Effect of humic acids on the adsorption of paraquat by goethite

Interactions Between Ionic Pesticides and Model Systems for Soil Fractions

“…Although there is a lack of experimental evidence for the availability of surface sites on the coated mineral oxide to support these results, it appears that the SOM coating on the goethite particles produces a significant reduction in the number of surface sites available to interact with MCPA. As already mentioned, the interaction between PQ and bare goethite at acidic pH is almost negligible, whereas significant adsorption is observed on HA-coated goethite (Figure 2b), which is also consistent with the results reported by Brigante et al (2010). Taking into account the favourable electrostatic interactions between SOM and cationic pesticides, the adsorption of PQ on HA-coated goethite appears to take place by direct binding to the HA molecules adsorbed onto goethite particles.…”

“…At the same time, the decrease in PQ binding produced as the ionic strength increases is a consequence of the screening effect produced by the inert electrolyte on the electrostatic interaction between species of opposite charge. Similar results have previously been reported (Narine and Guy, 1982;Pacheco et al, 2003;Brigante et al, 2010), suggesting that the binding of PQ to SOM samples may be explained by an electrostatic interaction. A comparison of the behaviour of HA and peat soil as regards PQ binding is shown in Figure 2a.…”

“…This mineral has a relatively high surface area, is very reactive (Cornell and Schwertmann, 1996) and therefore plays an important role in the migration of cations and anions in natural environments. Its properties have been studied in great detail in recent years, and there is therefore abundant information about its structure, chemical properties and adsorption, which facilitate the study of its interactions with ionic herbicides (Cornell & Schwertmann, 1996;Antelo et al, 2005;Brigante et al, 2010). Ionic pesticides may interact with reactive sites on the mineral surface via electrostatic interactions, cation exchange reactions and surface binding reactions, so that a high degree of adsorption might take place on mineral surfaces.…”

“…Paraquat (PQ) is applied as a dichloride or dibromide salt, which when dissolved in water releases the organic cation PQ 2+ , which can be adsorbed on the soil surface, either by replacing inorganic cations or by an ionic interaction mechanism with negatively charged sites on the soil surface, in which the electrostatic effect will be determinant (Narine & Guy, 1982). PQ adsorbs on humic substances and the degree of adsorption increases as the pH increases, as a result of the progressive ionization of the acid groups in the organic matter (Iglesias et al, 2009;Brigante et al, 2010). PQ shows affinity for iron oxides and clay minerals (Clausen & Fabricius, 2001;Seki & Yurdakoç, 2005;Pateiro-Moure et al, 2010).…”

Use of Biomass Ashes in Agriculture with Reference to Farming Practices in Vidarbha, Maharashtra, India

“…According to European standards, the maximum allowable concentration of individual pesticides (including paraquat) in drinking water and surface water is 0.1 g/l and 1-3 g/l respectively 12 . In earlier studies, natural adsorbents such as activated bleaching earth, laponite, goethite, waste coffee grounds, activated clay, regenerated clay mineral, clays, and organo clays (sepiolite, bentonite, or illite) were used for paraquat removal [13][14][15][16][17][18][19] . To the best of our knowledge, ashes have not yet been explored as adsorbents for paraquat removal.…”