The science behind the number.
Why we use Arrhenius kinetics to measure biodegradation.
The problem with how biodegradation is tested.
Most biodegradation tests run at a single temperature in synthetic media. But a Midwest river runs about 10°C in spring. The Southern California coast sits around 16°C. A tropical lagoon reaches 28°C. A plastic doesn’t biodegrade at the same rate in all three environments, because temperature and microbial populations differ. The rate depends on which microbes are present.
A single-temperature test can’t tell you that. We test at multiple temperatures and use the Arrhenius equation to interpolate the rate at the specific temperatures your plastic will face.
What is the Arrhenius equation?
Almost every chemical reaction speeds up when you heat it and slows down when you cool it. The Arrhenius equation describes that relationship mathematically. It was published in 1889 and, with the right adaptation, it works for biodegradation the same way it works for any reaction: measure the rate at a few temperatures, plot the curve, read off any temperature you need.
How Arrhenius works for biodegradation.
Arrhenius kinetics captures how that rate changes with temperature, so a few measured points become a predictable curve.
We measure biodegradation rates at multiple temperatures. The Arrhenius equation connects those measured rates into a single curve. From that curve, we can read the rate at any temperature within the range we tested.
The result: a defensible lifetime estimate for your plastic across the temperatures it will face. Not a guess. A number with a measured margin of error.
The rate at any temperature inside that range is read off it.
We never extrapolate outside the temperatures we actually tested.
Every lifetime estimate is interpolated within the measured range.
Why this matters for your product.
A single-temperature test tells you your plastic biodegrades. Arrhenius kinetics tells you how fast, at what temperature, and how long it is expected to persist. That’s the difference between a marketing claim and a defensible number.
KinetiKs developed the Arrhenius kinetic methodology behind ASTM International D8646, Standard Test Method for Calculating and Reporting the Estimated Biodegradation Time of Non-Persistent Plastics Designed for Use in Aquatic Environments, and applies it to every test we run.
Ready to test?
Our testing follows ASTM D8646.
For technical details, the full method is defined in ASTM D8646, available from astm.org.
Results reflect laboratory conditions and standard test methods. Actual environmental degradation may vary.