Certified soil-biodegradable mulch films do fully biodegrade in soil. This can be proven by testing and referring to the standard EN 170339 (9) (or ISO 23517) (10), which specifies the requirements and test methods for biodegradable mulch films used in agriculture and horticulture. Products complying with that standard can get certification by DIN CERTCO. The label OK biodegradable SOIL is certified by TÜV AUSTRIA, Belgium, in case a product meets the requirement of their certification scheme.
For both certifications, the mulch film material must biodegrade in laboratory experiments, with a minimum of 90% conversion (absolute or relative to a positive control) of the carbon from the material into CO2 in no longer than 2 years at room temperature. This guarantees that soil microorganisms will be able to biodegrade the material in the soil and that no persistent microplastic will be left after disintegration.(11) Actual rates of biodegradation under real life field conditions will depend on several factors, such as material composition and thickness of the film. These parameters are usually used to adjust the properties according to the needs of the crop. In addition, water availability, soil composition, nutrients, and oxygen availability, as well as other climate and agricultural parameters, will influence the behaviour under real life conditions. This applies to certified soil-biodegradable mulch films just as much as to every other natural material. It is to be noted that, while very fast biodegrading materials might be seen as desirable from an end-of-life perspective, too fast biodegradation will make these materials unsuitable for the intended function, e.g. because of premature biodegradation before plant growth.
(9) EN 17033: Plastics – Biodegradable mulch films for use in agriculture and horticulture – Requirements and test methods.
(10) ISO 23517:2021: Plastics — Soil biodegradable materials for mulch films for use in agriculture and horticulture — Requirements and test methods regarding biodegradation, ecotoxicity and control of constituents.
(11) See: Maurizio Tosin et al., Disintegration and mineralization of mulch films and leaf litter in soil, Polymer Degradation and Stability, Volume 179, 2020