title: Reactivity of the plant growth regulator paclobutrazol (cultar) with two tropical soils of the northeast semiarid region of Brazil.
abstract: The reactivity of paclobutrazol (PBZ, a plant growth retardant) with a Yellow Ultisol and a Vertisol from the semiarid northeast region of Brazil was evaluated through batch sorption experiments and modeling. Although not instantaneous, the sorption kinetic of PBZ (pure and formulated) was fast (a few hours) in both soils. The sorption kinetics were well described by a second-order (dS(t)/dt=k(2)(S(e2)-S(t))(2)) but not by a first-order model. The sorption isotherms were found to be linear and the calculated K(D) values were 8.8 +/- 0.11 and 7.4 +/- 0.2 L kg(-1) for pure PBZ in the Ultisol and the Vertisol, respectively. The corresponding K(OC) values were 1275 +/- 34 (logK(OC) = 3.11) and 1156 +/- 49 (logK(OC) = 3.06) L kg(-1), respectively. Considering the very different texture of the two soils and the similar K(OC) values determined, these results showed that in both soils, the sorption of PBZ is dominantly controlled by organic matter, although some interactions of PBZ with iron oxides (goethite) were observed in the Ultisol. Based on these sorption parameters a low leachability potential of PBZ in soils is anticipated, as they correspond to a groundwater ubiquity score (GUS) ranging from 2.0 to 2.7, i.e., moderately to not mobile, in contradiction with the actual groundwater situation in Brazil. This work stresses the need to evaluate and predict the risk associated with aquifer contamination by this widely used plant growth regulator.
authors.affiliation: Departamento de Energia Nuclear, Universidade Federal de Pernambuco, Av. Prof. Luiz Freire 1000, Cid. Universitária, CEP 54740-540, Recife, PE, Brazil.
authors.forename: Mônica Lúcia
authors.initials: ML
authors.lastname: Milfont
authors.forename: Jean Manuel Fonseca
authors.initials: JM
authors.lastname: Martins
authors.forename: Antonio Celso Dantas
authors.initials: AC
authors.lastname: Antonino
authors.forename: Ester Ribeiro
authors.initials: ER
authors.lastname: Gouveia
authors.forename: André Maciel
authors.initials: AM
authors.lastname: Netto
authors.forename: Véronique
authors.initials: V
authors.lastname: Guiné
authors.forename: Hélène
authors.initials: H
authors.lastname: Mas
authors.forename: Maria Betânia Galvão
authors.initials: MB
authors.lastname: dos Santos Freire
mesh_terms: D000327:Adsorption; D001938:Brazil; D002244:Carbon / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009584:Nitrogen / Q000032:analysis; D010316:Particle Size; D010937:Plant Growth Regulators / Q000737:chemistry*; D018570:Risk Assessment; D012987:Soil / Q000032:analysis; D012989:Soil Pollutants / Q000737:chemistry*; D014230:Triazoles / Q000737:chemistry*; D014329:Tropical Climate; D014876:Water Pollution
chemical_list: D010937:Plant Growth Regulators; D012987:Soil; D012989:Soil Pollutants; D014230:Triazoles; C053370:paclobutrazol; D002244:Carbon; D009584:Nitrogen