Formation and Movement of¹⁴C-Atrazine Degradation Products in a Sandy Loam Soil Under Field Conditions

Formation and distribution of 14 C-atrazine degradation products in the top 120 cm of soil were determined over 16 mo under field conditions in an Estherville sandy loam. After 16 mo, 78% of applied 14 C was still present in the soil. By 2 mo after treatment (MAT), 14 C had moved to the 30- to 40-cm depth; however, movement to depths greater than 40 cm was not observed. Greater than 98% of the 14 C remaining in the soil profile after 16 mo was in the top 20 cm. Twenty-seven percent of the 14 C applied was atrazine 16 MAT. Atrazine was the predominant 14 C-compound in soil below 10 cm. Hydroxyatrazine (HA) was the major degradation product in the top 10 cm of soil. The proportion of 14 C as HA in the top 10 cm increased from 15% 2 MAT to 37% 16 MAT. Deethylatrazine (DEA) was the predominant degradation product at the 10- to 30-cm depth and accounted for up to 23% of the 14 C present in the 10- to 20-cm depth. Deisopropylatrazine (DIA) accounted for less than 6% of the radioactivity recovered at any soil depth. The proportion of DEA and DIA increased while the proportion of HA decreased as soil depth increased, indicating that DEA and DIA are more mobile in soil than HA. Detection of HA at depths greater than 10 cm appears to be due to in situ degradation of atrazine previously moved to that soil depth. The large amount of 14 C remaining in the soil 16 MAT suggests that a large pool of atrazine and its degradation products are present in the soil for an extended period following application and have the potential to contaminate ground water.