Delayed environmental pollution caused by transient landscape storage - An example from the Lesser Antilles

Area of Science:

• Environmental Science
• Soil Science
• Hydrology
• Toxicology

Background:

• Intensive banana cultivation in the French West Indies extensively used chlordecone (an organochlorine insecticide) from 1972 to 1993.
• Chlordecone poses significant environmental and health risks, prompting research into its transfer, yet particle-bound fractions remain understudied.
• Previous research primarily focused on the dissolved fraction of chlordecone, neglecting the particle-bound component's environmental fate.

Purpose of the Study:

• To reconstruct multi-decadal erosion rates and particle-bound chlordecone transfers in a tropical agricultural catchment (1980-2023).
• To investigate the formation and erosion of chlordecone-contaminated colluvial deposits in banana plantation soils.
• To assess the long-term persistence and implications of legacy chlordecone contamination in agricultural landscapes.

Main Methods:

• Analysis of sediment cores from an agricultural reservoir to determine sediment accumulation and erosion rates.
• Sampling and analysis of soil cores along a banana plantation hillslope to identify contamination hotspots and depositional zones.
• Quantification of particle-bound chlordecone transfers from soil erosion to downstream water bodies.

Main Results:

• High erosion rates (averaging 10 t ha⁻¹ yr⁻¹) were recorded, significantly exceeding tolerable soil loss rates in tropical contexts (2.2 t ha⁻¹ yr⁻¹).
• Colluvial deposits with substantial chlordecone contamination were identified on hillslope toes, leading to massive particle-bound chlordecone remobilization.
• A significant increase in chlordecone transfers to the reservoir was observed since 2006, coinciding with agricultural practice changes.

Conclusions:

• Legacy chlordecone contamination persists in toeslope deposition zones, with estimated residence times of 4,000 to 11,000 years.
• Effective land management strategies are crucial to mitigate soil erosion and protect water bodies from ongoing chlordecone transfer.
• Minimizing soil-erosive agricultural practices, such as herbicide application and intensive ploughing, is recommended to reduce contamination risks.