Abstract
Cephalexin (CEX) is an antibiotic commonly used to treat bacterial infections in humans and animals. However, it is also a micropollutant. Thus, this study evaluated the degradation of CEX using ultraviolet irradiation (UV-C) and analyzed the by-products as well as their residual antimicrobial activity. A reactor with a mercury vapor lamp was used for the degradation. Irradiated CEX solutions were collected over a period of 4 hours and analyzed using high-performance liquid chromatography coupled with mass spectrometry. For the residual antimicrobial activity the susceptibility test was performed using Staphylococcus aureus and Escherichia coli microorganisms by broth microdilution. It was found that CEX, after treatment, generated a metabolite with a mass of 150 m/z in 15 min. A four- and eightfold increase in the minimum inhibitory concentration of the drug against S. aureus and E. coli could be observed, respectively, after 20 min. Therefore, this treatment proved to be effective in the degradation of CEX, being able to degrade 81% of the initial molecule of the drug in 20 min. Furthermore, the antimicrobial activity of the CEX solution decreased as the irradiation time increased, indicating loss of antimicrobial function of the initial CEX molecule and the resulting by-products.
Highlights
In the last decades, industrial expansion and population growth have directly contributed to the increase in the pollution of the aquatic environment
Low pressure (LP) mercury lamps emit monochromatic radiation in wavelengths of less than 254 nm, with extensive UV-C flux, so they are often used in AOPs, because this wavelength range is responsible for the production of ⋅OH and ⋅H radicals, which enhance the decomposition of organic contaminants (He et al ; Lastre-Acosta et al ; Paniagua et al ) The reactor (Figure 2) was kept in an ice bath during analysis in order to cool the system and avoid analyte degradation by sources other than radiation
Ultraviolet irradiation (UV254nm) can degrade innumerable organic pollutants through direct photolysis, as some of these compounds are capable of absorbing photons, which leads to high molecular excitation and subsequent cleavage of bonds and chemical transformation (Carena et al )
Summary
Industrial expansion and population growth have directly contributed to the increase in the pollution of the aquatic environment. Studies have reported a new class of emerging contaminants called micropollutants (Harb et al ). They are found in very low concentrations in nature (microgram/litre – μg.LÀ1 and nanogram/litre – ng.LÀ1), and their effects on the environment and human health are still poorly understood. Antibiotics are drugs capable of stopping or inhibiting the growth of many microorganisms and occupy a significant portion of the total drugs available for commercialization. They are very frequently prescribed to treat infections in humans, and are routinely used in and livestock rearing (Guzmán-Trampe et al ). These contaminants have become a growing environmental problem, alarming researchers because of their increased ability to perpetuate and spread genes of antimicrobialresistant bacteria (Kumar et al ), besides causing environmental imbalance and anomalies to several aquatic species (Wang et al )
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