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Insights into the degradation of chlordecone in nature

Using NMR spectroscopy to detect cell morphology alterations in vivo
Researchers at Genoscope's Genomics Metabolics lab have identified about twenty transformation products resulting from the degradation of chlordecone (a compound classed as a persistent organic pollutant) and furthermore demonstrated their presence in French West Indies soils. The team's work raises questions as to the management of these potentially novel pollutants.

Published on 31 July 2019

Chlordecone is an organochloride insecticide that was classified as a persistent organic pollutant in 2001. Although now prohibited, it was widely used in the French West Indies between 1972 and 1993, resulting in massive, persistent pollution of the islands' soils, water resources and shorelines. Today still, a large part of the Antilles population continues to be affected by the resulting contamination of animal, plant and ocean foodstuffs. Chlordecone has been recognized as an endocrine disruptor and chronic exposure to it tied to an increased risk of prostate cancer1,2 and to delayed development in children3,4.

The compound has been considered non-biodegradable and resultantly researchers have estimated durations of land contamination ranging from several decades to even centuries, depending on the nature of the soil. These scientific findings illustrate the scale of the environmental, socioeconomic and public health issues endured by the people of the French West Indies.

In an article published in Environmental Science & Technology, researchers from Genoscope's Genomics Metabolics laboratory report their work over ten years on chlordecone biodegradation. In the lab, they identified close to 20 chlordecone transformation products, obtained in the presence of diverse microorganisms.

To better characterize those products, the team went on to synthesize them chemically and apply combinations of chromatography, mass spectrometry and nuclear magnetic resonance analyses to determine the precise structure of the products. They thereafter grouped them into five families according to their structural similarities. Four of the families presented indene ring systems5 that differ greatly from the polycyclic structure of the parent compound. These products result from the opening of chlordecone's cage-like core molecular structure, thought to confer the compound's great stability.

Having elucidated the structure of the transformation products, the team turned its attention to finding them in the French West Indies (Martinique) via a first prospective in-the-field study. This latter indeed demonstrated the systematic presence of the chlordecone transformation products, not only in all soil samples taken where the insecticide had been used, but also in river and mangrove water samples and mangrove sediment samples. In all, 17 transformation products were identified, several of which showed concentrations comparable to that of chlordecone itself. Microbiological experiments done in the lab confirmed that all types of Antilles soils are able to induce chlordecone degradation in several weeks.

The team's work has shaken up the current knowledge of chlordecone by showing that it does indeed degrade in Antilles soils, progressively releasing significant quantities of transformation products. By revealing these transformation products as probable emerging pollutants, the team has profoundly modified our understanding of this type of pollution and brought into question its management. Additional studies will be needed to assess the toxicity of the products, their potential presence in foods and the population's exposure to them.

1 : Deloumeaux et al., Prostate cancer clinical presentation, incidence, mortality and survival in Guadeloupe over the period 2008−2013 from a population-based cancer registry. Cancer Causes & Control 

2 : Brureau et al., Endocrine disrupting-chemicals and biochemical recurrence of prostate cancer after prostatectomy: A cohort study in Guadeloupe (FrenchWestIndies). Int.J.Cancer 

3 : Dallaire et al.. Cognitive, visual, and motor development of 7-month-old Guadeloupean infants exposed to chlordecone. Environ. Res. 

4 : Boucher et al. Exposure to an organochlorine pesticide (chlordecone) and development of 18-month-old infants. NeuroToxicology

5: Indene is a bicyclic hydrocarbon of formula C9H8. It is composed of a benzene ring fused with a cycle of cyclopentadiene

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