Studies on concentration, decomposition rate, half-life time and degradation products of herbicide diuron in river waters of Hiroshima prefecture, Japan

SAKUGAWA Hiroshi, TAHARA Kosaku, AOKI Kazutomo, ARAI Naotomo, NAKATANI Nobutake, TAKEDA Kazuhiko

doi:10.14934/chikyukagaku.44.1

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a heavily applied herbicide for both agricultural, other than rice paddies, and non-agricultural uses. In this study, we measured the concentration of diuron in river waters in Hiroshima prefecture, Japan, and determined photochemical and biological degradation rates, half-life and its degradation products. From April to October in 2004, water was taken from the Kurose and Ashida rivers. Diuron was extracted by solid phase extraction and then measured by high performance liquid chromatography with UV detection. The concentration range of diuron in the river water analyzed was 0.35〜3.6μg L^-1 (av. 0.69μg L^-1). The photochemical decomposition rate of diuron added into the rivers was determined by irradiation for several hours of the collected water samples using a solar simulator, or by using natural sunlight for 12-25 days. The direct photolysis constant of diuron in water was k_DP=3.38×10^-5s^-1 when the photolysis rate constant was normalized to the solar noon conditions of 34°N in spring. The indirect photolysis constant via oxidation with hydroxyl radical (OH) was determined as k_IP= 9.29×10⁹ M^-1s^-1. In the Kurose river, the half-life of diuron by direct, indirect and total photolysis was estimated as 5.7, 5.8〜43 and 2.9〜5.0h, respectively. The half-life of diuron was 9〜38d when the water samples were irradiated using natural sunlight (October-December, 2006). Biodegradation of diuron was examined by incubating unfiltered river waters containing diuron at 21°C in the dark for three months. The biodegradation half-life of was 602〜814 d. The degradation products of diuron through photo and biodegradation processes were analyzed by liquid chromatography - mass spectrometry and gas chromatography - mass spectrometry. 3-(3-chloro-4-hydroxyphenyl)-dimethylurea, 3-(4-chloro-3-hydroxylphenyl)-dimethylurea and 3,4-dichloroaniline were identified, but other 4 compounds were not. It was estimated that a significant portion of diuron discharged into river water in Hiroshima prefecture was transported into the Seto Inland Sea, without any or with only a little degradation; thus being a potential source of pollution in coastal waters.

Studies on concentration, decomposition rate, half-life time and degradation products of herbicide diuron in river waters of Hiroshima prefecture, Japan

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