Critical thresholds in soil physical properties driven by microplastics

Growing evidence suggests that many ecological systems exhibit tipping points, thresholds at which small changes in stressors can trigger critical shifts in ecosystem properties. Whether such responses also occur in soils exposed to microplastics remains largely unexplored. Using a published dataset, we re-examined how microplastics affect soil physical properties, focusing on potential threshold concentrations at which those responses shift abruptly. We identified statistically supported threshold concentrations under which soil physical properties responded abruptly to microplastics incorporation by comparing linear, nonlinear, and piecewise models using Akaike Information Criterion (AIC). Unlike previous assumptions, our analysis of the investigated dataset indicated that abrupt effects can emerge at concentrations far lower than those typically used in classic dose-effect experiments, with threshold concentrations shifting depending on polymer type, particle shape, and ageing condition, and occurring at microplastic concentrations around 0.06%, 0.12%, 0.24% and 0.30% w/w. This study introduces a novel framework for detecting non-linear soil responses and identifying potential tipping points, suggesting that even low microplastic concentrations can alter soil physical properties. Given the dataset size and scope, these threshold estimates must be viewed as preliminary, pointing to candidate critical tipping concentrations rather than validated tipping points, and may depend on the chosen model representation. Future studies should incorporate fine low-dose gradients to confirm breakpoints, assess threshold types, and investigate soil compensatory processes and regime shifts in response to microplastic pollution.