Biodegradability standardization and testing (ISO 17088, EN 13432)

A standard such as EN 13432 or ISO 17088 does not certify that a material is biodegradable in the abstract. It fixes an experiment and asks what fraction of the material’s carbon leaves the system as CO2 within a stated time. The certificate therefore attaches to the pair of material and environment, never to the material alone, and the rest of the testing battery exists to keep that one number honest.

What the instrument measures

The core method is respirometry. Test material is mixed into an inoculum — mature compost, soil, or seawater with its microbial community — in closed, aerated vessels held at a defined temperature. Either the carbon dioxide evolved is trapped and quantified, or the oxygen consumed is measured. Blank vessels with inoculum but no material run in parallel, because the inoculum itself respires, and their gas exchange is subtracted. The denominator is the theoretical amount of carbon dioxide the material would release on complete oxidation, calculated from its measured carbon content. The reported result is the quotient of net CO2 evolution by this theoretical value: a mineralisation percentage. What has been measured is a gas flux integrated over months — not “decomposition” in the everyday sense of visibly falling apart.

Why the result belongs to the conditions

Temperature, moisture, nutrient supply and the composition of the microbial community set both the rate and the extent of mineralisation. A polymer that clears the pass fraction in managed, hot compost may stall in ambient soil; the marine test is the hardest of the three because the inoculum is dilute and the conditions least reproducible. This is why a claim must carry its environment with it. Home composting, which lacks a thermophilic phase, is a separate and harder regime with its own requirement of full biodegradation within 180 days. The same molecule in three environments is three different experiments, not one quantity with correction factors.

Fragmentation is not mineralisation

Disintegration is tested separately, as a physical sieving test: a material can break into pieces while all of its carbon stays put. Mineralisation is the chemical endpoint. Alongside it sit ecotoxicity tests — whether the resulting compost supports plant germination — and limits on heavy metals and fluorine, which protect the compost, not just the polymer’s fate. One arithmetic trap remains: mineralisation is not linear in composition. A slow component, even a minor one, leaves a persistent residue that a bulk curve hides, and the 2026 revision of the Seedling scheme — demanding ultimate-biodegradability evidence for each organic constituent in the one-to-fifteen-percent range — is precisely a recognition of that arithmetic.

Where the method is thin

The inoculum is a biological reagent with batch-to-batch variability; the tests run for months; and the standardised conditions were chosen for comparability between laboratories, not for predicting any particular composting facility — which is why field testing is offered as a complement, never a substitute. Extrapolating from the vessel to the windrow is a judgement call. Note also the boundary of the whole exercise: biodegradation in soil says nothing about the state of the soil itself. That is a different measurement, covered in soil health assessment.