Effects of colloidal manure DOM on the transport of antibiotics in calcareous soils

Colloids in the environment are defined as suspended particles in the size range of 1 nm to 10 microns. Both organic matter and antibiotics leached from animal manures applied to farmland may pose a pollution risk of groundwater. Manure colloids, which are mainly composed of dissolved organic matter (DOM), have been known to play an important role in facilitating transport of various strongly-sorbing contaminants in subsurface environments. Research on co-transport behavior of manure colloid DOM and antibiotics is lacking. In the present study, the effects of colloidal DOM derived from pig manure and chicken manure on the transport of different antibiotics were examined in a cropland soil and an orchard soil. According to the breakthrough curves obtained for repacked soil columns (2.5 cm in diameter, 15 cm in height) under a simulated rainfall intensity of 20 mm/h, florfenicol was highly mobile and leached out almost simultaneously with the water flow tracer Br^– for the cropland soil, which exhibited an 11%-23% higher leaching capacity than for the orchard soil. On the other hand, norfloxacin and tylosin did not penetrate through the column and most of their residues were retained in the top soil layer. Pig manure DOM delayed the breakthrough of florfenicol by 0.07-0.13 pore volume and increased its residues by 15%-26% as a result of enhanced retention through a co-sorption mechanism, and similar effects of chicken manure DOM were observed.