Tetracycline adsorption on kaolinite: pH, metal cations and humic acid effects

Abstract

Contamination of environmental matrixes by human and animal wastes containing antibiotics is a growing health concern. Because tetracycline is one of the most widely-used antibiotics in the world, it is important to understand the factors that influence its mobility in soils. This study investigated the effects of pH, background electrolyte cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), heavy metal Cu(2+) and humic acid (HA) on tetracycline adsorption onto kaolinite. Results showed that tetracycline was greatly adsorbed by kaolinite over pH 3-6, then decreased with the increase of pH, indicating that tetracycline adsorption mainly through ion exchange of cations species and complexation of zwitterions species. In the presence of five types of cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), tetracycline adsorption decreased in accordance with the increasing of atomic radius and valence of metal cations, which suggested that outer-sphere complexes formed between tetracycline and kaolinite, and the existence of competitor ions lead to the decreasing adsorption. The presence of Cu(2+) greatly enhanced the adsorption probably by acting as a bridge ion between tetracycline species and the edge sites of kaolinite. HA also showed a major effect on the adsorption: at pH < 6, the presence of HA increased the adsorption, while the addition of HA showed little effect on tetracycline adsorption at higher pH. The soil environmental conditions, like pH, metal cations and soil organic matter, strongly influence the adsorption behavior of tetracycline onto kaolinite and need to be considered when assessing the environmental toxicity of tetracycline.

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

“…The preparation of sorbents was conducted according to the previous study (Zhao et al 2011). The specific surface area of kaolinite and montmorillonite was 22.3 and 46.0 m 2 g −1 .…”

Tetracycline: production, waste treatment and environmental impact assessment

“…Generally, tetracyclines, behave positive (pH <3.3), neutral (3.3 <pH <7.68) or negative (pH > 7.68) (Zhao et al, 2011b). The tetracyclines are strong chelating agents and pH dependent, and they have their antibacterial activity and pharmacokinetics decreased when associated with foods rich in calcium, iron, magnesium and other minerals or antacids such as sodium bicarbonate, which increase the pH in the stomach.…”

“…Residues of antibiotics, including tetracyclines from Wastewater Treatment Plants (WWTPs) of urban and agricultural effluents are frequently detected in surface water, groundwater, soils and sediments (Zhao et al, 2011b).…”

“…Generally, they are present in relatively low concentrations (ng or mg per L), below the threshold levels to show the effects of medicinal treatment on bacterial populations and other exposed species (Boxall et al, 2003;Zhao et al, 2011b).…”

Oxytetracycline sorption onto Iraqi montmorillonite

“…Few authors have reported the effect of iron on the extent of adsorption of antibiotics onto clay minerals (Campbell and Hasinoff 1991;Zhao et al 2011). To study this effect for Iraqi montmorillonite, the concentration of the available iron in the montmorillonite was determined with ICP-MS and found to be 252 lg g 21 (0.0045 mmol Fe g -1 ).…”