Simultaneous Adsorption of Amoxicillin, Cefuroxime and Azithromycin onto Natural Bioadsorbents: Mussel Shell, Pine Bark and Ash

The discovery of antibiotics represented an important advance, reducing significantly the mortality from infectious diseases. However, the increase in their consumption is leading to the detection of these antimicrobials in different environmental compartments, such as soils and water. Soil often serves as the primary sink for pollutants, but it can also become a source of emissions when its retention capacity is surpassed. Once these emerging contaminants reach the soil, their behaviour will depend on both the properties of the antibiotics and those of the soil. Adsorption has been recognized as a promising technique for the removal of pharmaceuticals. However, some soils have a low capacity to adsorb these contaminants, making it interesting to study the use of low-cost bioadsorbents that can enhance the adsorption capacity of these soils. Previous studies examined the capacity of mussel shell, ash, and pine bark to adsorb antibiotics such as amoxicillin, cefuroxime, and azithromycin. However, how these antibiotics behave when are present simultaneously, as they occur in the environment, has not been studied. This work studies the capacity of the three bioadsorbents mentioned before to adsorb amoxicillin, cefuroxime and azithromycin simultaneously and compare it with the data obtained in simple system (when added individually). Therefore, batch experiments were carried out by adding increasing concentrations of antibiotic (0; 2.5; 5; 10; 20; 30; 40; 50 μmol L-1) into 0.5 grams of bioadsorbent. Finally, the antibiotic concentration in equilibrium solution was measured by HPLC-UV.
The results obtained showed that when the three antibiotics were added together, ash adsorbed 100% of them, while in the simple system these percentages decreased up to 89.7%, 98.56% and 28.25% for amoxicillin, cefuroxime and azithromycin respectively. In the case of mussel shell, the opposite effect occurs, adsorption was lower when three antibiotics were added together, decreasing the percentages (when 50 μmol L-1 were added) from 48.15% to 46.86% in the case of amoxicillin, from 76.65% to 40.89% for cefuroxime and from 55.82% to 26.79% for azithromycin. Finally, in the case of pine bark, amoxicillin adsorption was
significantly higher in the ternary system (85.33%) compared to the simple system (29.38%). However, for cefuroxime and azithromycin, adsorption was higher in the simple system than in the ternary system, ranging from 58.59% to 46.68% for cefuroxime and from 36.58% to 0% for azithromycin. Adsorption data were adjusted to Linear and Freundlich model, but only mussel shell obtained a good adjustment (R2>0.9) for both models. Regarding desorption, cefuroxime and azithromycin desorption was significantly lower in ternary system than in simple system while for amoxicillin occurs the opposite, being the desorption higher in ternary system. It is observed that mussel shell exhibited desorption values below 12% in all cases, while these values reached 59% for pine bark with cefuroxime in the simple system and up to 91% for ash with azithromycin, also in the simple system. However, in ternary system, desorption is lower than 4% in most cases. In conclusion, ash was the best bioadsorbent to retain the three antibiotics simultaneously.