Environ. Sci. Technol. 2009, 43, 4260–4266
Origins and Transport of Aquatic Dioxins in the Japanese Watershed: Soil Contamination, Land Use, and Soil Runoff Events M A S A K A Z U K A N E M A T S U , * ,†,§ YOSHIHISA SHIMIZU,† KEISUKE SATO,† SUEJIN KIM,† TASUMA SUZUKI,† BAEKSOO PARK,† REIKO SAINO,† AND MASAFUMI NAKAMURA‡ Research Center for Environmental Quality Management, Kyoto University, 1-2 Yumihama, Otsu, Shiga 520-0811, Japan, and Hiyoshi Ecological Service Co., 908 Kitanosyo, Omihachiman, Shiga 523-0806, Japan
Received December 4, 2008. Revised manuscript received March 28, 2009. Accepted March 30, 2009.
Significant dioxins accumulations in Japanese forests and paddy fields have been observed, and surface soil runoff caused by rainfall and irrigation (i.e., soil puddling in paddy fields) results in dioxins input into the aquatic environment. An extensive investigation into the origins and transport of aquatic dioxins in the Yasu watershed, Japan was conducted considering surface soil contamination level, land use, and type of soil runoff event (i.e., irrigation runoff [IR], rainfall runoff [RR], and base flow [BF]). Combined use of the chemically activated luciferase expression (CALUX) assay together with high-resolution gas chromatography and high-resolution mass spectrometry (HRGC/HRMS) efficiently enabled this study, so that origins, transport, and dynamic movement of aquatic dioxins in the watershed were revealed. The particulate organic carbon normalized particulate-dioxins WHO-toxic equivalent (TEQ) concentration predicted by the CALUX assay (Spar) was found to be a convenient molecular marker to indicate origins of aquatic dioxins and clearly reflect surface soil contamination level, land use, and soil runoff events. Using experimental results and theoretical modeling, the annual loading amount of dioxins at the middle reach of the river was estimated to be 0.458 mg WHOTEQ in 2004. More than 96.6% of the annual loading amount was attributed to RR and derived almost evenly from forest and paddy fields at the study location. Because the annual loading amount at the middle reach is less than 0.5% of the total dioxins accumulated in the upper basin, dioxins runoff from the Japanese watershed will continue. This study shows that the combined use of the bioassay with HRGC/HRMS can provide new insights into dioxins transport and fate in the environment.
Introduction Dioxins emissions from municipal/industrial waste incinerators have increased since the 1960s, and combustion * Corresponding author phone: +1 530 754 5455; fax: +1 530 752 7872; e-mail:
[email protected]. † Kyoto University. § Current address: Department of Civil and Environmental Engineering, University of California at Davis, One Shields Avenue, Davis, California 95616. ‡ Hiyoshi Ecological Service Co. 4260
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processes in those incinerators have been the primary sources of dioxins in Japan (1). Although the amount of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofuran (PCDFs) emissions has been dramatically decreasing since 1997 (1), the amount of PCDDs and PCDFs (PCDDs/DFs) emissions into the atmospheric environment in Japan (approximately 5300 g toxic equivalent (TEQ)/yr for 1998 (2)) has been higher than those in other countries (3). Once released into the atmosphere, they are subject to atmospheric deposition on the ground surface through various pathways (4, 5). They are sorbed onto the organic component of surface soils and very slowly undergo transformation and degradation. High dioxins TEQ concentrations have been detected in Japanese forest soils, and our previous research found that the dioxins TEQ concentration in forest soil showed a good linear correlation to organic carbon content (6). In contrast, a large amount of pesticides containing dioxins as byproduct was used in Japanese paddy fields during the 1960-1990s (7). It is estimated that 120-440 and 180-270 kg TEQ of PCDDs/DFs contained in pentachlorophenol (PCP) and chloronitrophen (CNP), respectively, were released into Japanese paddy fields (7). Specific congeners derived from those pesticides have been detected in Japanese paddy fields (6, 8), sediments (6, 9, 10). Although organic carbon contents in paddy soils are low (
