Gibbs Free Energy of Formation of Chlordecone and Potential Degradation Products: Implications for Remediation Strategies and Environmental Fate

Abstract

Chlordecone (C 10 Cl 10 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 f H m °and Δ f G m °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 E o ′ 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.

Natural transformation of chlordecone into 5b-hydrochlordecone in French West Indies soils: statistical evidence for investigating long-term persistence of organic pollutants

“…The volatility and solubility of 5b-hydroCLD have never been determined experimentally. From thermodynamic data, Dolfing et al (2012) have estimated that 5b-hydroCLD has a Henry's constant of 0.00284 Pa m or liquid chromatographic analysis using apolar columns (Carver and Griffith 1979;George et al 1986;Belghit et al 2015; this article, data not shown). This elution order is indeed experimental evidence that 5b-hydroCLD is more polar than CLD and so necessarily more soluble in a polar solvent like water.…”

“…The coupling of this FeIII/FeII cycling to the dechlorination of chlorinated compounds has been demonstrated at lab scale (Li et al 2008(Li et al , 2009) and could work for the CLD/5b-hydroCLD redox couple. CLD/5b-hydroCLD has indeed a redox potential of +414 mV (Dolfing et al 2012), which indicates that it can act as an electron acceptor for the 'iron oxide'/FeII couples, this part of the process being merely abiotic (Fig. 3).…”

“…3 Hypothetical abiotic and biotic processes that may contribute to the formation of 5b-hydroCLD through CLD dechlorination in the different soil compartments (surface, bulk soil, anoxic microniches): photoreaction (1), direct microbial dechlorination by aerobic (2) and/or anaerobic (3) microorganisms and indirect abiotic dechlorination through the FeIII/FeII cycle mediated by iron reducing bacteria (4). The CLD/5b-hydroCLD redox potential value given in the redox scale corresponds to that calculated by Dolfing et al (2012). All the other redox potentials were taken from Majzlan (2013) except for FeII/Fe° (Dolfing et al 2008).…”

“…However, according to the theoretical study performed by Dolfing et al (2012), there should be no thermodynamic restriction to the ultimate biological mineralization of CLD under a wide range of redox conditions (O 2 ,Fe 3+ , NO 3 − , SO 4 2− and CO 2 as main electron acceptors; Dolfing et al 2012). Its partial transformation by reductive dechlorination should be also possible but probably restricted to (or at least favoured in) anaerobic environments rich in labile organic matter as electron donor for the process (Dolfing et al 2012). Such conditions do not correspond to the situation in the FWI for soils used to grow bananas (andosol, ferralsol and nitisol) that are too draining for allowing anaerobiosis.…”

Effects of chlordecone on 20-hydroxyecdysone concentration and chitobiase activity in a decapod crustacean, Macrobrachium rosenbergii

“…Nowadays, CLD is still present in soils, especially in the densely cultivated areas from south of Basse-Terre (Guadeloupe) (Cabidoche et al, 2009). Although, Fernández-Bayo et al (2013) showed the existence of CLD degrading organisms in a tropical soil (andosol) microcosm under aerobic conditions, CLD undergoes no significant or quick biotic or abiotic degradation (Dolfing et al, 2012;Levillain et al, 2012). Driven by the water cycle, CLD in soils is progressively transferred to aquatic ecosystems (Coat et al, 2011) and also in the food web because of its high K oc (Soil Organic Carbon Water Partitioning Coefficient) (15849 L/Kg), K ow (Octanol-Water Partition Coefficient) (4.5-6.0) and its affinity for lipids (Cabidoche and Lesueur-Jannoyer, 2012;Clostre et al, 2013;Sterrett and Boss, 1977;UNEP, 2005;US-EPA, 2008).…”