Fate of atrazine and alachlor in redox‐treated ferruginous smectite

Abstract

The oxidation state of structural iron (Fe) in clay minerals exerts a large influence on clay surface chemistry and may affect the adsorption and degradation of pesticides in the environment. This effect, however, has been little investigated. In the present study, herbicides atrazine and alachlor were reacted with ferruginous smectite (sample SWa-1) in its oxidized, reduced (either chemically or bacterially), and reduced-reoxidized states. In some experiments the herbicide was labeled with 14C. Gas chromatography/mass spectrometry (GC-MS) was also used to detect alachlor degradation products. Compared to oxidized clays, reduction by both chemical and microbial treatments decreased the concentration of both herbicides in the surrounding solution. Reoxidized clay exhibited behavior similar to the oxidized clay. Hydrolysis-dechlorination of atrazine occurred in the presence of chemically reduced SWa-1, and GC-MS analysis of alachlor revealed at least 14 degradation products after treatment with reduced clay and only two with the oxidized clay. Interaction of atrazine and alachlor with the clay may be through a H bond with the waters of hydration surrounding interlayer cations, the extent of which should increase with increasing acidity; but under reduced conditions, the validity of this model is unclear. Reduction of structural Fe may affect pH-dependent phenomena in two ways: The increased surface charge density increases the number of hydrated interlayer cations, thereby enhancing surface acidity, and increased electron density at basal surface oxygens increases their Brønsted basicity. Atrazine could, therefore, adsorb and/or degrade through either acid or alkaline hydrolysis pathways. Increased reduction potential of the reduced clay surfaces may also promote degradation.

Triple-Element Compound-Specific Stable Isotope Analysis (3D-CSIA): Added Value of Cl Isotope Ratios to Assess Herbicide Degradation

“…Carbon, Chlorine, and Nitrogen Isotope Fractionation in ATR Abiotic Hydrolysis. Based on carbon and nitrogen isotope data alone, it has not been possible so far to clearly distinguish among oxidative N-dealkylation, 22,63 which is the main degradation route for ATR, alkaline hydrolysis, which is a relevant mechanism on clay surfaces, 54 and oxidation by indirect photolysis. 56 Also, Λ N/C values do not allow a distinction between acidic hydrolysis and biotic hydrolytic dichlorination 10,11,[21][22][23][24][25]28 (Table S14).…”

“…22 Abiotic ATR hydrolysis may also occur at high or low pH, and by abiotic mineral-catalyzed reactions. 54 Desethylatrazine and desisopropylatrazine are among the main ATR metabolites found in groundwater, formed mainly through a biotic oxidative N-dealkylation pathway. 51−53 Whereas C and N isotope fractionation during these ATR degradation processes has been previously reported, 10,11,[21][22][23][24][25][26]55,56 our recent 3D-CSIA study was the first to include Cl isotope data for ATR degradation and to allow distinguishing ATR biodegradation by oxidative dealkylation and hydrolytic dechlorination.…”

A Deep Look Into Erionite Fibres: an Electron Microscopy Investigation of their Self-Assembly

“…Therefore, a detailed analysis of the dissolution rate of both mineral species under an extended pH range is required. Finally, it should be reminded that iron-bearing smectite shows a very relevant surface chemical activity, which depends on the oxidation state of structural iron, as indicated by the several investigations aimed at studying the smectite-mediated degradation of agricultural chemicals 44 45 .…”

Effect of Soil Aeration and Phosphate Addition on the Microbial Bioavailability of Carbon-14-Glyphosate

“…Moreover, a growing body of evidence suggests that anoxic soil conditions could alter the mineralogical and surface properties of soil (Stucki et al, 2002). These alterations could affect the bioavailability and mobility of herbicides under such soil conditions (Xu et al, 2001). Such fluctuations in bioavailability warrant a more thorough investigation into the chemical and biological fate of glyphosate under both oxic and anoxic soil conditions.…”