将：稳定同位素法Stable Isotopes Method在地下水的相关水文研究中已得到广泛应用例如地下水污染源研究、地下水补给区识别、地下水补给源识别等2。具有相同的质子数及不同中子数的同一元素不同核素互为同位素而核素中不具放射性的同位素称之为稳定同位素。氢元素和氧元素共同构成了水分子氢元素的稳定同位素包括1H氕H、2H氘D两种形式氧元素的稳定同位素则包括16O、17O和18O三种形式。在水循

The Stable Isotopes Method has been widely used in hydrological research on groundwater, such as groundwater pollution source investigation, identification of groundwater recharge areas, and identification of groundwater recharge sources [2]. Isotopes with the same atomic number but different neutron numbers of the same element are called stable isotopes, and isotopes in which the nucleus does not have radioactivity are called stable isotopes. Hydrogen and oxygen elements together constitute water molecules, and the stable isotopes of hydrogen include two forms, 1H (protium/H) and 2H (deuterium/D), while the stable isotopes of oxygen include three forms, 16O, 17O, and 18O. In the process of water cycle, water vapor with heavier stable isotopes will be discharged first, and water with heavier stable isotopes will be enriched in the formed precipitation. Therefore, the composition of hydrogen and oxygen stable isotopes in natural water bodies will also differ depending on their spatial and temporal distribution [3,4]. Therefore, stable water isotopes (δ18O and δ2H) are considered to be powerful and flexible tools for detecting infiltration and inflow. This method can obtain different external water sources in the pipeline through inputting isotopic values (without referring to the flow rate assumption). However, the hydrological processes in the sewer system may be quite complicated. When external water flow involves two or more water sources or is the same as the drinking water source, δ18O and δ2H have significant limitations in quantitatively analyzing infiltration and inflow. Some studies have shown that the difference in stable isotopes in invaded areas should be above 0.9‰ to obtain better reliability. Therefore, it is necessary to introduce new indicators to assist in calculating the proportion of external water invasion to achieve comprehensive and stable calculation results.

Sulfur is widely present in nature, with 32S, 33S, 34S, and 36S as four stable isotopes. Among them, stable isotope 34S, due to its significant difference in content under different conditions and strong stability, has been considered for quantitatively analyzing infiltration and inflow in sewage pipelines. For example, Houhou J et al. studied the potential of stable isotopes of water (18OH2O and D) and dissolved sulfate (34S and 18OSO4) in determining the external water sources and total amount of urban drainage network in the eastern city of Nancy, France, and proved that the multi-component method can reveal the hydrological phenomena and complexity of urban sewers, affirming the effectiveness of the stable isotopes of dissolved sulfate for water source analysis [1]. Moreover, some studies have shown that the composition of dissolved sulfate isotopes in sewage is limited by microbial activity since most sewage pipes maintain relatively high oxygen content, which limits the activity of sulfate-reducing bacteria [1,5]. However, currently, there is a lack of corresponding research on the impact of different water use behaviors on sulfur stable isotopes in daily life, as different water use behaviors involve various washing products, and sulfur-containing chemicals often participate in the composition of washing products and occupy a significant proportion [6]. Studies have found that the internal components of washing products such as laundry detergent, dishwashing liquid, soap, shower gel, etc., usually involve sodium alkyl sulfate, fatty alcohol polyoxyethylene ether sulfate, etc. [7]; the internal components of hair care products such as shampoo, conditioner, etc., usually involve sodium lauryl sulfate, fatty alcohol sulfate, etc. [8]; the internal components of face wash usually involve alkyl sulfate, sulfate, and sulfone [9]; and the internal components of oral care products such as toothpaste, mouthwash, tooth powder, etc., usually involve sodium dodecyl sulfate, sodium lauryl ether sulfate, etc. [9]. At the same time, various food and kitchen seasonings also contain food additives such as sodium, potassium, calcium, and ammonium sulfates [10]. These detergents and food additives mix with tap water through various water use behaviors to form sewage and affect the relative abundance of sulfur stable isotopes and sulfate concentration in tap water [11].

Therefore, this article aims to analyze the variation law of sulfur stable isotopes in sewage at the end of drainage area under different daily water use behaviors, and verify its reliability and stability in pipeline diagnosis