- The effect was demonstrated using biodegradable mulch film placed in the field -
The National Agriculture and Food Research Organization (NARO) has demonstrated that an esterase-type enzyme accelerates the degradation of durable polyester biodegradable agricultural mulch films laid in the field. Mulch films are used in vegetable production. A day after the enzyme treatment, the strength of the film decreased, and became fragmented by tillage, with fewer large fragments. This method will make the use of biodegradable plastics easier in a variety of applications and reduce the amount of processed plastic products and their disposal.
Biodegradable plastics are polymeric compounds that break down into water and carbon dioxide. The use of mulch films to cover the surface of agricultural fields increases the yield of high-quality vegetables. When conventional nondegradable films are used, they have to be physically removed and disposed. The use of biodegradable plastic films has increased because they can be plowed into fields after cultivation and then decomposed by soil microorganisms, eliminating the need for after end-of-life treatment of the film. Recent biodegradable mulch films are designed to be durable so that they can be used in different environments to grow various vegetables. Durable products that resist breakage during the growing season are easier to use but decompose more slowly after use.
NARO is developing a method to accelerate the degradation of used biodegradable mulch films by treating them with biodegradable plastic-degrading enzymes. We discovered that the plant resident yeast, Pseudozyma antarctica, which lives in rice leaves and seeds, secretes a biodegradable plastic-degrading enzyme, named as PaE. We further discovered that PaE degraded poly(butylene succinate-co-adipate) (PBSA) and poly(butylene succinate) (PBS), which are components of early biodegradable mulch films, as well as amorphous polylactic acid. Recent biodegradable mulch films used in Japan contain poly(butylene adipate-co-terephthalate) (PBAT) as the main component, which degrades slowly, and in some cases polylactic acid (PLA), which biodegrades more slowly than PBAT. Notably, in this study, NARO revealed that PaE degraded PBAT. Films made of PBSA, PBS, and PBAT each immersed in PaE solution, were degraded from the surface of the film in the order PBSA>PBS>PBAT. They were thinned, and lost weight within a few hours. Furthermore, commercial biodegradable mulch films containing these biodegradable plastic materials lost weight when immersed in PaE solution.
Commercial biodegradable mulch films that were spread over ridges in the field lost strength a day after spraying PaE solution on their surface. Pieces of film that could be visually recovered from the field immediately after plowing had fewer large fragments and lower total weight than those without enzyme treatment. These results indicate that treatment with PaE promoted the degradation of biodegradable plastic films in the field.
In the future, this method should be investigated when combined with actual vegetable production. The number of types of biodegradable plastic products used outdoors, such as agricultural materials, will increase, leading to a greener society where used plastics will be degraded naturally and quickly.
Funding: This research was supported by the Research project commissioned by the Ministry of Agriculture, Forestry and Fisheries (MAFF): Science and Technology Research Promotion Program for Agriculture, Forestry, Fisheries and Food Industries, 25017A "Development of production technology and application technology for bioplastic agricultural material-degrading enzyme that contributes to labor saving in vegetable production", 25017AB "Advancement of manufacturing technology and application technology for biodegradable mulch film-degrading enzymes that contribute to labor saving in vegetable production", and "Research program on development of innovative technology JPJ007097" of the Bio-oriented Technology Research Advancement Institution (BRAIN), 01029C "Advancement of manufacturing technology and application technology for biodegradable mulch film-degrading enzymes that contribute to labor saving in vegetable production".
This research project is being applied for innovation creation enhancement research promotion project from "Biodegradable plastics and degrading enzyme research and development platform" organized by the Field for Knowledge Integration and Innovation® Industry-Academia-Government Collaboration Council, a mechanism for industry-academia collaborative research promoted by MAFF.
HP of Field for Knowledge Integration and Innovation (FKII)
Kitamoto H, Koitabashi M, Sameshima-Yamashita Y, Ueda H, Takeuchi A, Watanabe T, Sato S, Saika A, Fukuoka T(2023)Accelerated degradation of plastic products via yeast enzyme treatment. Scientific Reports. 13, 2386 https://doi.org/10.1038/s41598-023-29414-1