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

The vertical distribution of the potential to mineralize [ring-U-C-14]herbi cides was investigated in samples from a sandy aquifer. Mecoprop, isoprotur on, or atrazine were added to sediments from 0.06 to 7.68 m below the surfa ce, and mineralization at 10 degrees C was monitored as evolved (CO2)-C-14. The highest potential for mineralization was found in the plough layer, th e upper 0.30 m. Here, approximately 43% of mecoprop, 14% of isoproturon, an d 3% of atrazine were recovered as (CO2)-C-14 after 85, 267, and 119 days, respectively. The estimated doubling time, T-d, for (CO2)-C-14 evolution fr om 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 isoprotu ron incubated at 10 degrees C, Td was 700 days in the plough layer increasi ng to 6 years in the subsurface. At 20 degrees C the rate of mineralization of isoproturon doubled compared to the rare at 10 degrees C. Atrazine was mineralized slowly, rd was 5 years in the plough layer, and mineralization of atrazine below 0.70 m was not observed. None of the herbicides was miner alized anaerobically in the presence of nitrate.