Study of a vertical profile of pre-emergence herbicide contamination in Middle Garonne sediments

Abstract

The fate of pre-emergence herbicides was investigated in sediment cores at sites selected for their nested sedimentation rates. Sediment was segregated in the coarse fraction (>63 µm) and in clays and silts (<63 µm) from the surface to a 45-cm depth. The fine fraction was more contaminated than the coarse fraction, mainly because of desethylatrazine (DEA). However, pesticides were observed in sediments at depths dated to before these compounds were used. Contaminated ancient sediments showed that contaminated elements migrated into the sediment. The fine fraction DEA profile was associated with the chronology of atrazine use. Comparing the sediment age, the half-life of the pesticides studied and banning dates showed that a non-degraded pesticide stock can be established in sediment.

Keywords:

• s-triazines
• substituted ureas
• anilides
• pesticides
• sediment
• core

Acknowledgements

This study was conducted within the GISECOBAG, Programme P2 ‘Mid-Garonne River’, and supported by funds from CPER and FEDER (grants no. OPI2003-768) of the Midi-Pyrenees Region and Zone Atelier Adour Garonne (ZAAG) of PEVS/CNRS-INSUE. Special thanks are extended to Francis Dauba for his helpful technical assistance and Mancies' dam staff for their availability and kind help.