significant difference. A comparison of the mean residual concentrations of ‎pesticides with their physicochemical and ecotoxicological properties showed that in terms of ‎potential risk and toxicity for aquatic organisms, the concentrations of BetaMevinephos, ‎Malathion, and Azinphos Methyl pesticides were 0.043, 0.573, and 0.272 ug/kg, respectively. Has ‎been very high, which has put these pesticides in a situation of high and toxic danger to aquatic ‎organisms in the region.‎

Extreme use of pesticides on agricultural land has caused environmental problems. ‎As a result, monitoring and evaluation of pesticide residues in paddy fields are very important ‎because contaminated effluents are discharged directly from rice fields into rivers, depending on ‎several factors. Due to the high levels of residual concentrations of some organophosphate ‎pesticides in the region, it is necessary to hold training courses on farmers' familiarity with the ‎dangers of pesticides to prevent, control, and reduce pollution under the supervision of experts. ‎Also, to fight non-chemically against pests, it is suggested to use the Trichogramma bee in the ‎form of Trichocart to fight the rice stem-eating worm, colored traps, and attractants in paddy ‎fields.‎