Effect of vegetable oil on the degradation of a pesticide mixture in biobeds

Sammanfattning: Pesticides are used to control diseases, undesired vegetation and insects in forestry, gardening and agriculture. In the environment, pesticides are generally believed to originate from a diffuse source, such as spray drift of pesticides during application, or a point source, such as spills during refill and cleaning of spraying equipment. Point sources are easier to eliminate than diffuse sources and one method to reduce the leaching from point sources is to use biobeds as bioprophylaxis. The Swedish biobed was developed by Torstensson and Castillo in 199X (KB) and is constructed with locally available constituents, such as peat, wheat straw and soil. The main advantages of the biobed is that it is very simple and cheap, but still very effective. On sites where vegetable oil have been spilled on the biobed, e.g on farms producing rapeseed oil, both increased activity of lignin degrading microorganisms and increased pesticide degradation have been observed. The lignin degrading microorganisms produce unspecific extracellular enzymes, which also are able to degrade recalcitrant molecules such as organic pollutants. The most important ligninolytic enzymes, currently known, are lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase. Pure MnP have been found to be able to initiate lipid peroxidation. Due to recent findings that vegetable oil, which has high levels of unsaturated fatty acids, is increasing the effect of lignin degrading microorganisms, addition of oil is proposed to further increase the biobed efficiency. Since the crop is determining which pesticide to be used, pesticides are often encountered in mixtures in the environment. For this purpose five selected pesticides will represent the mixture of pesticides. The selected pesticides are bentazone (BZ), metabenzthiazuron (MBTZ), isoproturon (IP), terbutylazine (TBA) and chlorpyrifos (CLP). The main objectives of this study were: I. To investigate whether the addition of rapeseed oil to the biomix (mixture of peat, soil and straw used in a biobed) enhanced the degradation rate of pesticides (BZ, MBTZ, IP, TBA and CLP). II. To investigate whether a potential increase in degradation, of the same pesticide mixture, was explained by a MnP-mediated lipid peroxidation process. The experiment was set up to study whether the addition of oil can have a positive effect on degradation of a mixture of pesticides in a biomix and in soil. Enzymatic activity and microbial respiration were followed during the incubation period. The degradation of the pesticides by pure MnP in the presence of oil was tested in vitro. The experiment was prepared for each pesticide separate and a control without any pesticide added, in total six experimental setups. The main results from these studies are summarized below: • The effect from the addition of oil varies from promoting degradation to inhibiting degradation depending on pesticide. The lack of correlation with phenoloxidase activity could indicate that degradation mechanisms other than ligninolytic enzymes were prevailing or even dominant in this study. • The microbial respiration was higher in biomix than in soils. The addition of oil had an inhibitory effect in the biomix. • The phenoloxidase activity was higher in the biomix compared to the soil. The addition of oil did not increase the enzymatic activity. • In the in vitro experiments the addition of oil enhanced the degradation of IP by MnP, but no positive effect was observed for CLP, TBA, BZ and MBTZ. However, no enhancement of IP degradation was obtained in the biomix in the presence of rapeseed oil. • The initial method for the HPLC analysis was developed so all five pesticides could be detected within a reasonable time frame. However, with the oil-fractions peaking around MTBZ and BZ, and the fact that CLP had to be analysed separately, a new method also for the other four pesticides need to be developed for further studies. The new method for the four pesticides should separate the peaks around BZ and MBTZ further and not take CLP into account. • The interference peak in the chromatograms which increased over the incubation time could a product from vegetable oil being degraded in presence of of MnP could possibly indicate lipid.