**3.2 Photodecomposition behaviors of pesticides**

Figure 6-10 show the photodecomposition ratios of the pesticides. These pesticides were decomposed faster than DNP and the removal efficiencies after 3 min UV irradiation were 94% (Cafenstrole), 92% (Chlorthalonil), 75% (Thiobencarb), 67% (Pencycuron), 58% (Trifluralin) and 8% (DNP). After 30 min UV irradiation, the removal efficiencies of Cafenstrole and Chlorthalonil, and Thiobencarb, Pencycuron and Trifluralin, were 98 and 94%, respectively. The UV illumination intensity in the experiments was so strong that the same removal efficiencies as with the photocatalyst were obtained without the

Photodecomposition Behaviors of Pesticides in the Source

Fig. 8. Photodecomposition of Cafenstrole

Fig. 9. Photodecomposition of Thiobencarb

for Water Supply Using an Alumina Carrier-Titanium Dioxide Photocatalyst 59

Fig. 6. Photodecomposition of Chlorthalonil

Fig. 7. Photodecomposition of Pencycuron

Fig. 6. Photodecomposition of Chlorthalonil

Fig. 7. Photodecomposition of Pencycuron

Fig. 8. Photodecomposition of Cafenstrole

Fig. 9. Photodecomposition of Thiobencarb

Photodecomposition Behaviors of Pesticides in the Source

**4. References** 

J-151-J-155

for Water Supply Using an Alumina Carrier-Titanium Dioxide Photocatalyst 61

Every pesticide has a biologically or chemically changeable structure in molecule. For example, a N-CO-N bond (Pencycuron and Cafenstrole) and a N-CO-S bond (Thiobencarb) are easily hydrolyzed. Cyano group (Chlorthalonil) is easily oxidized. Carbon-Cl bond, benzene ring and alkyl group are biologically hydroxylized (Haque & Freed, 1975; Hutson & Roberts, 1981; Matsumura & Murti, 1982; Uesugi et al., 1997; Yamamoto & Fukami, 1979). On the other hand, the scissions of a C-Cl bond, a C-F bond, a C-NO2 bond, a C-NR2 bond and a N-N bond, especially a C-Cl bond and a N-N bond, are easily occurred photochemically (Ishikawa et al., 1989, 1992; Ishikawa & Suetomi, 1993; Ishikawa, 1996; Tanizaki et al., 2005). Moreover, the photochemical scission of a C-Cl bond is faster than the photohydrolyses of organic phosphate esters (Ishikawa et al., 1992). The differences of the photodecomposition rates in these parts would have caused the differences of the photodecomposition rate or the removal efficiency after 30 min UV irradiation of each pesticide. As the photodecomposition products could not be detected by the GC/MS analysis, it was considered that these pesticides converted into the high polar compounds.

Ando, M. (2004). Standards for Drinking Water Quality. *J. Food Hyg. Soc. Japan,* Vol.45, No.2,

Coleman, W. E., Melton, R. G., Kopfler, F. C., Barone, K. A., Aurand, T. A. & Jellison, M. G.

Haque, R. & Freed, V.H. (1975). Environmental Dynamics of Pesticides. Plenum Press, New

Hutson, D.H. & Roberts, T.R. (1981). Progress in Pesticide Biochemistry Volume 1. A Wiley-

Ishikawa, S. & Suetomi, R. (1993). Utilization of Photochemical Reaction in Environmental

Ishikawa, S. (1996). Utilization of Photochemical Reaction in Environmental Chemistry.

Ishikawa, S., Baba, K., Hanada, Y., Uchimura, Y. & Kido, K. (1989). Photodecomposition of *o*-

Ishikawa, S., Eguchi, Y. & Ito, S. (2008). Decomposition Behavior of DMSO and Methanol.

Ishikawa, S., Naetoko, E., Kawamura, S., Yamaguchi, R., Higuchi, M., Kojima, T., Yamato, Y.

Ishikawa, S., Uchimura, Y., Baba, K., Eguchi, Y. & Kido, K. (1992). Photochemical Behavior

Ishikawa, S., Ueda, N., Okumura, U., Iida, Y., Higuchi, M., Naetoko, E., Tokunaga, Y. &

Chloroaniline in Aqueous Solution with Low Pressure Mercury Lamp. *Bull.* 

Report on Development of Photo-supersonic Wave Complex Technique with TNT

& Takahashi, M. (2004). Investigation of Pesticide Residues in Foods Distributed in

of Organic Phosphate Esters in Aqueous Solutions Irradiated with a Mercury

Baba, K. (2006). Removal Efficiency for Pesticides on Coagulation and Sedimentation Using Coagulant Recovered from Water Supply Sludge. *J. Japan Soc.* 

(GC/MS/COM). *Environ. Sci. Technol.,* Vol.14, 576-588

Chemistry. *J. Environ. Chem.,* Vol.3, No.2, 295-304

(I), FS Study. The University of Kitakyushu, Japan

Lamp. *Bull. Environ. Contam. Toxicol.,* Vol.49, 368-374

Kitakyushu City. *J. Food Hyg. Soc. Japan,* Vol.45, No.2, 87-94

*KITAKYUSHU ENVIRONMENTOPIA,* Vol.11, No.1, 2-5

York and London, USA and UK

Interscience Publication, Chichester

*Environ. Contam. Toxicol.,* Vol.42, 65-70

*Water Environ.,* Vol.29, No.10, 653-658

(1980). Identification of Organic Compounds in a Mutagenic of a Surface Drinking Water by a Computerized Gas Chromatography Mass Spectrometry System

Fig. 10. Photodecomposition of Trifluralin

Figure 11 shows the relationship between ln(C/C0) and t. As these pesticides were decomposed immediately, the linear relationship between ln(C/C0) and t could not be obtained.

Every pesticide has a biologically or chemically changeable structure in molecule. For example, a N-CO-N bond (Pencycuron and Cafenstrole) and a N-CO-S bond (Thiobencarb) are easily hydrolyzed. Cyano group (Chlorthalonil) is easily oxidized. Carbon-Cl bond, benzene ring and alkyl group are biologically hydroxylized (Haque & Freed, 1975; Hutson & Roberts, 1981; Matsumura & Murti, 1982; Uesugi et al., 1997; Yamamoto & Fukami, 1979). On the other hand, the scissions of a C-Cl bond, a C-F bond, a C-NO2 bond, a C-NR2 bond and a N-N bond, especially a C-Cl bond and a N-N bond, are easily occurred photochemically (Ishikawa et al., 1989, 1992; Ishikawa & Suetomi, 1993; Ishikawa, 1996; Tanizaki et al., 2005). Moreover, the photochemical scission of a C-Cl bond is faster than the photohydrolyses of organic phosphate esters (Ishikawa et al., 1992). The differences of the photodecomposition rates in these parts would have caused the differences of the photodecomposition rate or the removal efficiency after 30 min UV irradiation of each pesticide. As the photodecomposition products could not be detected by the GC/MS analysis, it was considered that these pesticides converted into the high polar compounds.
