Sorption and Desorption of Atrazine, Deethylatrazine, and Hydroxyatrazine by Soil and Aquifer Solids

Abstract

Adsorption kinetics and adsorption/desorption isotherms of atrazine (AT), and its degradation products, deethylatrazine (DEA) and hydroxyatrazine (HyA) on solids from two depths of a gleyic planosol and the underlying sandy aquifer were studied using laboratory batch systems. Adsorption of the three molecules decreased with the sampling depth of the solid. Atrazine and DEA were not adsorbed on the aquifer solids, whereas HyA was. For all three solids, the adsorption increased in the order DEA < AT << HyA. Adsorption equilibrium was reached after 72 h for the upper soil sample (0‐0.33 m) and after 24 h for the deeper soil sample (0.9–1.05 m) for all three molecules. For HyA, equilibrium was reached after 24 h for the aquifer solid (6–7 m). High pressure liquid chromatography (HPLC) analyses showed no significant degradation of the three molecules after 72 h. The adsorption isotherms of the three molecules were described by Freundlich equations. The Kfads values ranged from 3.1 to 0.4 L kg−1 for AT, 1.5 to 0.3 L kg−1 for DEA and 7.9 to 0.9 L kg−1 for HyA. The Koc values suggested that the affinity for the organic matter bound to the solid increased in the order DEA < AT << HyA. The desorption isotherms were also described by Freundlich equations. The Kfdes value was 7.5 L kg−1 for AT in the upper soil sample and ranged from 0.1 to 31.1 L kg−1 for DEA and from 0.7 to 96.8 L kg−1 for HyA, depending on the sample. In the upper soil sample, desorption was hysteretic and DEA and HyA formed nonextractable residues, HyA more so than DEA. For the deeper soil sample for all three compounds and the aquifer solids for HyA, adsorption was completely reversible and did not lead to the formation of nonextractable residues.

Evaluation of continuous distribution models for rate‐limited solute adsorption to geologic media

“…Metal oxides play a key role in adsorbing HA [Moreau and Mouvet, 1997]. We identified the trace metal species on the Muddy Creek sand and on the clean quartz sand by chemical extraction techniques.…”

Influence de la distance sur le transfert par ruissellement de quelques substances phytosanitaires

“…En effet, tous les facteurs qui favorisent la pénétration des composés dans le sol devraient a priori accentuer l'effet de la distance. L'étape préalable aux divers mécanismes qui conduisent à cette migration est le partage des matières actives déposées en surface, dont rend compte le Koc, entre une fraction adsorbée sur les constituants du sol et une autre dissoute dans l'eau des couches supérieures (MOREAU et MOUVET, 1997 ;BOESTEN ef al., 1991), donc très mobile (SEUX ef al., 1984). Dans un sol humide, le gradient de concentration créé par ce phénomène entre l'eau des couches superficielles et celle des horizons plus profonds, provoque alors par diffusion la migration verticale des composés.…”

Comportamento do glifosato no solo e deslocamento miscível de atrazina

“…A extensão da mobilidade da atrazina está relacionada ao conteúdo de matéria orgânica do solo (Moreau & Mouvet, 1997;Mersie & Seybold, 1997), o qual, por sua vez, também está envolvido na metabolização deste herbicida. A metabolização da atrazina em hidroxiatrazina (HA), seu principal metabólito (Lerch et al, 1999), ocorre principalmente via hidrólise química, e é catalisada pelos processos de sorção (devido à matéria orgânica) e por baixos valores de pH (Lerch et al, 1998 Enfield (1985) mostrou que, ao contrário do que se pensava, o movimento de pesticidas no solo pode ocorrer também para moléculas hidrofóbicas.…”

“…Os valores do parâmetro N, para sorção, foram de 0,84 e 0,85 para PD e PC, respectivamente, mostrando isotermas de sorção não lineares para a atrazina, nas concentrações empregadas. A magnitude destes valores está de acordo com a literatura (Clay & Koskinen, 1990;Mersie & Seybold, 1996;Moreau & Mouvet, 1997;Mersie et al, 1999) e sugere um grau de sorção intermediário para a atrazina, quando comparada com moléculas altamente sorvidas (por exemplo, o glifosato e os organoclorados -Prata et al, 2000b;Roberts & Hudson, 1999, respectivamente) ou de sorção reduzida (por exemplo, o picloram e o aldicarb - Roberts et al, 1998;Roberts & Hudson, 1999 Freundlich para dessorção. 6/ Grau de linearidade da isoterma de sorção.…”

“…No caso específico desta molécula, a t 1/2 de mineralização é um parâmetro de suma importância, pois um dos principais metabólitos da atrazina, a desetilatrazina, também é fitotóxico e ainda apresenta maior toxicidade para animais e humanos do que a própria molécula original (Moreau & Mouvet, 1997).…”