Pathogenic bacteria can be discharged in the environment through natural as well as anthropogenic activities. Once in the environment, they may contaminate soil and sediments and migrate towards water bodies. Transient chemical conditions may occur in soil/sediments and favor mobilization of bacteria, e.g., upon the reduction of salinity (or ionic strength). However, the magnitude of this phenomenon and its relationship with particle size is not well understood, yet.

In this work, we investigated the transport of Escherichia coli under variable salinity conditions (between 1 and 20 part per thousand, ppt) and for different soil grain sizes (between 150 and 710 μm). A model developed in our group was applied in this work. It couples bacteria and salinity transport equations in order to account for transient water composition in the description of bacteria migration. The model was calibrated and validated with laboratory experiments. The tests were monitored continuously with UV–Vis spectroscopy, which allowed to record highly resolved concentration fronts. The results show that salinity increases the retardation of the bacteria. Upon salinity drop, a release of bacteria occurs forming a peak whose magnitude increases with salinity change. This effect becomes more important as the grain size decreases. Simulations suggest that the dominant retention mechanism is attachment for coarse sand and straining for fine sand. The retention can be reversed as the salinity is reduced causing a sudden bacteria mobilization. Such a behaviour may have important implications on microbial contamination of water bodies when soil/sediments undergo transient chemical conditions.

病原菌可通过自然和人为活动排放到环境中。一旦进入环境，它们可能会污染土壤和沉积物并迁移到水体中。瞬时化学条件可能出现在土壤/沉积物中并有利于细菌的活动，例如在盐度（或离子强度）降低时。然而，这种现象的严重程度及其与粒径的关系尚不清楚。

在这项工作中，我们研究了在不同盐度条件下（1 到 20 份，ppt）和不同土壤粒度（150 到 710微米）下大肠杆菌的运输。我们小组开发的一个模型应用于这项工作。它将细菌和盐度传输方程耦合起来，以便在描述细菌迁移时考虑瞬时水成分。该模型通过实验室实验进行了校准和验证。使用 UV-Vis 光谱连续监测测试，这允许记录高度分辨的浓度前沿。结果表明，盐度增加了细菌的延迟。在盐度下降时，细菌的释放会形成一个峰值，其幅度随着盐度的变化而增加。随着晶粒尺寸的减小，这种影响变得更加重要。模拟表明，主要的滞留机制是粗砂的附着和细砂的过滤。当盐度降低导致细菌突然动员时，保留可以逆转。当土壤/沉积物经历瞬态化学条件时，这种行为可能对水体的微生物污染产生重要影响。