FDA-hydrolysis activity: A pre-screening tool for optimizing compost selection in standardized plastic biodegradation testing

Current ISO 14855–1 standards for assessing plastic biodegradability under composting conditions rely on physicochemical parameters, such as pH and volatile solids, to select compost inocula. However, these indicators do not directly reflect microbial activity, which is central to biodegradation processes. This study proposes fluorescein diacetate hydrolase (FDA-H) activity as a rapid, integrative biological indicator to pre-screen composts before standardized biodegradation testing. FDA-H activity was measured in five composts and showed a strong correlation with early CO₂ evolution (r = 0.93), reflecting initial microbial metabolic potential. Moderate correlations were also observed with final biodegradation rates of cellulose and polybutylene succinate (PBS), suggesting that microbial community shifts and substrate-specific adaptation influence long-term outcomes. Metagenomic analysis supported this by revealing distinct microbial succession patterns during degradation, especially for synthetic polymers. We also compared FDA-H with standardized microbial activity assays, including respiration and dehydrogenase activity. Unlike these methods, FDA-H captures extracellular hydrolytic enzyme activity relevant to polymer breakdown and offers advantages in speed and operational simplicity. While FDA-H does not replace ISO/OECD biodegradation standards, it complements them by providing early-stage insight into compost suitability. Integrating FDA-H into existing testing frameworks could enhance the reliability, efficiency, and biological relevance of compost selection, ultimately improving standardized biodegradation assessments.