Interaction of Imidazolinone Herbicides With Soil Humic Acids. Experimental Results and Molecular Modeling

Abstract

Adsorption and desorption isotherms of the herbicides imazapyr, imazethapyr and imazaquin on a soil humic acid have been performed at pH 2.8 and 4.0 (below and above the pKa of the herbicides). At both pH, adsorption increased according to the lipophilic character of the molecules (imazapyr Ͻ imazethapyr ϽϽ imazaquin). The extent of adsorption was higher at pH 2.8 than at pH 4.0 because of the partial ionization of the carboxylic groups of both herbicides and humic acids at increasing pH. Desorption of imazapyr and imazethapyr was nearly complete at pH 4 and higher than 60% at pH 2.8 while desorption of imazaquin was 45 and 8% at pH 4 and 2.8, respectively. No differences between adsorption isotherms at 10Њ C and 25Њ C were observed a pH 4.0 indicating that adsorption involved very weak bonds while at pH 2.8, adsorption was higher at 10Њ C than at 25Њ C indicating an exothermic process. The isosteric enthalpy of adsorption of each herbicide was low (about Ϫ1 kJoule mole Ϫ1 ) suggesting that low energetic bonds were involved. Adsorption on different humic acids has indicated that for each herbicide, the extent of adsorption expressed as K d was correlated with the amount of carboxylic and 107 ORDER REPRINTS aromatic groups of humic acids suggesting that hydrogen bonding and/or charge-transfer complexes formation could take place. Molecular modeling and geometry optimization of humic acid and soil organic matter (SOM) herbicide complexes were also performed. The results obtained with this theoretical approach gave a consistent chemical interpretation of the experimental results. To the best of our knowledge this is the first report to contribute to a better understanding of site-specific bonding of herbicides in SOM complexes by nanochemical modeling and distinct energy descriptors.

Brown Coal Derived Humate Inhibits Contact Hypersensitivity; An Efficacy, Toxicity and Teratogenicity Study in Rats

“…However the intrinsic mechanism by which it affects cellular function still needs to be clarified. It has been demonstrated that humate has a strong affinity to bind to several compounds, such as herbicides [10] and mutagens [11,12]. The possibility exists that humate adsorbs pro-inflammatory molecules such as cytokines and complement factors.…”

Effect of Sodium Humate on the Content of Trace Elements in Organs of Weaned Piglets

“…They have strong affinity for mutagens (Cozzi et al 1993), pesticides (Negre et al 2001;Li et al 2003), monoaromatic and polycyclic aromatic compounds (Nanny and Maza 2001;Kollist Siigur et al 2001), heavy metals (Livens 1991;Madronova et al 2001;Hammock et al 2003;Herzig et al 2007;Zralý et al 2008), aflatoxin B 1 (Van Rensburg et al 2006) and microorganisms (Fein et al 1999). Positive effects of oxihumolite resulting in a decreased ammonia emission in the inside environment of broiler and pig housing were noted by Suchý et al (1999) and Herzig et al (2001).…”

The effect of feed additives in pheasants fattening: A review

“…Colloidal characteristics of HA and their salts and their ability to form chelates, they can significantly modify the toxic effects of a number of xenobiotics and undesirable substances that enter the digestive tract together with feeds and water (Livens, 1991;Herzig et al, 1994). Their strong affinity to mutagens (Cozzi et al, 1993), pesticides (Negre et al, 2001;Li et al, 2003), monoaromatic and polycyclic aromatic compounds (Kollist Sügur et al, 1993;Nanny and Maza, 2001), heavy metals (Livens, 1991;Madroňová et al, 2001;Hammock et al 2003;Herzig et al, 2007), aflatoxin B1 (Van Rensburg et al, 2006) and microorganisms (Fein et al, 1999) was described. Positive effects of oxihumolite resulting in a decreased ammonia concentration in the stable environment of market broilers were obtained by Suchý et al (1999).…”