Binding of fluoroquinolone carboxylic acid derivatives to clay minerals

Large quantities of fluoroquinolone carboxylic acid (FQCA) derivatives are applied as antibacterial agents in large-scale animal husbandry. Important quantities are transported to agricultural areas by means of liquid manure. The binding of FQCA derivatives to clay minerals and their sorption by five soils from different geographic areas were investigated. Sorption was studied in batch experiments using radioactive labeled enrofloxacin (Baytril), decarboxylated enrofloxacin, ciprofloxacin (Cyprobay), levofloxacin (Oxaldin), and a fluorochloroquinolone carboxylic acid derivative. More than 90% (K-D = 260-5612) of the applied enrofloxacin adsorbed on the different soils. The other chemicals showed a similar adsorption (K-D = 285-496) on a German soil except the decarboxylated enrofloxacin (K-D = 7.7). At clay minerals enrofloxacin was adsorbed >98%. X-ray diffraction analysis showed that the adsorption at the clay mineral montmorillonite occurred between the layers, resulting in an expansion of the spacing. Microcalorimetric and infrared measurements confirmed an electrostatic interaction between the adsorbed chemical and the adsorbent.