Water isotopes and chemical tools for understanding pesticide transfer in a watershed of the volcanic island of Martinique (French West Indies)

ABSTRACT

Monitoring of water quality over several years has revealed a persistent pesticide contamination of surface and groundwater in several Caribbean Islands, with pesticide concentrations locally over the drinking-water limit set in Europe, i.e. 0.1 µg L^–1 per substance. For Martinique, mainly one pesticide, chlordecone (CLD), remains of major concern despite its withdrawal from the market in 1993. Since the first sampling campaign in 1999–2000, time and space variations of CLD concentrations in surface water and groundwater are still not well understood and difficult to correlate with climate, geological or hydrogeological contexts. We carried out a study in the Chalvet catchment (northeast Martinique) in order to understand more precisely how water movements may explain pesticide transfer. Various tools such as δ²H - δ¹⁸O and chemical parameters were used. Deuterium excess d was proven relevant for determining how CLD is transported in groundwater; it highlighted the role of the groundwater/surface water interaction in spatial and temporal variability of surface water quality. The resulting conceptual hydrogeological model also helps understanding why CLD still has high concentrations in surface water. The approach proposed here can be used in other Caribbean islands that are poorly equipped for explaining pesticide occurrences in surface waters.

KEYWORDS:

• Chlordecone
• d-excess
• groundwater
• hydrogen-2
• isotope hydrology
• Martinique
• oxygen-18
• pollutant transfer

Acknowledgments

Dr H.M. Kluijver edited the final English version of the manuscript, S. Pinson prepared the location map.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the OLE , DEAL in Martinique and BRGM funding through BRGM .