Accelerated sediment transfers may lead to delayed environmental pollution: the case of chlordecone insecticide in the French West Indies

Among contaminants leading to widespread environmental contamination and associated population and ecosystem health problems, the chlordecone insecticide has been in the spotlight in the last several decades. This organochlorine substance has been intensively used to fight against the banana weevil in the multiple banana plantations of the French West Indies between 1972 and 1993. More than 30 years after its official ban, it is still found in multiple environmental compartments of Martinique and Guadeloupe Islands, and its persistence in the environment remains strongly debated within the scientific community.

In order to shed new light on this question, an original experimental approach combining the detection of chlordecone and that of fallout radionuclides (Pb-210, Cs-137) in soil and sediment cores collected in a cultivated headwater catchment was carried out (Saint-Esprit, Martinique). Fallout radionuclides indeed provide powerful tools to date lacustrine sediment cores and reconstruct soil redistribution rates since the onset of the atmospheric nuclear tests mostly conducted in the 1950s and 1960s.

This approach showed that high and unsustainable erosion rates (i.e. 10 t ha⁻¹ yr⁻¹) took place in the study area during the study period (1980-2023). This excessive erosion was associated with a significant transfer of particle-bound chlordecone insecticide that was shown to accumulate in colluvial deposits generated at the bottom of hillslopes planted with banana trees. These transfers accelerated in time, with an increase detected in lacustrine sediment cores in 2006 in response to change in landscape management practices (e.g. through the introduction of herbicides to remove weeds under plantations). 

Overall, when considering the measured pesticides stocks in the catchment and when taking account of pesticide particle-bound transfers only, this experimental approach led to estimations of chlordecone residence times in the landscape comprised between 4000 and 11,000 years, which urges to take measures to limit soil erosion and transfers of contaminated sediment to downstream environments.