Incorporation of Natural Biostimulants in Biodegradable Mulch Films for Agricultural Applications: Ecotoxicological Evaluation

This study deals with the incorporation of biostimulants of natural origin in a biodegradable polymeric matrix, with the aim of developing mulch films that, when degraded in the soil, release bioactive compounds that improve soil quality and favor the agronomic growth of crops. Three types of commercial biostimulants were used: one based on seaweed extract, one on lignosulfonates, and one on plant-derived essential amino acids. To ensure the thermal stability of the biostimulant compounds during processing, thermogravimetric analyses (TGAs) were carried out, and a methodology based on the adsorption of the biostimulants onto porous substrates was developed, enabling their effective incorporation into the polymeric matrix. The formulations obtained have been processed by blown film extrusion at a pilot scale. In addition, the presence of film residues in soil was analyzed by pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS). The results indicate that the proposed methodology supports the integrity of the biostimulants in the films obtained. After the incubation period studied, complete degradation of the biopolymer and the absence of film residues in the soil were confirmed. Furthermore, it was confirmed that this final product had no adverse effects on organisms that were representative of the two end-of-life scenarios, with the exception of the film functionalized with the commercial biostimulant based on seaweed extract, which showed a negative effect on terrestrial higher plants.