Bioplastics in agricultural soils: Biodegradability, analytical techniques, and soil microbial impact

The use of bioplastics is promoted as an alternative to mitigate plastic pollution in agricultural soils. However, their environmental safety remains insufficiently controlled under realistic agricultural conditions. This review critically examines the behavior of bioplastics in agrarian soils by integrating evidence on degradation mechanisms, analytical methodologies, and soil-plant biological responses. Based on a bibliometric analysis and an in-depth study of experimental evidence, we emphasize that commonly applied techniques often capture surface alterations or material disintegration, providing a limited view of the fate of polymer-derived carbon. This methodological bias may lead to overestimating biodegradation rates and environmental safety. Consequently, biodegradable microplastics and other intermediate residues could persist in soils, particularly under repeated seasonal applications. Biological interactions with bioplastics are highly context-dependent and do not necessarily indicate functional integration into soil biogeochemical cycles. Short-term biological responses may show adaptation or physical effects rather than long-term environmental benefits. To address these limitations, we propose an integrative conceptual framework that links degradation pathways, analytical tests, and biological responses, emphasizing that these concepts must be evaluated jointly to enable robust environmental risk assessments. We identify critical knowledge gaps, including insufficient reporting of key experimental parameters, such as temperature, moisture, or material thickness, the lack of data on the final fate of carbon, and limited long-term studies. Overall, this work underscores that biodegradability alone does not ensure environmental safety and highlights the need for risk-oriented and context-aware assessments under realistic agricultural conditions to guide the responsible use of bioplastics in agricultural soils.