Gibbs Free Energy of Formation
of Chlordecone and
Potential Degradation Products: Implications for Remediation Strategies
and Environmental Fate
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Abstract
Chlordecone (C<sub>10</sub>Cl<sub>10</sub>O; CAS number
143-50-0)
has been used extensively as an organochlorine insecticide but is
nowadays banned under The Stockholm Convention on Persistent Organic
Pollutants (POPs). A search for chlordecone-respiring organisms and
choosing between reductive versus oxidative remediation tools and
strategies to clean up chlordecone-polluted environments would benefit
from the availability of Gibbs free energy data of chlordecone and
its potential dechlorination products. Presently such data are not
available. Polycyclic “cage” molecules of which chlordecone
is an example contain considerable strain energy. It is not a priori
clear how this affects the thermodynamic properties of the chlorinated
members of this unique class of compounds and to what extent redox
potentials for the halogenated congeners are different from those
of other aliphatic and aromatic organohalogens. We performed ab initio
quantum chemical calculations to estimate Δ<sub>f</sub><i>H</i><sub>m</sub>° and Δ<sub>f</sub><i>G</i><sub>m</sub>° values of chlordecone and selected dechlorination
products and used these data to calculate their Gibbs free energy
and redox potential. With redox potentials in the range of 336–413
mV chlordecone has an <i>E</i><sub>o</sub>′ value
similar to that of other organochlorines. The results indicate that
there are no thermodynamic reasons why chlordecone-respiring or -fermenting
organisms should not exist