Μελέτη της διάσπασης, κατανομής και μεταφοράς των υπολειμμάτων νέων φυτοφαρμάκων σε υδατικά και εδαφικά συστήματα

Abstract

The aim of this study was the study of partition, transport and fate of six selective and widespread pesticides in soil and aqueous systems. Chapter 1. In this chapter some important data about the classification and the behavior of pesticides in the environmental are summarized, as well as the major synthetic reactionMheir chemical reaction, their toxic effect in mammals, their distribution inthe environment and their degradation processes in environmental matrices. Chapter 2. In this chapter some extensive data as chemical, physical and biological properties are being presented regarding the six selective pesticides. That are the herbicides, alachlor, metolachlor and EPTC, the fungicides, chlorothalonil and benalaxyl, and the insecticide pirimiphos methyl. The methodology of the extraction of the 6 pesticides from water and soil samples, is also described. The detection and the determination of pesticides was performed by gas chromatograph with flame thermoionic detector (FTD), or electron capture detector (ECD). The recoveries for the pesticides range from 68,2 % (for chlorothalonil) to 102,1 % (for alachlor) in water samples, and from 76 % (for chlorothalonil) to 105 % (for alachlor) in soil samples. Chapter 3. lathis chapter the stability in a pH range from 4 to 10 of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos methyl in water, was studied. The determined first order kinetics for the hydrolysis show greater stability in all pH range for . alachlor and metolachlor. The fungicide chlorothalonil and the insecticide pirimiphos methyl show the greatest hydrolysis rates in basic solution. The half-life range were for alachlor from 203,8 days (at pH value 4) to 210 days (pH = 10), for metolachlor from 154 days (pH = 7) to 182 days (pH = 10), for EPTC from 154 days (pH = 10) to 330 days (pH = 4), for chlorothalonil from 19,5 days (pH = 10) to 82,5 days (pH = 4) and for pirimiphos methyl from 22,1 days (pH = 10) to 83,5 days (pH = 7). Chapter 4. First characteristic soils with different organic matter content were used to study the adsorption of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos methyl in “ batch experiments”. The adsorption isotherms were described by the Freiindlichequation : x/m = K CeI/n. The isotherms of alachlor and metolachlor seem to fit the S type in all soil types. For chlorothalonil, the adsorption isotherms were S, L and C type as the organic matter in soil increases. EPTC follow the L type in four from the five soil, and C type in the soil with organic matter content of 0,9 %. The isotherms of the insecticide pirimiphos methyl and herbicide EPTC are L type in four soils, and C type in soil with 0,90 % organic matter content. Mass balance estimationsshow that the percent adsorbed amounts of metolachlor, chlorothalonil and pirimiphos methyl increase as the organic matter content increases. The adsorbed amounts were not influenced by the organic matter content for alachlor and EPTC. The adsorbed amount reach 98,4 % for chlorothalonil and 96,3 % for pirimiphos methyl on soil of L Freising (Germany) with 10,4 % organic matter content. Chapter 5. The results of adsorption experiments of alachlor, metolachlor, EPTC,chlorothalonil and pirimiphos methyl on columns soil confirm that, for each compound is following different adsorption mechanism on different soil as compared with the adsorption in aqueous solution (batch method). Generally, mass balance estimations show that the adsorption amount increases with the increase of organic matter content in soil, but this pattern were not followed for all soil types. The higher percentage of cumulative adsorption for all types soil was reported forchlorothalonil, as it is reported also, in “ batch method” . The soils with the higher adsorption capacity were the L-N.Malgara and C-Katsika (Ioannina). The total removed amounts (%) of pesticides on the five characteristic soils, ranged from 8,1 % for EPTC on soil L-Freising (Germany) to 56,2 % for pirimiphos methyl on soil L-N.Malgara. The overall results showed that the removed amounts (%) of five pesticides on soil columns were lower as compared with the batch experiments. The above results could be explained considering the smaller soil/solution ration and the smaller experimental time, in the column experiments. Chapter 6. In this chapter the runoff losses of the herbicides of alachlor, metolachlor and EPTG, were studied in relation to the soil surface slope. Sandy-clay-loam soil plots cultivated with com were tested for a period of one year. The surface slope of plots was 0, 1, 2.5 and 5 % and the soil erosion was increased with the slope from 47 2 2 g/m to 135 g/m . The gradual disappearance of the above herbicide residues fromfield soil under natural cultivation conditions as a function of time is described by first order kinetic, as it is expressed by the equation C = CQ exp(-kt). With further processing of the results it was possible to study the effect of slope and cultivation on the half time (t>/2) of these compounds. There is a gradual drop in the concentration of the three herbicides detected in the soil as a fiinction of time, but it is not the case for the soil sampling that follows after the second application ofherbicides on the 9th July 1997. The rate of decrement is accelerated in the field plots planted with com as compared to untilled plots. The decomposition and disappearance of the herbicides further accelerates in soil plots with larger slopes and the half -life times depend on the compound physicochemical properties. Quantification of the disappearance rates indicates that com plantation decreased the half-life time of herbicides as compared to the control fields, as follows: -alachlor - from 16.7 to 10 days, - metolachlor - from 22.3 to 13.3 days and - EPTC - from 17.8 to 8 days.The total losses of the three herbicides in surface runoff in untilled plots was much higher than the corresponding tilled plots with smaller slope. Finally, the overall results under natural rainfall and irrigation conditions indicated that the movement of alachlor, metolachlor and EPTC in surface runoff, was limited. The highest percentage loss was observed for metolachlor (1.088% for a slope5% in untilled plot). Chapter 7. The losses on runoff surface of insecticide pirimiphos methyl and fungicide benalaxyl, was determided with the above method as already described, on sandy-rclay-loam soil plots cultivated with potatoes in relation with the soil surface slope, for a period of one year. The surface slopes of plots was 0, 1, 2.5 and 5 % and the 2 2 soil erosion was increased with the slope from a value 45 g/m to 176 g/m . The loss of pirimiphos methyl and benalaxyl from tilled and untilled soil follow first order kinetics, C = Co. exp(-kt). There is a gradual drop in the concentration of the two pesticides detected in the soil as a function of time, but it is not the case for the soil sampling that follows after the second application of herbicides on the 24th October 1998. The rate of decrement is accelerated in the fields plots planted with potatoes as compared to unfilled plots, and the highest values were observed for pirimiphos methyl. Quantification of the disappearance rates indicates that potatoes plantation decreased the half-life time of both pesticides as compared to the control fields as follows: -pirimiphos methyl - from 16,7 to 9,2 days and -benalaxyl - from 26,7.9 to 12.6 days. The total losses of the pirimiphos methyl in surface runoff in untilled plots was much higher than the corresponding tilled with smaller slope. On the contrary, the total losses of benalaxyl were in same levels. Finally the overall results under natural rainfall indicated that the movement of pirimiphos-methyl and benalaxyl in surface runoff, was limmited. The highest percentage loss was observed for benalaxyl (1.75 % for a slope 5%'in unfilled plot).