摘要：For the purpose of preserving the water quality, we investigated the annual variation in the concentration levels and frequency of detection of 36 kinds of regulated pesticides in water sources in Hyogo Prefecture before and after the enforcement of the new Water Quality Standard for drinking water revised by the order of Minister based on Water Works Law on December 1 in 1993. The samples measured consisted of 665 samples of water sources. In most of the samples analyzed, the concentration levels of pesticides were under one tenth of regulated values of supplied water. On the other hand, 3 kinds of pesticides, such as simazine, isoprothiolane and flutoluanil had especially high frequency of detection (over 15%) before the new Water Quality Standard enforced. However, after the new Water Quality Standard enforced, both the concentration levels and frequency of detection of three pesticides analyzed were decreasing annually. Distribution patterns of pesticides supplied from different water sources were analyzed and grouped as follows : Group 1 : In river and lake (dam, reservoir) water, the frequency of detection of pesticides were higher than those in other water sources. The high frequency of detection of pesticides in lake (dam, reservoir) water are especially due to the closed systems. Group 2 : In unconfined water such as the water from shallow well and river-bed water the several pesticides were observed at times. Group 3 : In confined water such as the water from deep well and self-flowing water none of the pesticides were detected in every time.
