Contamination of Irrigation Well Water by Residual Herbicides

Abstract

The main residual herbicides applied to citrus in Spain are atrazine, bromacil, diuron, simazine, terbuthylazine, terbumetone, terbutryn and terbacil. Some of the orchards are on continuous non-tillage system, with one or sometimes two treatments a year of the above mentioned products. Water samples from more than fifty irrigation wells located in or near citrus orchards were analysed during the last five years. Many of the water samples do not contain herbicide. There is a close relationship between rainfall episodes and herbicide detection. Concentrations are in the low range of µg/l. Bromacil was the product most commonly found. Some herbicide degradation products also appeared: DCPMU was found more frequently than DCPU; also des-alquil-s-triazines were observed. In two very shallow wells, 1 m depth, located on a sandy soil area, hydroxy-triazines were also detected.