title: Influence of humic acid on adsorption and desorption of atrazine, hydroxyatrazine, deethylatrazine, and deisopropylatrazine onto a clay-rich soil sample.
abstract: Adsorption and desorption properties of atrazine and some of its metabolites, hydroxyatrazine (AT-OH), deethylatrazine (DEA), and deisopropylatrazine (DIA), were studied with a clay-rich soil sample (clay content of 53%). A part of this soil was treated with humic acid (Soil-HA) to assess the influence of this important component of natural organic matter on adsorption and desorption processes. This study was performed using the batch approach with 1.0 g of soil, or Soil-HA, in 5.0 mL of 0.010 mol L(-)(1) CaCl(2) solution containing the herbicide and the metabolites in a concentration range between 0.010 and 5.0 mg L(-)(1). After 24 h of contact time, the suspensions were centrifuged and the four compounds were quantified in the supernatant phases by high-performance liquid chromatography. The adsorption and desorption data of both Soil and Soil-HA were properly fitted by the linearized Freundlich equation. For the untreated soil, the adsorption affinity order evaluated as a function of the K(f) values was AT-OH > AT > DIA > DEA, while desorption followed the order DEA > DIA approximately AT > AT-OH. The presence of humic acid increased significantly the adsorption of all compounds, following the same affinity order observed for the untreated soil. Increase in adsorption was especially high for AT-OH and AT. On the other hand, the dealkylated metabolites, DEA and DIA, were more easily desorbed from the Soil-HA sample, suggesting that natural organic matter facilitates the leaching of these compounds. Desorption order in the presence of humic acid was DEA > DIA > AT > AT-OH.
authors.affiliation: Instituto de Química, Universidade de São Paulo, CP 26077, 05513-970 São Paulo, SP, Brazil.
authors.forename: Gilberto
authors.initials: G
authors.lastname: Abate
authors.forename: José C
authors.initials: JC
authors.lastname: Penteado
authors.forename: Jonas D
authors.initials: JD
authors.lastname: Cuzzi
authors.forename: Godofredo C
authors.initials: GC
authors.lastname: Vitti
authors.forename: Jaim
authors.initials: J
authors.lastname: Lichtig
authors.forename: Jorge C
authors.initials: JC
authors.lastname: Masini
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000032:analysis / Q000737:chemistry*; D001280:Atrazine / Q000031:analogs & derivatives* / Q000737:chemistry*; D000077215:Clay; D006812:Humic Substances / Q000032:analysis; D006900:Hydroxylation; D012987:Soil / Q000032:analysis*; D014227:Triazines / Q000737:chemistry
chemical_list: C445502:6-chloro-N-ethyl-1,3-5-triazine-2,4-diamine; D000538:Aluminum Silicates; D006812:Humic Substances; D012987:Soil; D014227:Triazines; C446541:deethylatrazine; D001280:Atrazine; D000077215:Clay