Sorption and degradation of the herbicide 2-methyl-4,6-dinitrophenol under aerobic conditions in a sandy aquifer in Vejen, Denmark

A pulse (7 days) and a continuous (216 days), natural gradient field injection experiment with herbicides, including 2-methyl-4,6-dinitrophenol (4,6-dinitro-o-cresol, abbreviated DNOC) and a bromide tracer were conducted in a shallow, aerobic aquifer near Vejen, Denmark. The pulse and continuous plume wore monitored in a dense, three-dimensional monitoring network installed in the aquifer downgradient of the injection. The sorption and degradation of DNOC were evaluated based on moment analysis of breakthrough curves, cross sections, and snapshots of the DNOC plume and supported by results from laboratory experiments. Significant and spatially variable sorption of DNOC (Kd range, 0.10-0.98 L/kg) was observed due to a specific binding of DNOC to clay minerals. The spatial variation was mainly a result of variation in pH,with stronger sorption at lower pH, whereas other factors such as cation composition on the solid matrix appeared to be negligible. Significant degradation of DNOC in the aquifer was revealed by moment analysis of data from the continuous field injection experiment. Degradation of DNOC in the field was slow and/or subject to long lag phases, and the data suggested spatially varying degradation potentials. This was supported by the laboratory experiments. The potential for natural attenuation of DNOC in aerobic aquifers appears promising.