hydroxyl ion at pH >∼7.4, consistent with eq 4. The much
smaller slope at pH <7.4 suggests that the acid-catalyzed
and neutral hydrolysis is likely a zeroth-order reaction with
respect to hydroxyl ion.
The base-catalyzed second-order hydrolysis rate constant
kb can be calculated using the following:
model equations. This material is available free of charge via
the Internet at http:/ / pubs.acs.org.
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(10)
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Rates of γ-HCH Transform ation in the FeS-Containing
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CHCH ) CHCH,0e-k ′t
(11)
3
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tions (Table 1).
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This study provides insight information on the fate of
HCH isomers in the aquatic ecosystems. It is expected that
transformation of other HCH isomers such as R- and â-HCH
may be enhanced similarly in FeS-containing systems. Such
enhanced transformation rates should be incorporated to
the models for predicting fate and transport of HCH in aquatic
systems. Modeling exercises using the hydrolysis rate pa-
rameters measured for homogeneous systems may signifi-
cantly overestimate the persistency of HCH in large-scale
environmental systems. As less chlorinated aromatic products
such as DCBs are relatively more volatile and can undergo
aerobic degradation and photolysis at much faster rates than
their parental HCHs (28), monitoring the environmental fate
of these finial products of HCH transformation along with
the HCH isomers should be considered.
Acknowledgments
The authors thank Dr. Elizabeth Butler of the University of
Oklahoma and an anonymous reviewer for their valuable
suggestions and comments on this study. We greatly ap-
preciate the assistance of Professors Jinzhong Liu, Guoying
Sheng, and Huizhi Zhang; Dr. Zhiqiang Yu; Ms. Chiling Yu;
and Mr. Tongshou Xiang at Guangzhou Institute of Geochem-
istry, Chinese Academy of Science, during the experimental
phase of this study. Financial support was provided in part
by Guangdong Foundations of Natural Science (Team Project
20003046) to P.P. and in part by The National Natural Science
Foundation of China (40128002) through the International
Young Investigator Program to W.H.
Supporting Information Available
Three figures (representative GC chromatograms and GC-
MS spectra indicating the presence of intermediate and final
products) and details of mathematical derivation of kinetics
Received for review June 27, 2002. Revised manuscript re-
ceived December 20, 2002. Accepted February 9, 2003.
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