Sorption-desorption behavior of pesticides and their degradation products in volcanic and nonvolcanic soils: interpretation of interactions through two-way principal component analysis

Abstract

Sorption-desorption behavior of six pesticides and some degradation products was assessed on seven agricultural volcanic and nonvolcanic soils belonging to Andisol, Ultisol, Mollisol, and Alfisol orders. The global interpretation of sorption data was performed by principal component analysis. Results showed exceptionally high sorption of glyphosate and aminomethylphosphonic acid (AMPA) (the breakdown product) on volcanic soils (Kf>1500 μg1 − 1 / n mL1 / n g−1) related mainly to contents of amorphous aluminum oxides (Andisols) and crystalline minerals (Ultisols). The lower sorption on nonvolcanic soils was associated to low organic matter contents and lack of significant minerals. Metsulfuron-methyl and 3,5,6-trichloro-2-pyridinol (metabolite of chlorpyrifos) were weakly to substantially sorbed on Andisols and Ultisols, but the first one was not sorbed at pH>6.4, including nonvolcanic soils. The metabolite of diazinon, 2-isopropyl-4- methyl-6-hydroxypyrimidine, was weakly sorbed on all soils (Kf=0.4 to 3.6 μg1 − 1 / n mL1 / n g−1). Acidic compounds would be lixiviated in Mollisols and Alfisols, but they could leach also inAndisols and Ultisols if they reach greater depths. Atrazine and deethylatrazine sorption was related to organic carbon content; therefore, they were weakly retained on nonvolcanic soils (Kf=0.7 to 2.2 μg1 − 1 / n mL1 / n g−1). Chlorpyrifos was highly sorbed on all soils reaching KOC values of >8000. Finally, the significant retention of chlorothalonil and diazinon on Mollisols and Alfisols in spite of their low OC contents showed the contribution of clay minerals in the sorption process.