Comparative degradation and microbial impact of biodegradable bags in managed and unmanaged soils in Croatia

The breakdown of biodegradable plastics in natural environments varies widely and is influenced by both the polymer's properties and environmental factors. The aim of this study was to compare the degradation of three types of biodegradable bags commercially available in Croatia in managed (tilled fertilized soil with application of herbicides) and unmanaged soil (no mechanical or chemical treatment) from the same geoenvironment. Bags were exposed in both soil management types and collected after 3 and 6 weeks to compare changes in mechanical properties (surface structure and sample damage, tensile breaking force and breaking elongation, mass per unit area) over time and between soil types. Additionally, at the 6-week sampling point, we collected soil samples from the surface of each exposed bag and from the surrounding soil to analyze changes in microbial diversity and abundance. The results have shown that: (i) all three bag types degraded in both soil types in a time-dependent manner; (ii) soil management type was a strong determinant of the composition of soil microbial communities and also affected the degradation rate of bioplastic bags; (iii) the presence of bioplastics bags resulted in reduction of soil microbial diversity and changed the relative abundance of some bacterial taxa. The study adds to the knowledge of the fate of bioplastics in agricultural and natural (unmanaged) soil, urgently needed to better predict the risks accompanied with the ever-increasing usage of such products.