Sudo Miki, Kunimatsu Takao, Okubo Takuya
School of Environmental Science, The University of Shiga Prefecture, Hikone, Japan.
Water Res. 2002 Jan;36(1):315-29. doi: 10.1016/s0043-1354(01)00196-8.
The concentrations and loading rates of pesticides used in paddy fields were investigated over a period of 5 years in the Seta River, which is the only natural outlet of Lake Biwa. The lake's water catchment area is 3,174 km2, 20% of which contains paddy fields. Water samples were also collected in six rivers flowing into the lake in order to compare the contamination level and concentration profile. The pesticides analyzed were four herbicides (molinate, simetryn, oxadiazon, and thiobencarb), one fungicide (isoprothiolane), and two insecticides (diazinon and fenitrothion). Molinate, simetryn, oxadiazon and isoprothiolane were found at the higher frequencies with maximum concentrations of 1.1, 0.4, 0.1 and 0.5 microg,/l in the effluent river, one or two order of magnitude higher than that of effluent in influent rivers. These peak concentrations were observed during the application period in influent rivers and two or three weeks after that in effluent river. The frequency of occurrence of thiobencarb, diazinon, and fenitrothion was relatively low and their maximum concentrations in the effluent remained below 0.1 microg/l. The decrease of molinate, simetryn and oxadiazon concentrations in the effluent river were approximated by two straight lines plotted on semilogarithmic scale. Increased loading was induced by intense rainfall, which took place during the application period. Simetryn and isoprothiolane persisted in relatively high concentrations through the year were also influenced on its loading by the heavy rainfall in the following months. The percentages of the total amount of pesticides released through Lake Biwa to the basin in downstream were estimated to be 1.3-2.9% for molinate, 5.4-10.0% for simetryn, 0.6-1.3% for oxadiazon, 0.2-0.9% for thiobencarb, 1.8-6.6% for isoprothiolane, 0.3-2.1% for diazinon. and 0% for fenitrothion.
在琵琶湖唯一的天然出水口濑田川，对稻田使用的农药浓度和负荷率进行了为期5年的调查。该湖的集水面积为3174平方公里，其中20%为稻田。还在流入该湖的六条河流中采集了水样，以比较污染水平和浓度分布。分析的农药有四种除草剂（禾草敌、西草净、恶草酮和杀草丹）、一种杀菌剂（异稻瘟净）和两种杀虫剂（二嗪农和杀螟硫磷）。禾草敌、西草净、恶草酮和异稻瘟净的检出频率较高，在流出河中最大浓度分别为1.1、0.4、0.1和0.5微克/升，比流入河中流出水的浓度高一个或两个数量级。这些峰值浓度在流入河的施用期观察到，在流出河则在施用期后两到三周观察到。杀草丹、二嗪农和杀螟硫磷的出现频率相对较低，其在流出水中的最大浓度仍低于0.1微克/升。流出河中禾草敌、西草净和恶草酮浓度的下降在半对数尺度上用两条直线近似表示。施用期的强降雨导致负荷增加。西草净和异稻瘟净全年都保持相对较高的浓度，随后几个月的暴雨也对其负荷产生了影响。通过琵琶湖排放到下游流域的农药总量百分比估计为：禾草敌1.3 - 2.9%，西草净5.4 - 10.0%，恶草酮0.6 - 1.3%，杀草丹0.2 - 0.9%，异稻瘟净1.8 - 6.6%，二嗪农0.3 - 2.1%，杀螟硫磷为0%。
