Surfactant-mediated effects on hydrological and physical soil properties: a data synthesis

Soils are under threat of a multitude of anthropogenic factors affecting the complex interplay of various physical and hydrological soil processes and properties. One such factor is the group of surface-active compounds. Surfactants have a broad range of applications, and can reduce solid-liquid interfacial forces and increase wettability and dispersion of particles. Surfactant effects are context-dependent, giving rise to a wide range of reported effects on different soil processes and properties. Here, we evaluate the evidence base of surfactant research on 11 hydrological and physical soil variables. Our goal was to identify knowledge gaps and to test the robustness of proposed surfactant effects. We found that the current knowledge base is insufficient to reach strong data-backed conclusions about effects of surfactants in soils. We identified a unique case of bias in the data as a result of conflated patterns of lab and field studies. We could not support the hypothesis that surfactant charge determines soil effects for any of the tested soil variables. We believe that further experiments on surfactant mediated effects on soil properties and processes are urgently required, paying attention in particular to improving experimental design and data reporting standards. Graphical abstract