The Interaction of Paraquat With Soil: Adsorption by an Expanding Lattice Clay Mineral

Abstract

Summary. Some characteristics of the interaction of paraquat with a dioctahedral montmorillonite have been studied by a combination of adsorption, radioisotope exchange, and X‐ray diffraction techniques. The clay exhibited a high affinity for paraquat, since when less than 50 me/100 g were absorbed no paraquat was detected in the solution (<0·07 ppm), irrespective of the saturating cation, and in the presence or absence of 3·5 M ammonium nitrate solution. Interlamellar adsorption of paraquat was detected by the occurrence, even in an aqueous environment, of the 12·6 A c‐spacing associated with the adsorption of pyridinium ions. When 14C‐labelled paraquat was added to a clay containing less than 50 me/100 g of adsorbed paraquat, complete self‐exchange was observed within 24 hr. Therefore at all levels of adsorption, paraquat held in the adsorbed phase must be in equilibrium with a solution concentration. Interaction entre le paraquat et le sol; adsorption par un mineral argileux gonflant Résumé. Quelques caractères de l'interaction entre le paraquat et une montmorillonite dioctahèrique ont étéétudiés par une combinaison des techniques suivantes: adsorption, échanges de radioisotopes et diffraction des rayons X. L'argile manifesta une grande affinité pour le paraquat: lorsque moins de 50 me/100 g furent absorbés, le paraquat ne fut plus décelé cans la solution (<0.07 ppm), indépendamment du cation saturant, et en présenee ou non d'une solution 3,5 M de nitrate d'ammonium. L'adsorption interlamellaire du paraquat fut détectée par l'occurence, même dans un environnement aqueaux, d'un espacement selon l'axe c de 12,6 A associé avec l'adsorption d'ions pyridinium. Quand du paraquat marqué au 14C fut ajoutéà une argiie contenant moins de 50 me/100 g de paraquat adsorbé, un autoéchange complet fut observé dans les 24 heures. En conséquence, á tous les niveaux d'adsorption, le paraquat retenu dans la phase adsorbée doit être en êquilibre avec une concentration de la solution. Die Wechselwirkung zwischen Paraquat und Boden: Adsorption an ein aufweit‐bares Schichtgitter‐Tonmineral Zusammenfassung. Mit Hilfe einer Kombination von Adsorptions‐ und Radio‐isotopenaustauschtechniken und Röntgenstrukturanalyse wurden einige Charakteristika der Wechseiwirkungen zwischen Paraquat und einem diocatedrischen Montmorillonit untersucht. Der Ton besass eine hohe Affinität fur Paraquat, da in der Lösung kein Paraquat mehr nachzuweisen war (<0,07 ppm), wenn weniger als 50 mval/100 g adsorbiert worden waren. Dies war sowohl von dem entsprechenden Kation als auch von der Anwesenheit oder Abwesenheit einer 3,5 M Ammoniumnitratlosung unabhangig. Interlamellare Adsorption von Paraquat wurde anhand der sogar in wassrigem Milieu stattfindenden C‐Aufweitung (12,6 Å), verbunden mit einer Adsorption von Pyridiniumionen, festgestellt. Wurde 14C‐markiertes Paraquat einem Boden, der weniger als 50 mval/100 g adsorbiertes Paraquat enthielt, zugegeben, so trat innerhalb von 24 Stunden vollkommener Selbstaustausch ein. Das adsorbierte Paraquat muss dah...

Interaction of Btpyridylium Herbicides With Organo‐clay Complex

“…While paraquat was adsorbed by montmorillonite in amounts approximately equal to the CEC of the clay, the amounts of diquat adsorbed were slightly less than the CEC. In general, the data are in accordance with those reported by other workers on the adsorption of diquat and paraquat by montmorillonite (Weber and Weed, 1968;Weed and Weber, 1969;Knight and Denny, 1970;Damanakis et al, 1970). The adsorption of the two herbicides by the organo-clay complex followed nearly the same pattern as was observed for the pure clay, but the amounts adsorbed by the former on 'per unit weight basis' were considerably lower than the latter.…”

Interaction of Humic Substances With Bipyridylium Herbicides

“…During the past few years much work has been published on the adsorption of diquat and paraquat by mineral soils, clays, and charcoal (Calderbank 1968;Damanakis et al 1970;Faust and Zarins 1969; Knight and Denny 1970;Weber et al 1965;. However, little is known about the interaction of bipyridylium herbicides with humic substances, the principal organic components of soils and waters.…”

Fate and Behavior of Fungicide Guazatine in Soils

“…Thus it is concluded that guazatine was preferentially adsorbed by soil inorganic fraction, and this is quite similar to bipyridinium herbicides. 6,11,[14][15][16] Predominant mechanism for the adsorption of guazatine to soil is considered to be an ion exchange, since the pKa values of guanidine and imino groups of the fungicide are greater than 13 and 9, respectively; consequently the fungicide is regarded as existing predominantly as a trivalent cation in neutral environment. It can be satisfactorily explained by this mechanism that guazatine was adsorbed to Chiba soil to the extent of normal CEC.…”