Abstract
In this work, the dissipation of the antibiotics doxycycline (DC) (from the group of tetracyclines), enrofloxacin (ENR) (a fluoroquinolone), and sulfamethoxypyridazine (SMP) (a sulfonamide) is investigated both under simulated sunlight and in the dark, at three different pH (4.0, 5.5, and 7.2), and in the presence of different salts and humic acids. The results indicate that all three antibiotics are very sensitive to photodegradation, and this sensitivity increased with rising pH values, from 4.0 to 7.2. The rise in pH also caused an increase in the degradation kinetic constants and a decrease in the half-lives of antibiotics. In general, the half-lives ranged from a few minutes to 6 h, depending on the pH conditions and the specific antibiotic, and followed the sequence DC > SMP > ENR, although at pH 5.5 the sequence changed to SMP > DC > ENR. After 24 h of simulated sunlight, mineralization was always lower than 10%, although the antibiotic was not quantifiable after the same time of exposure to light (24 h), which indicates that intermediate compounds were generated. The effect of the presence of salts on the dissipation of the three antibiotics was negligible for NaCl and NaNO3, while NaHCO3 did favor the dissipation of DC and ENR. The presence of humic acids showed no effect on the dissipation of SMP, and it only slightly increased the dissipation of DC and ENR. These results may be useful in the assessment of the persistence/degradation of the antibiotics studied when they reach different environmental compartments and may suffer exposure to light under different physicochemical conditions.
Highlights
Water pollution is a matter of real concern worldwide, constituting a problem that makes it clearly difficult for many human communities to have access to enough amounts of safe and quality drinking water
Among the different antibiotics, sulfamethoxypyridazine (SMP), which belongs to the group of sulfonamides, was found in concentrations that ranged between 29–149 ng L−1 in rivers of Spain [3], reaching up to 630 ng L−1 in river waters in China [4]
The three antibiotics studied (DC, ENR, and SMP) were sensitive to light, showing quite fast photodegradation kinetics, which indicates that photolysis may be an important process favoring the removal of these antibiotics from waters, both in natural water bodies and wastewater
Summary
Water pollution is a matter of real concern worldwide, constituting a problem that makes it clearly difficult for many human communities to have access to enough amounts of safe and quality drinking water. In recent decades, antibiotics spread into the environment have acquired special relevance, both from discharges related with their use in veterinary medicine and in human diseases. Different groups of these emerging pollutants have been detected in aquatic environments in a variety of countries around the world [1], with especially relevant levels found in the waters and soils of China [2]. Doxycycline (DC), a second-generation antibiotic, belonging to the tetracycline group, has been detected in concentrations of up to 47 ng L−1 in river waters in
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