Document Detail

Effect of pH and ionic strength on the binding of paraquat and MCPA by soil fulvic and humic acids.
MedLine Citation:
PMID:  19269671     Owner:  NLM     Status:  MEDLINE    
The effect of pH and ionic strength on the interaction between pesticides (paraquat and MCPA) and humic substances (soil extracted humic acid and fulvic acid) was interpreted with a simple electrostatic model. Potentiometric titrations were carried out, the charge curves for the humic substances were obtained for three values of ionic strength, and the parameters that define proton binding to humic and fulvic acid were calculated by application of the NICA-Donnan model. The binding isotherms were obtained for paraquat-humic acid and paraquat-fulvic acid at three different pH values and two ionic strengths, and the MCPA-fulvic acid binding isotherms for two pH values and two ionic strengths. Binding experiments were carried out by use of a membrane dialysis technique and the concentrations of pesticide were measured by HPLC. The amount of paraquat bound to the humic substances increased with pH, decreased with increasing ionic strength, decreased in the presence of Ca(2+) and was greater for humic acid than for fulvic acid. Much less binding was observed with MCPA than with paraquat, and therefore the isotherms were not well defined. The application of a simple electrostatic model enabled us to conclude that the effect of pH and ionic strength on binding of paraquat to humic substances is due to the effect that these parameters have on the humic substance charge, and the model provided an excellent reproduction of the experimental binding isotherms.
A Iglesias; R López; D Gondar; J Antelo; S Fiol; F Arce
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2009-03-09
Journal Detail:
Title:  Chemosphere     Volume:  76     ISSN:  1879-1298     ISO Abbreviation:  Chemosphere     Publication Date:  2009 Jun 
Date Detail:
Created Date:  2009-05-18     Completed Date:  2009-07-10     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0320657     Medline TA:  Chemosphere     Country:  England    
Other Details:
Languages:  eng     Pagination:  107-13     Citation Subset:  IM    
Departamento de Química Física, Facultad de Química, Universidad de Santiago de Compostela, Santiago de Compostela, Spain.
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MeSH Terms
2-Methyl-4-chlorophenoxyacetic Acid / analysis,  chemistry*
Benzopyrans / analysis,  chemistry*
Humic Substances / analysis*
Hydrogen-Ion Concentration
Models, Chemical
Osmolar Concentration
Paraquat / analysis,  chemistry*
Pesticides / analysis,  chemistry*
Soil Pollutants / analysis,  chemistry*
Reg. No./Substance:
0/Benzopyrans; 0/Humic Substances; 0/Pesticides; 0/Soil Pollutants; 4685-14-7/Paraquat; 479-66-3/fulvic acid; 94-74-6/2-Methyl-4-chlorophenoxyacetic Acid

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