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Óм¸¶ÎÓ¢ÎÄ£¬°ïæ¿´Ï·ÒëµÄÎÊÌâ £¨The effects of zero-valent iron (Fe0) on the degradation of HCHs £©À¨»¡ÄÚµÄΪÌâÄ¿ The time dependence of HCHs concentration is given in Fig.1. The concentration of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH in treatment without zero-valent iron (Fe0) decreased dramatically during 40 days (Fig.1), the percentage degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH is 77%, 80% and 62%, respectively, after 40 days incubation. However, the additional of zero-valent iron (Fe0) can not facilitate the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH, it shows little effect on the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH. In contrast, the concentration of ¦Â-HCH in treatment without Fe0 had no apparent change in total 40 days (Fig.1), but the additional of zero-valent iron (Fe0) can facilitate the degradation of ¦Â-HCH. The concentration of ¦Â-HCH in the treatment with the addition of 0.5% Fe0, 2% Fe0 and 5% Fe0 decreased by 23%, 34% and 44%, respectively, after 40 days incubation. It is evident that ¦Â-HCH responded intensively to zero-valent iron and the more amount of Fe0, the higher the percentage degradation of ¦Â-HCH reach. Fig. 1 The concentration of ¦Á-HCH, ¦Ã- HCH and ¦Ä-HCH decreased dramatically in the absence and presence of Fe0 within 40 days. In contrast, the percentage degradation of ¦Â-HCH had no apparent change in total 40 days in the absence of Fe0, but ¦Â-HCH responded intensively to zero-valent iron and the more amount of Fe0, the higher the percentage degradation of ¦Â-HCH reach. This may be attributed to the characteristics that ¦Á-HCH, ¦Ã- HCH and ¦Ä-HCH can biodegrade both under aerobic condition and anaerobic condition, and the biodegradation of ¦Â-HCH need anaerobic condition. HCH biodegradation was initially thought to be an anaerobic process ( MacRae et al., 1984; Sethunathan et al.,1983) and dechlorination of all four commonly found HCH isomers (¦Á, ¦Â, ¦Ã, ¦Ä-HCH) has been observed under anoxic conditions in soil microcosms (Jagnow et al., 1977), soil slurries (MacRae et al., 1984; Siddaramappa et al., 1975) and pure cultures (Jagnow et al., 1977). However, ¦Á-HCH and ¦Ã-HCH were also biodegraded aerobically in soil and soil slurries in microcosms (Bachmann et al., 1988a,b; Bhuyan et al., 1992; Francis et al., 1975; MacRae et al.,1984; Wada et al., 1989), field plots of soil (Doelman et al. 1990) and pure cultures (Johri et al. 1998). But ¦Â-HCH isomer is indisputably the most recalcitrant isomer (Phillips et al., 2005) and a strongly negative redox potential was needed for ¦Â-HCH removal (Siddaramappa et al.,1975; Van Eerkert et al.,1998). In this study, the oxidation-reduction potential of treatment without Fe0 remained about 400mv for the duration of the experiment and the system is in aerobic environments (Fig.2). The addition of Fe0 had significant effect on the oxidation-reduction potential. The oxidation-reduction potential of treatment with Fe0 decreased rapidly from a level of +400 mV to less than -200 mV, and Fe0 generated a reduced environment in soils. Furthermore, the more amount of Fe0, the lower the oxidation-reduction potential is. Fig. 2 In this study, ¦Á-HCH, ¦Ã- HCH, ¦Ä-HCH are more easily biodegraded than ¦Â-HCH both in the absence of Fe0 and in the presence of Fe0. The relative persistence of each isomer is generally attributed to the orientation of the chlorine atoms on the molecule. In the ¦Á-, ¦Â-, ¦Ã-, ¦Ä-HCH, the chlorine atoms have ¡®aaaaee¡¯, ¡®eeeeee¡¯, ¡®aaaeee¡¯ and ¡®aeeeee¡¯ orientations, respectively (Phillips et al., 2005). The presence of axial chlorine atoms was thought to provide available sites for enzymatic degradation (Phillips et al., 2005). ¦Â-HCH, the most persistent isomer (Bachmann et al. 1988b; Beurskens et al. 1991; Johri et al.1998; Sahu et al. 1990, 1993), has all equatorially oriented chlorine atoms (¡®eeeeee¡¯), resulting in a more structurally stable compound. |
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£¨The effects of zero-valent iron (Fe0) on HCHs degradation£© The time dependence of HCHs concentration is shown in Fig.1. The concentration of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH decreased dramatically in the treatments without zero-valent iron (Fe0) (Fig.1). After 40 days incubation, the degradation percentage of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH is 77%, 80% and 62%, respectively. Surprisingly, zero-valent iron (Fe0) shows little effect on the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH...... ¿´ÁËÒ»²¿·Ö£¬Ö÷ÒªÊÇÈßÓàµÄ벡¡£ |
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In contrast, the concentration of ¦Â-HCH in treatment without Fe0 had no apparent change in total 40 days (Fig.1), had ¸Ä³É showed£¬¸üµØµÀЩ |

3Â¥2009-07-25 09:25:14
xinyunsina
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the percentage degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH is 77%, 80% and 62%, respectively, after 40 days incubation. However, ithe additional of zero-valent iron (Fe0) can not facilitate the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH it shows little effect on the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH. s Ó¦¸Ã¸ÄΪwere£¬ the additional of zero-valent iron (Fe0) can not facilitate the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCH ºÍ it shows little effect on the degradation of ¦Á-HCH, ¦Ã-HCH and ¦Ä-HCHÖØ¸´ |
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