## 3 Endocrine-Disrupting Compounds EDCs
### Antibiotic Degradation
Benzene on SMX could be directly hydroxylated to form product 3, and the double bond on the isoxazole ring was added by hydroxylation to form product 4. EB-induced cleavage of the S-N bond may have led to the formation of intermediates 5, 6, and 7; meanwhile, further hydroxylation of product 5 may have produced product 9, and hydrogen-substituted hydroxyl on the aniline of product 7 may have produced product 8. When the amino group in benzene and the methyl group in isoxazole are oxidized to  
Figure 9: Potential degradation pathways of SMX within EB irradiation process [118]. nitro and carboxyl groups, respectively, substances 10 and 11 may be formed. In particular, substance 12 is the result of further hydroxylation of sub-substance 11. Toxicity measurements carried out with the use of luminescent bacteria showed that the use of an electron beam will significantly reduce the toxicity of sulfonamides in relation to aquatic ecosystems. Similar observations were reported by Kim et al. [119]; for an aqueous solution of sulfamethazine with an initial concentration of 30 mg dm\({}^{-3}\) after a dose of 2 kGy, the toxicity to green algae decreased sevenfold. The results indicate that the \({}^{\bullet}\)OH radical plays a dominant role in the degradation of sulfonamide group antibiotics. Much better results were obtained for tetracycline and limomycin, for which a 53- and 37-fold decrease in toxicity, respectively, were observed under the same conditions. Radiation technologies have also been successfully used to remove residues of other types of antibiotics including \(\beta\)-lactams (amoxicillin, cefradine) [34; 35], as well as other antibiotics (linomycin and tetracycline) [22; 34; 36; 119; 120]. It has also been shown that by using an electron beam to utilize medical intravenous infusion bottles, satisfactory results can be obtained for the degradation of amoxicillin, ofloxacin, and cefradine [35] (see Table 1). The use of an electron beam for tetracycline degradation in artificially contaminated pig manure also provided satisfactory results [36]. The degradation efficiency under gamma irradiation for the group of antibiotics tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC) was investigated in different matrices [120]. It has been shown that degradation is lowest in an acidic environment, pH = 2, slightly increases from pH 4 to 8, and decreases at pH = 10. The addition of H\({}_{2}\)O\({}_{2}\) (1-5 \(\upmu\)mol) to the irradiation increased the degradation efficiency. The presence of free radical scavengers Cl\({}^{-}\), CO\({}_{3}\)\({}^{2-}\), NO\({}_{3}\)\({}^{-}\), NO\({}_{2}\)\({}^{-}\), and humic acid had an effect on TC degradation, which was higher at low concentrations of Cl\({}^{-}\), CO\({}_{3}\)\({}^{2-}\), and humic acid and significantly decreased at low concentrations of NO\({}_{3}\)\({}^{-}\) and NO\({}_{2}\)\({}^{-}\). The significantly reduced process efficiency in the presence of electron scavengers (NO\({}_{3}\)\({}^{-}\) and NO\({}_{2}\)\({}^{-}\)) indicates that TC degradation occurs by both oxidation and reduction, with reduction predominating. In the range of applied doses, it was not possible to achieve complete mineralization, but the formed degradation products were characterized by lower toxicity than the initial substances. In the case of fluoroquinolone antibiotics, i.e., norfloxacin and ciprofloxacin, gamma radiation also provided satisfactory results (Table 1) [37]. To achieve 40% mineralization, a dose of 6 kGy must be applied to the system. Acute toxicity determined with _Vibrio fischeri_ bacteria showed increased toxicity at low doses, indicating that the early degradation products are more toxic than the starting molecules. The results of biodegradation experiments carried out in activated sludge showed that the degradation products became available for the metabolic processes of microorganisms. One of the widely used antibiotics is ornidazole (ORZ), a synthetic nitroimidazole used to treat infections caused by both anaerobic bacteria and protozoa.