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

The potential to mineralize 2,4-dichlorophenoxyacetic acid (2,4-D), mecopro p, isoproturon and terbuthylazine was studied in soil and aquifer chalk sam pled at an agricultural field near Aalborg, Denmark. Laboratory microcosms were incubated for 258 days under aerobic conditions at 10 degreesC with so il and chalk from 0.15-4.45m below the surface. The [ring-U-C-14]-labeled h erbicides were added to obtain a concentration of 6 mug kg(-1) and minerali zation was measured as evolved [C-14]carbon dioxide. The herbicides were re adily 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 [C-1 4]carbon dioxide. Large variations in both rate and extent of mineralizatio n were observed within replicates in chalk. No mineralization of terbuthyla zine in chalk was observed. As a measure of the general metabolic activity towards aromatic compounds, [ring-U-C-14]-benzoic acid was included. It was readily mineralized at all depths. (C) 2000 Society of Chemical Industry.