Mecoprop, isoproturon, and atrazine in and above a sandy aquifer: Vertical distribution of mineralization potential

The vertical distribution of the potential to mineralize [ring-U-¹⁴C]herbicides was investigated in samples from a sandy aquifer. Mecoprop, isoproturon, or atrazine were added to sediments from 0.06 to 7.68 m below the surface, and mineralization at 10°C was monitored as evolved ¹⁴CO₂. The highest potential for mineralization was found in the plough layer, the upper 0.30 m. Here, approximately 43% of mecoprop, 14% of isoproturon, and 3% of atrazine were recovered as ¹⁴CO² after 85, 267, and 119 days, respectively. The estimated doubling time, T(d), for ¹⁴CO₂ evolution from the initially added herbicide was approximately 20 days for mecoprop in the plough layer increasing to more than 5 years below 4.73 m. For isoproturon incubated at 10 °C, T(d) was 700 days in the plough layer increasing to 6 years in the subsurface. At 20 °C the rate of mineralization of isoproturon doubled compared to the rate at 10 °C. Atrazine was mineralized slowly, T(d) was 5 years in the plough layer, and mineralization of atrazine below 0.70 m was not observed. None of the herbicides was mineralized anaerobically in the presence of nitrate.