Mineralization of 2,4-D, mecoprop, isoproturon and terbuthylazine in a chalk aquifer.

The potential to mineralize 2,4-dichlorophenoxyacetic acid (2,4-D), mecoprop, isoproturon and terbuthylazine was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. Laboratory microcosms were incubated for 258 days under aerobic conditions at 10 degrees C with soil and chalk from 0.15-4.45 m below the surface. The [ring-U-14C]-labeled herbicides were added to obtain a concentration of 6 micrograms kg-1 and mineralization was measured as evolved [14C]carbon dioxide. The herbicides were readily mineralized in soil from the plough layer, except for terbuthylazine, which was mineralized only to a limited extent. In the chalk, lag periods of at least 40 days were observed, and a maximum of 51%, 33% and 6% of the added 2,4-D, mecoprop and isoproturon, respectively, were recovered as [14C]carbon dioxide. Large variations in both rate and extent of mineralization were observed within replicates in chalk. No mineralization of terbuthylazine in chalk was observed. As a measure of the general metabolic activity towards aromatic compounds, [ring-U-14C]-benzoic acid was included. It was readily mineralized at all depths.

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