제주도 대표토양에서 Lysimeter를 이용한 농약의 용탈

Abstract

Jeju Island uses groundwater as a main water source. It is very important to keep that source from the pesticides applied in agricultural farming. Less vulnerable pesticides should be selected to protect the water sources. So we measured the leaching fraction(C/C0) of the pesticides applied on the farm field using the lysimeters with representative soils of Jeju Island. Several simple indices like RF(retardation factor), AF(attenuation factor) were adapted to explain the fraction(C/C0). Three soil series of Donghong, Jeju, and Pyungdae which were different in both organic matter and color were chosen to fill nine of the wick lysimeters for triplicates to each soil, respectively. On them four fungicides of etridiazole, fluazinam, tebuconazole, tolclofos-methyl, four insecticides of ethoprophos, carbofuran, cypermethrin, fenpropathrin and three herbicides of alachlor, napropamide, pendimethalin were applied to receive the leached water and analyse the fraction. The three soil series used in adsorption experiments showed the organic carbon contents of 1.48 ∼ 13.7%, bulk density of 0.6 ∼ 1.1 g cm3, porosity of 54.4 ∼ 74.4%, hydraulic conductivity of 0.021 ~ 0.059 m day-1, which implied the most properties of representative soils of Jeju island. Of those 11 pesticides, alachlor was the lowest adsorption coefficients(Kd) on soils of 1.2 ∼ 8.5 L kg-1, followed by ethoprophos of 1.8 ∼ 10.5 L kg-1, carbofuran of 2.7 ∼ 17.6 L kg-1, napropamide of 4.7 ∼ 47.2 L kg-1, tebuconazole of 5.9 ∼ 45.5 L kg-1, etridiazole of 9.3 ∼ 78.6 L kg-1, tolclofos-methyl of 26.0 ∼ 223.7 L kg-1, fenpropathrin of 40.0 ∼ 362.9 L kg-1, pendimethalin of 59.5 ∼ 406.1 L kg-1, fluazinam of 142.0 ∼ 789.4 L kg-1 and cypermethrin of 790 ∼ 4,231 L kg-1. Based on leaching criteria of Kd 10 L kg-1 in European countries, alachlor was classified to be vulnerable, but others of ethoprophos, carbofuran, napropamide, tebuconazole and etridiazole showed big difference with soil organic matter. For a group of alachlor, ethoprophos, carbofuran, tebuconazole, napropamide, and etridiazole, which were classified to be vulnerable to groundwater, the values of Kd increased in 0.59, 0.73, 1.27, 3.21, 3.43 and 5.81 with soil organic matter. That means the stronger affinity for each soil resulted in reducing mobility of the pesticides. On the other hand, for another group of tolclofos-methyl, fenpropathrin, pendimethalin, fluazinam and cypermethrin which were classified non-vulnerable, the affinity had the values of 16.5, 26.0, 28.0, 50.6 and 288.0, which showed a big difference from the previous pesticides. Under these results, wick lysimeters were used to measure the actual leaching fraction out of soil profile of 30cm with 50mm rainfall at the interval of 1 week for 9 weeks. The largest fraction from three soils of Donghong, Jeju, and Pyungdae, respectively were carbofuran of 0.10, 0.05, 0.002, followed by alachlor of 0.06, 0.008, 0, ethoprophos of 0.04, 0.002, 0, napropamide of 0.003, 0, 0, tebuconazole of 0.001, 0, 0, which were less leached with the less affinity. The other six ones, however, had no leaching, which all had the water solubility of 1.0 mg L-1 less as well. Etridiazole which was classified vulnerable based on Kd value of 9.3 L kg-1 was not leached in lysimeter experiment. This was estimated to be due to the strong affinity of 5.8, which is twice that of the other vulnerable ones, as well as vapor pressure of 1,430mPa, although it has the water solubility of 89mg L-1. On the other hand, the non-vulnerable pesticides were less soluble than 0.71 mg L-1. Pyungdae soil series with large organic matter also had the Kd of 8.5 L kg-1 for alachlor, meaning it is mobile, but hadn't leached during the study. On the contrary, for the carbofuran which had the Kd of 17.6 L kg-1 carbofuran had a bit leached. That is estimated to result from the differences of half-life of 14 days and 30 days and vapor pressure of 2.9 and 0.08mPa. These results suggested that pesticide leaching fractions are influenced by a lot of factors such as Kd values, organic matter affinity, vapor pressure, half-life of pesticide in soil, retention time, soil physical and chemical properties. Accordingly, we tried to interpret the leaching fraction values(C/C0) from lysimeter using retardation factor(RF) and attenuation factor(AF) which considered those factors, The leaching fraction values(C/C0), based on RF 10 of leaching criteria, were adapted for alachlor, carbofuran and ethoprophos in both Donghong and Jeju soil series. Even though that of carbofuran in Pyungdae soil series and that of napropamide and tebuconazole in Donghong soil series showed more than RF 10, they actually leached, meaning not being agreed with the Kd and RF estimate. The leaching fraction values(C/C0), based on AF 0.0001 of leaching criteria, those of 0.001 ∼ 0.16 in Donghong and 0.008 ∼ 0.04 in Jeju soil series were in agreement with the calculated values. In conclusion, pesticide leaching fraction from Jeju island soils with various organic matter can be estimated by a natural log-transformed AF or AFT, which are influenced by Kd values, affinity between pesticide and soil organic matter, retention time, vapor pressure and half-life of pesticide in soil, soil physical and chemical properties. This confirmed factor suggests to be easily calculated from the data like soil map(field water capacity, soil depth, soil bulk density, porosity), ground water fact sheet(recharge rate, hydraulic conductivity), and pesticide manuals(pesticide half-life in soil, adsorption coefficient, Kd = Koc * foc).