Ciprofloxacin and tetracycline are antibiotics widely used by human and animals, which enter soil through reclaimed water irrigation and biosolid land application. Soil composition, such as soil organic matter, colloids, and metal oxides, may influence the fate and transport of antibiotics in the subsurface environment. Our experimental studies show that ciprofloxacin cannot break through soil columns regardless of presence and absence of Fe-oxides and humic acids. However, the high sorption of ciprofloxacin on soil colloids (Kd~10<sup>4-5</sup> L/kg) favors its breakthrough from the soil. This colloid-facilitated effect becomes more significant at lower ionic strength of solution. Compared to ciprofloxacin, tetracycline has a higher mobility in the soil, but colloid-facilitated effect is limited because of its lower sorption on soil colloids (Kd~10<sup>3-4</sup> L/kg). The transport of tetracycline is negatively correlated with the contents of Fe-oxides and organic matter. The recovery rates of tetracycline decreased from 35.38% to 11.95% and from 35.38% 0.01% when the proportions of soil surfaces coated by Fe-oxides and humic acids increased from 0 to 50%, respectively. The results show that the mobility of dissolved and colloid-bound tetracycline respond oppositely to the change in solution ionic strength, making the net effect of soil colloids on tetracycline transport vary with soil solution chemistry. These results imply that colloid-mediated interactions of antibiotics with soil surfaces and solution chemistry largely determine their off-site environmental risks.

Colloid-mediated transport of antibiotics through chemically heterogeneous porous media

2019 Spring National Meeting

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