Insights into tetracycline adsorption onto kaolinite and montmorillonite: experiments and modeling

Abstract

Adsorption of tetracycline (TC) on kaolinite and montmorillonite was investigated using batch adsorption experiments with different pH, ionic strength, and surface coverage. As a result, pH and ionic strength-dependent adsorption of TC was observed for the two clay minerals. The adsorption of TC decreased with the increase of pH and ionic strength, and high initial TC concentration had high adsorption. In addition, a triple-layer model was used to predict the adsorption and surface speciation of TC on the two minerals. As a result, four complex species on kaolinite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), ≡SOH(0)∙H2TC(±), and ≡SOH(0)∙HTC(-)) and three species on montmorillonite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), and ≡SOH(0)∙HTC(-)) were structurally constrained by spectroscopy, and these species were also successfully fitted to the adsorption edges of TC. Three functional groups of TC were involved in these adsorption reactions, including the positively charged dimethylamino group, the C=O amide I group, and the C=O group at the C ring. Combining adsorption experiments and model in this study, the adsorption of TC on kaolinite and montmorillonite was mainly attributed to cation exchange on the surface sites (≡X(-)) compared to surface complexation on the edge sites (≡SOH) at natural soil pH condition. Moreover, the surface adsorption species, the corresponding adsorption modes, and the binding constants for the surface reactions were also estimated.

Fate of tetracycline antibiotics in dairy manure-amended soils

“…The strong correlation between TC sorption and effective cation exchange capacity could result from electrostatic attraction between the tertiary amine group that is positively charged at environmentally relevant soil pHs and the negatively charged clay surface (Jones et al 2005;Zhao et al 2015). As this study also found a strong positive correlation between K d and Mg 2+ , Ca 2+ , and Na + , cation bridging between negatively charged functional groups and base cations may contribute to the strong interaction be-tween TCs and smectite clays (Figueroa et al 2004).…”

“…Sorption of TCs to montmorillonite and kaolinite clays depends on solution pH, ionic strength, and organic matter content (Figueroa et al 2004;Avisar et al 2010;Zhao et al 2011Zhao et al , 2015. Estimating TC sorption in soils based on K d values attained from research with pure clay minerals may be misleading, since clay surfaces in actual soils may be coated with organic matter or metal oxides, thus affecting antibiotic sorption to the clay surface.…”

“…Although the net charge of the TC zwitterion is zero, this species contributes significantly to total TC sorption to soil clays because it is the dominant TC species at the common soil pH values of between approximately 3.3 and 8. In addition to the dominant sorption mechanism of cation exchange which predominates on kaolinite surface sites (Zhao et al 2015), surface complexation via H-bonding is responsible for TC sorption to kaolinite edge sites (Li et al 2010;Zhao et al 2015). The size and physical conformation of TC aligned with the kaolinite surface does not appear to influence sorption, but rather charge density shows the greatest effect (Li et al 2010).…”

Transport of Potential Manure Hormone and Pharmaceutical Contaminants through Intact Soil Columns

“…Oxytetracycline was identified at the limit of detection in leachate of only two of the five treatment columns. No other tetracycline antibiotics were found in column leachate even though the relatively high pH of our soils promotes deprotonation and development of a negative charge that leads to weaker soil sorption (Peng et al, 2014; Zhao et al, 2015). In a similar soil column experiment (diameter = 25 cm, length = 60 cm), investigators did not detect oxytetracycline in the leachate after 4.2 mg was applied to each column (Kay et al, 2005a).…”

Effect of Soil Solution pH during the Tetracycline Intercalation on the Structural Properties of a Dioctahedral Smectite: Microstructural Analysis

“…Several studies, in relation to the use of montmorillonite in the pharmaceutical-sediment interaction context, have been, recently, realized [18][19][20][21][22][23][24][25][26][27].…”