The Impact of Pesticides - Academy Publish

Behavior of Pesticides and Their Transformation Productsin River Water in JapanKuniaki Kawata and Tomohiro KoseINTRODUCTIONPesticides serve an important role in increasing agricultural productivity. Severalhundred different pesticides are used worldwide for agricultural production. InJapan, more than five hundred compounds are registered as pesticides foragricultural use. Manufactured pesticides exceeded 200 varieties and 250 metrickilotons in FY2009. Paddy rice farming has been playing an important role in cropproduction throughout the world. In Japan, paddy fields covered a total area of2.496 million ha, accounting for 54.3% of all land cultivated in FY2010.Approximately 170 pesticides designated for rice farming are applied to paddyfields in Japan.Pesticides applied to paddy fields have continually caused great concern because ofpesticide runoffs into rivers: some fraction of the applied pesticides flow from thepaddy fields into the rivers through drainage channels. Numerous reports havedescribed pesticide behaviors in paddy fields and rivers in Japan. In this section, wesummarize the behaviors of applied pesticides on paddy fields and the runoff ratiosof pesticides from paddy fields to rivers. Second, we describe the daily variation ofpesticides based on hourly and bihourly variations. Third, the concentration levels ofpesticides in river waters and the typical weekly variations of pesticideconcentrations are summarized. Fourth, we describe concentration levels of somepesticides and their transformation products in river water. Finally, from thestandpoint of the human health protection, we discuss the impact of some pesticidesregulated by the Environmental Quality Standard in Japan.FATES OF APPLIED PESTICIDES IN PADDY FIELDSInsecticides and fungicides are sprayed to paddy fields by aerial and groundapplications. A diagram of pesticides applied to a paddy field is presented in Fig. 1.Parts of the aerially applied pesticides exist in the air around the applied paddy areas(Kawata 2009). Pesticides in the air drift to leeward sites. They can be a majorsource of that detected in the drainage channels and rivers immediately after aerialapplications (Yoshida et al. 2007). Most of the applied pesticides became distributedbetween the soil and water in the paddy fields.Regarding herbicides, most are applied by ground application (Amano et al. 2001,Maeda et al. 2008). The applied herbicides are dissolved or suspended in paddywater. Some pesticides in the paddy water are drained with drainage and leakage ofthe paddy water (Amano et al. 2001, Maeda et al. 2008, Morohashi et al. 2012). TheAcademyPublish.org - The Impact of Pesticides203