Hossein Banejad; H. Banejad; F. Mohsenzadeh
Abstract
Introduction: Pesticides are considered as the most important pollutants in surface water and groundwater. Neonicotinoids are new group of insecticides, derived from nicotine. Their physicochemical properties render them useful for a wide range of application techniques, including foliar, seed treatment, ...
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Introduction: Pesticides are considered as the most important pollutants in surface water and groundwater. Neonicotinoids are new group of insecticides, derived from nicotine. Their physicochemical properties render them useful for a wide range of application techniques, including foliar, seed treatment, soil drench and stem applications. Confidor, the representative of the first generation of neonicotinoid insecticides, was patented in 1985 by Bayer and was placed on the market in 1991. The Canadian Pest Management Regulatory Agency considers confidor to have high potential for surface water contamination, leaching to groundwater and persistence in soils. Biodegradation is one of the most effective ways to destroy pesticides in the environment. The application of Bioremediation techniques is taken into consideration as an option to reduce or remove pollutants from the environment due to their low cost, high efficiency and environmentally friendly features. Bioremediation by using microorganisms has not any adverse effect after cleanup. The accumulator microorganism species, haven’t pathogenic properties and aren’t the cause of disease on the other organisms. The selection of a biomass for using in bioremediation is very important, it should be abundant in environment and adapted to environmental conditions. The aim of this study was to investigate the ability of various species of Trichoderma fungi to remove Confidor from contaminated water influenced by variables like pH, concentration of the confidor and time.
Materials and Methods: In order to conduct this study three different fungal species belonging to the genus Trichoderma were used. The samples were transferred to PDA (Potato Dextrose Agar) sterile solid media for in vitro testing usage. The samples were kept in refrigerator at 4◦C temperature, after the fungal biomass reached to maximal growth; the colonies were transferred to new media and used in our experiments as resources. After complete fungal growth on the solid media, liquid media were prepared with the formula containing 250 g/l potato extract, 20 g/l dextrose and 0.25 g/l Tetracycline antibiotic (to prevent bacteria growth) in three pH (5,7,9) and three toxicant concentrations (1, 3 and 5 mg/l). Lactic acid and KOH (3%) were used to adjust pH in the prepared media. The degradation experiments were performed in a 50 ml falcon for 1 month. All experiments were maintained under similar conditions. The samples were shacken daily. After 1 month of incubation, aliquots (2 ml) were removed; centrifuged and the supernatants were used for the estimation of concentration of residual confidor by spectrophotometer. The results were analyzed by SPSS software.
Results and Discussion: According to the results T.harzianum with 60.34% confidor removal had the highest ability and T.tomentosum with 44.60% had the lowest ability to biological degradation of confidor from the polluted waters. The maximum confidor removal (75.89%) using T.harzianum was accrued to acidic media with 5 mg/l of confidor. The minimum confidor removal (53.09%) using T.asperellum was accrued to alkaline media with 1 mg/l of confidor. Using T.tomentosum the efficiency of confidor removal in media with pH=5 and concentration of 5 mg/l was increased by 10.95% and 15.63% compared to the environments with the concentrations of 3 and 1 mg/l, respectively. In the media containing T.harzianum, the percentage of confidor removal after 4 weeks was increased by 46.21% Compared to the first week. In the media containing T.harzianum, T.asperellum and T.tomentosum, the percentage of confidor removal after 4 weeks was increased by 46.21%, 37.06% and 32.84% respectively, Compared to the first week. Totally, the results showed that all the fungi species are capable to remove confodor. Toxicant concentration increasing from 1 mg/l to 5 mg/l, results in increasing the percentage of toxicant removal. The results of confidor removal from mediums with different pH demonstrated that in all studied fungi, toxicant removal at pH=5 is higher than other pH. The results obtained from this study confirm the hypothesis of positive effect of passing the time on confidor removal efficiency by different Trichoderma species.
Conclusions: In general, we can conclude that three species of studied Trichoderma in this research can be applied for bioremediation of agricultural waters which are contaminated by confidor. As a result, by collecting the agricultural water that are contaminated with confider and application of these fungi as biological purifiers, we will access to a considerable amount of non-conventional water resources to irrigate of downstream. It is noteworthy that Trichoderma species in addition to the biorefinery potential of pollutants , are able to improve soil structure and increase plant resistance.
