The residues of tetracycline in environment have raised increasing concern for the deleterious impact on ecological and human health. Natural organic matter (NOM), ubiquitous in natural waters, is unavoidable to encounter tetracycline, which might affect the fate of tetracycline in aquatic environment. In this study, we investigated the effect of natural organic matter (NOM) on the photolytic fate of tetracycline (TC). The photolysis kinetics of TC were evaluated with two representative NOM, tannic acid (TA) and gallic acid (GA). The presence of TA and GA obviously inhibited the removal of TC under UV irradiation with photolysis rate constant at 0.067 h^-1 and 0.071 h^-1, respectively, which were 32.3% and 28.3% less than that without TA and GA (0.099 h^-1). Furthermore, NOM exhibited different impacts on both indirect photolysis and direct photolysis. NOM promoted the formation of hydroxyl radical, induced the generation of triplet-excited state NOM and thus greatly enhanced the indirect photolysis of TC. However, direct photolysis was almost completely inhibited by NOM via inner filter effect and interacting with TC to form ground-state complex with low photoreactive. Moreover, similar intermediates were detected in the presence and absence of NOM, indicating that NOM exhibited limited influence on the degradation pathways of TC. This study reveals the multiple roles of NOM on tetracycline photolysis, contributing to better understand the photolytic fate of antibiotics in natural waters.

环境中四环素的残留已引起越来越多的关注，因为它们对生态和人类健康具有有害影响。天然水无处不在的天然有机物（NOM）不可避免地会遇到四环素，这可能会影响四环素在水生环境中的命运。在这项研究中，我们调查了天然有机物（NOM）对四环素（TC）光解命运的影响。TC的光解动力学用两种代表性的NOM：鞣酸（TA）和没食子酸（GA）进行了评估。TA和GA的存在明显抑制了紫外线照射下TC的去除，光解速率常数分别为0.067 h ^-1和0.071 h ^-1，分别比不使用TA和GA（0.099 h-）时减少了32.3％和28.3％^{。 1个}）。此外，NOM对间接光解和直接光解均表现出不同的影响。NOM促进了羟基自由基的形成，诱导了三重激发态NOM的生成，从而大大增强了TC的间接光解。然而，直接光解几乎被NOM通过内部过滤作用完全抑制，并与TC相互作用形成低光反应性的基态复合物。此外，在存在和不存在NOM的情况下都检测到类似的中间体，这表明NOM对TC的降解途径的影响有限。这项研究揭示了NOM在四环素光解中的多种作用，有助于更好地了解天然水中抗生素的光解命运。