The influence of soil redox conditions on atrazine degradation in wetlands

The biotransformation of atrazine as affected by soil redox conditions was investigated in soil collected from a Taxodium distichum/Nyssa aquatic (bald cypress/water tupelo) swamp-forest receiving run-off from sugarcane growing on adjacent natural levees of the Mississippi River Deltaic Plain, LA. The soil was incubated under controlled redox conditions over a range representing both reducing and oxidizing conditions (-164, +169, +392, and +584 mV). The atrazine biotransformation rate was extremely rapid in oxidized soil (+392 mV and +584 mV). The concentration of atrazine dropped from approximately 70 mu g g(-1) soil to non-detectable levels after only two weeks of incubation under both oxidized redox treatments. Biotransformation of atrazine was considerably slower in soils maintained under reducing or anaerobic redox conditions (-164 mV and +169 mV). From an initial atrazine concentration of 70 mu g g(-1) soil, 9 mu g g(-1) and 3 mu g g(-1) atrazine, respectively, remained after 99 d for soil incubated at -164 mV and +169 mV. This study shows that there is a very clear demarcation in atrazine biotransformation between soil redox levels representing aerobic and anaerobic conditions. There was no significant difference in biotransformation between the two anaerobic redox treatments and between the two aerobic redox treatments. Results shows that atrazine will be more persistent under, anaerobic conditions such as found in wetlands or subsurface environments than in more oxidizing environments such as surface agricultural soils in which it is commonly applied as a herbicide. (C) 1997 Elsevier Science B.V.