Measuring a bio-based or biodegradable claim

Disputes over environmental claims are usually described as a question of intent. They are more often a question of metrology: two parties using the same word while measuring different quantities, or measuring nothing at all because no standard covers the condition being implied. It is worth setting out what can and cannot be determined.

Bio-based content is a radiocarbon measurement

Carbon of biological origin carries carbon-14, produced continuously in the atmosphere and taken up by living things. Fossil carbon has been buried far beyond the isotope’s roughly 5,700-year half-life and contains none that is measurable. A polymer’s bio-based carbon content is therefore an isotope ratio, determined against a modern reference under ASTM D6866 or its European equivalent, and it is one of the few environmental claims that can be settled analytically on a sample of the product itself.

Two limits matter. The measurement counts carbon atoms, so a bio-based carbon fraction is not the same number as a bio-based mass fraction once oxygen, nitrogen and mineral fillers are present, and the two are easy to conflate. More importantly, radiocarbon cannot verify a mass-balance claim. Where renewable feedstock is fed into a shared cracker and allocated to specific output by chain-of-custody bookkeeping, the molecules delivered are physically ordinary fossil molecules; the claim is an accounting one, and testing the product will report it as fossil. That is not a defect in either the claim or the test — it is a statement about which questions the test can answer.

Biodegradation is a claim about a condition, not a material

No material is simply biodegradable; a material biodegrades at a rate under a specified condition. The standards say so explicitly. EN 13432, and ASTM D6400 in the United States, define compostability for industrial conditions: at least 90 % conversion to carbon dioxide within six months in a controlled composting test held near 58 °C, disintegration to below 2 mm within twelve weeks, limits on heavy metals, and no adverse effect on plant growth in the resulting compost. EN 17033 sets a different bar for mulch films that stay in the field: biodegradation in soil at ambient temperature, over a period measured in years rather than months.

The distance between those two conditions is where most contested claims live. A polymer that comfortably passes an industrial composting test may be effectively inert in cool soil, fresh water or seawater, because its hydrolysis rate is strongly temperature-dependent and the industrial test sits above its glass transition. Home composting, landfill and open-environment littering are all conditions for which the widely cited certifications were never written.

The two axes are independent

The most common conflation is the simplest. Bio-based describes where the carbon came from; biodegradable describes what happens at end of life; neither implies the other. Bio-based polyethylene from sugarcane ethanol is fully renewable and does not degrade. Several compostable polyesters are made from fossil feedstock. A claim is verifiable only when it names which axis it is on, and under what condition — which is the substance behind recent regulatory moves against generic environmental wording, including the EU’s Directive (EU) 2024/825.