Sorption of Lincomycin at Low Concentrations from Water by Soils

Lincomycin is one of the most frequently detected antibiotics in the soil and water environments. A better understanding of lincomycin sorption by soil is beneficial for assessing its environmental fate, transport, and potential impacts to human and ecosystem health. Systematic batch studies were conducted to characterize sorption of lincomycin by soils with aqueous concentrations at microgram per liter levels. The effects of solution pH, background salt composition, and ionic strength on lincomycin sorption were evaluated. Cation exchange is the primary mechanism for lincomycin sorption by soils. Lincomycin is more competitive for cation exchange sites occupied by K+ than Ca2+. The presence of K+ and Ca2+ in aqueous solution (0.02 mol L-1) significantly suppressed lincomycin sorption, with more suppression observed for the soils with lower cation exchange capacity. A CaCl2 solution manifested a more suppressive effect on lincomycin sorption than KCl, plausibly because the acidic functional groups in soil organic matter, such as carboxylate, form relatively stable complexes with Ca2+, leading to reduced interactions with lincomycin. Soil mineral fractions are thus believed to be the major domain for sorption of lincomycin in Ca2+-saturated soils. Lincomycin sorption increased as soil solution pH increased from 5.8 to 7.8, and then decreased significantly at pH 8.9. The maximum sorption occurred at pH values between 7.3 and 7.8, near the dissociation constant (pK(a)) of lincomycin (7.6). These results suggest that inorganic cations commonly present in water could effectively compete with trace levels of cationic pharmaceuticals for sorption sites in soils, hence altering their transport and transformation processes in the environment.