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Atrazine, Isoproturon, Mecoprop, 2,4‐D, and Bentazone Adsorption onto Iron Oxides
Author(s) -
Clausen Liselotte,
Fabricius Ida
Publication year - 2001
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2001.303858x
Subject(s) - ferrihydrite , mecoprop , adsorption , chemistry , goethite , lepidocrocite , atrazine , ionic strength , inorganic chemistry , humic acid , nuclear chemistry , pesticide , environmental chemistry , aqueous solution , organic chemistry , mcpa , fertilizer , agronomy , biology
Iron oxides are important components influencing the adsorption of various inorganic and organic compounds in soils and sediments. In this study the adsorption on iron oxides of nonionic and ionic pesticides was determined as a function of solution pH, ionic strength, and pesticide concentration. The investigated iron oxides included two‐line ferrihydrite, goethite, and lepidocrocite. Selected pesticides comprised atrazine (6‐chloro‐ N 2 ‐ethyl‐ N 4 ‐isopropyl‐1,3,5‐triazine‐2,4‐diamine), isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethylurea)], mecoprop [( RS )‐2‐(4‐chloro‐2‐methylphenoxy)propionic acid], 2,4‐D (2,4‐dichlorophenoxyacetic acid), and bentazone [3‐isopropyl‐1 H ‐2,1,3‐benzothiadiazin‐4‐(3 H )‐one 2,2‐dioxide]. The adsorption of the nonionic pesticides (atrazine and isoproturon) was insignificant, whereas the adsorption of the acidic pesticides (mecoprop, 2,4‐D, and bentazone) was significant on all investigated iron oxides. The adsorption capacity increased with decreasing pH, with maximum adsorption reached close to the p K a values. The addition of CaCl 2 in concentrations from 0.0025 to 0.01 M caused the adsorption capacity to diminish. The adsorption of bentazone was significantly lower than the adsorption of mecoprop and 2,4‐D, illustrating the importance of a carboxyl group in the pesticide structure. The adsorption capacity on the iron oxides increased in the order: lepidocrocite < goethite < two‐line ferrihydrite. The maximum adsorption capacities of mecoprop and 2,4‐D on goethite were found to be equivalent to the site density of singly coordinated hydroxyl groups on the faces of the dominant {110} form, suggesting that singly coordinated hydroxyl groups are responsible for adsorption. Differences in adsorption capacities between iron oxides can be explained by differences in the surface site density of singly coordinated hydroxyl groups. The maximum measured adsorption capacity of mecoprop on two‐line ferrihydrite was equivalent to 0.2 mol/mol Fe.