Beta-lactam antibiotics, which are used extensively in human and veterinary applications, are commonly detected in surface waters. To examine how the distinct structures of different generations of beta-lactam antibiotics can influence their persistence or degradation in environmental aqueous media, we examined the fate of two penams (amoxicillin and cloxacillin) and two cephems (cephalexin and ceftriaxone) at pH 5.0 and pH 7.0. By contrast to the lack of hydrolysis of the penam antibiotics at both pHs, we observed hydrolysis of cephalexin at pH 7.0 (t_1/2 = 12 d) and ceftriaxone at pH 5.0 (t_1/2 = 2.8 d). Using high-performance liquid chromatography coupled with a diode array detector or a high-resolution mass spectrometer, we were able to confirm thiotriazinone and 3-desacetyl cefotaxime as major hydrolysis products of ceftriaxone, and propose the hydrolytic cleavage of the benzene and cephem moieties from cephalexin. In addition, we studied the effects of smectite clay particles suspended in solutions without or with dissolved organic matter. The adsorption capacity of the clay was 4- to 9-fold higher at pH 7.0 than at pH 5.0. Subsequent X-ray diffraction analysis revealed that the antibiotic adsorption was not within the clay interlayer nanopores but occurred primarily on the external clay surfaces. The addition of dissolved organic matter interfered with the adsorption of a cephem antibiotic (ceftriaxone) on the clay, but the adsorption of a penam antibiotic (amoxicillin) remained unaffected. We employed molecular modeling simulations to probe the mechanisms of adsorption on the mineral surface. Our findings offer new insights on how the compound structures can dictate different fates of the beta-lactam class of antibiotics in environmental media.

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探索β-内酰胺抗生素不同结构的命运：水解、矿物质捕获和有机物的影响

β-内酰胺抗生素广泛用于人类和兽医应用，通常在地表水中检测到。为了检查不同代 β-内酰胺抗生素的不同结构如何影响它们在环境水性介质中的持久性或降解，我们检查了两种 Penams（阿莫西林和氯唑西林）和两种头孢菌素（头孢氨苄和头孢曲松）在 pH 5.0 和 pH 值下的命运7.0. 与两种 pH 值下青霉烯类抗生素均未水解相比，我们观察到头孢氨苄在 pH 7.0 ( t _1/2 = 12 d) 和头孢曲松在 pH 5.0 ( t _1/2= 2.8 天）。使用高效液相色谱结合二极管阵列检测器或高分辨率质谱仪，我们能够确认硫代三嗪酮和 3-脱乙酰头孢噻肟是头孢曲松的主要水解产物，并提出苯和头孢烯部分的水解裂解头孢氨苄。此外，我们研究了悬浮在不含或含有溶解有机物的溶液中的绿土粘土颗粒的影响。粘土的吸附能力在 pH 7.0 时比在 pH 5.0 时高 4 到 9 倍。随后的 X 射线衍射分析表明，抗生素吸附不在粘土夹层纳米孔内，而是主要发生在粘土外表面。添加溶解的有机物会干扰头孢菌素抗生素（头孢曲松）在粘土上的吸附，但对青霉烯类抗生素（阿莫西林）的吸附不受影响。我们采用分子建模模拟来探索矿物表面的吸附机制。我们的发现为化合物结构如何决定环境介质中 β-内酰胺类抗生素的不同命运提供了新的见解。