Clarithromycin and Tetracycline Binding to Soil Humic Acid in the Absence and Presence of Calcium

Abstract

Numerous ionizable organic micropollutants contain positively charged moieties at pH values typical of environmental systems. Describing organic cation and zwitterion interaction with dissolved natural organic matter requires explicit consideration of the pH-dependent speciation of both sorbate and sorbent. We studied the pH-, ionic strength-, and concentration-dependent binding of relatively large, organic cations and zwitterions (viz., the antibiotics clarithromycin and tetracycline) to dissolved humic acid in the absence and presence of Ca 2+ and evaluated the ability of the NICA-Donnan model to describe the data. Clarithromycin interaction with dissolved humic acid was well described by the model including the competitive effect of Ca 2+ on clarithromycin binding over a wide range of solution conditions by considering only the binding of the cationic species to low proton-affinity sites in humic acid. Tetracycline possesses multiple ionizable moieties and forms complexes with Ca 2+ . An excellent fit to experimental data was achieved by considering tetracycline cation interaction with both low and high protonaffinity sites of humic acid and zwitterion interaction with high proton-affinity sites. In contrast to clarithromycin, tetracycline binding to humic acid increased in the presence of Ca 2+ , especially under alkaline conditions. Model calculations indicate that this increase is due to electrostatic interaction of positively charged tetracycline-Ca complexes with humic acid rather than due to the formation of ternary complexes, except at very low TC concentrations.

The Effect of Clarithromycin Toxicity on the Growth of Bacterial Communities in Agricultural Soils

“…Clarithromycin speciation is strongly pH dependent, occurring predominantly in cationic form at soil pH values (4.1 to 6.1) [76]. Since soil charge is pH dependent and the negative charge increased with pH [77,78], clarithromycin adsorption in the soil may increase with pH, as described previously for humic substances [79]. This behavior is consistent with the results obtained in this study, showing that the increase in pH values may reduce the toxicity that clarithromycin exerts on the growth of soil bacterial communities.…”

Cation–Pi Interaction: A Key Force for Sorption of Fluoroquinolone Antibiotics on Pyrogenic Carbonaceous Materials

“…This mechanism can also apply to amino acids interacting with aromatic moieties and is considered to be important for adjusting the acid–base balance in organisms. Cation–pi interactions may be ubiquitous for antibiotics sorption, as evidenced by the competition between Ca 2+ and clarithromycin on low proton-affinity sites in humic acids, and the 2.32 times higher desorption of CIPs from graphite when the sodium concentration increased from 0.01 mol/L to 0.45 mol/L (Figure ). Antibiotics behavior and risk should be carefully evaluated considering the ionic strength change, especially in estuaries, for ionic antibiotics binding with PCMs, which are ubiquitous in the environment …”

The role of soil components in the sorption of tetracycline and heavy metals in soils

“…31 Specically, HA, a subset of natural organic matter, could mainly interact with TC, thus promoting the complex formation of a monoacid with discrete sites. 14,32 Differently, the sorption of TC on clay mineral was dependent on TC solution chemistry. Cation exchange was the most important mechanism for cation species, whereas, surface complexation mechanism was important for zwitterion species.…”