Skip to main content
ARS Home » Research » Publications at this Location » Publication #106070
Title: FATE OF ATRAZINE AND ALACHLOR IN REDOX-TREATED FERRUGINOUS SMECTITE

Author
item XU, J - UNIV OF ILLINOIS
item STUCKI, JAMES - UNIV OF ILLINOIS
item WU, J - UNIV OF ILLINOIS
item KOSTKA, K - FLORIDA STATE UNIVERSITY
item SIMS, GERALD

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fate of pesticides in the environment is of great importance to human health and natural ecosystems. Numerous chemical and biological processes control the fate of pesticides in the environment. Recent advances in our understanding of the properties of soil minerals, such as clays, suggest that changes in minerals observed in the absence of oxygen may influence their interactions with pesticides. Such an effect, however, has not been rigorously tested. In the present study, herbicides atrazine and alachlor were reacted with clay minerals that had been chemically or biologically treated (reduced) to simulate chemical changes in the clays that occur in anaerobic (oxygen-free) environments commonly found in flooded soils and sediments. Particular attention was focused on chemical changes in iron present in the clay. The results showed that when clays were reduced, they became significantly more reactive with the pesticides, resulting in rapid degradation. As many as 14 different degradation products were observed in the case of alachlor. Furthermore, reduction enhanced the ability of clays to adsorb pesticides from the water phase. The results indicate that the fate of pesticides in flooded soils or sediments may be quite different from the fate in a well-drained environment. These findings will be useful in predicting the fate of pesticides in surface water and associated sediments, and may be helpful in the development of remedial practices to treat contaminated soil.

Technical Abstract: The fate of agricultural chemicals in the environment is of great important to human health and natural ecosystems. Reactions at mineral surfaces play a fundamental role in these processes as they affect the fate of pesticides in soils and sediments. Recent studies revealed that the oxidation state of structural Fe in clay minerals exerts a large influence on clay surface chemistry. This suggests that Fe oxidation state may also affect the adsorption and degradation of pesticides in the environment. This effect, however, has yet to be investigated. In the present study, herbicides atrazine and alachlor were reacted in batch mode with ferruginous smectitie S Wa-1 in its oxidized, reduced (either chemically or bacterially), and reduced-reoxidized states to determine the effect of structural Fe oxidation state on the herbicide. Compared to oxidized clays, reduction by both chemical and microbial treatments decreased the concentration of both herbicides in the surrounding solution. Reoxidized clay exhibited similar behavior toward the herbicide as did the oxidized clay. Further, 14C radiotracer studies showed that hydolysis-dechlorination of atrazine occurred in the presence of chemically reduced S Wa-1, and GC-MS analysis of alachlor revealed at least 14 degradation products after treatment with reduced clay and only two with oxidized clay. Evidently, both adsorption and degradation processes are involved. The same trends were observed in studies with clays reduced by microorganisms, although to a lesser extent than with chemically reduced clays. Desorption studies with microbially treated clays recovered a large fraction of the herbicide and products adsorbed to the clay indicating that adsorption is reversible.