Comparative Soil Burial and Microbial Degradation of Starch-Based Bioplastics

Abstract

Starch-based films are renewable materials with potential for short-lived packaging and agricultural applications, but soil-burial mass loss depends on formulation, film geometry, plasticizer leaching, soil properties, environmental conditions, and microbial activity. To compare the four-week soil-burial mass-loss proxy of locally extracted wheat- and rice-starch films prepared under the reported nominal formulation, and to describe presumptive culturable bacterial morphotypes recovered from the surrounding soil. Films were prepared from 2 gram (g) starch, 100 mL distilled water, 5 mL glycerol, and 2 mL vinegar or acetic acid, then buried approximately 5 centimeter (cm) deep in garden topsoil for four weeks. The source record reported three samples per starch type, but did not document whether they were independent biological batches or technical subsamples. Endpoint mass-loss percentages were reconstructed from the displayed replicate masses. Welch and exact permutation tests were calculated, with the exact permutation test designated as the primary inference because n = 3 per group. Wheat films showed a mean endpoint mass-loss proxy of 75.98 % (SD = 2.09 %) and rice films 50.95 % (SD = 8.61 %), a mean difference of 25.02 percentage points. The reconstructed Welch test gave t (2.24) = 4.89, p = 0.031, whereas the exact two-sided permutation test gave p = .10. Wheat films showed greater endpoint mass loss under the reported preparation and burial conditions, but the experiment does not isolate starch source as the causal determinant.