"Biodegradable" is one of the least disciplined words in chemistry marketing. Almost everything degrades eventually. The question a regulator, a retailer or a formulation lead actually asks is narrower: does this substance reach a defined degradation threshold inside a defined window under a defined test? That question has a standard answer, and it is called the OECD 301 series.
- Series
- OECD 301A to 301F
- Pass criterion
- 60 % ThOD or 70 % DOC removal in 28 days
- 10-day window
- Threshold must be met within 10 days of reaching 10 %
- PureSurf result
- Readily biodegradable, OECD 301F (GLP)
Ready, inherent and ultimate biodegradation
Ready biodegradability is the strict category. It uses a small inoculum, no adaptation period and a short test window, so passing implies the substance will degrade rapidly in most environments. Inherent biodegradability is a weaker statement: it shows a substance can degrade under favourable conditions, not that it will do so quickly in a real receiving water.
Ultimate biodegradation means full mineralisation to carbon dioxide, water and mineral salts, with no persistent fragment left behind. Primary biodegradation, by contrast, only means the parent molecule lost its surface-active structure, which is a much lower bar.
The six OECD 301 tests
All six measure ready biodegradability, but they differ in what they track and which substances they suit. Poorly soluble or volatile materials rule out some methods, which is why the chosen test matters when comparing two data sets.
| OECD 301A | DOC Die-Away. Tracks dissolved organic carbon removal. |
|---|---|
| OECD 301B | CO2 Evolution (Modified Sturm). Tracks carbon dioxide produced. |
| OECD 301C | Modified MITI (I). Tracks oxygen uptake in a closed respirometer. |
| OECD 301D | Closed Bottle. Tracks dissolved oxygen depletion, suits low-solubility substances. |
| OECD 301E | Modified OECD Screening. DOC-based, low inoculum. |
| OECD 301F | Manometric Respirometry. Tracks oxygen demand, widely used for surfactants. |
How to read a pass
A substance is readily biodegradable when it reaches 60 % of theoretical oxygen demand or carbon dioxide evolution, or 70 % dissolved organic carbon removal, within 28 days. Crucially, the threshold must be met within a 10-day window that starts once degradation passes 10 %.
That 10-day window is where many marketing claims quietly fail. A substance reaching 65 % on day 27 after a slow start has not passed the ready criterion, even though the headline number looks convincing.
Where PureSurf chemistry sits
NEXOVANT is readily biodegradable under OECD 301F, tested to GLP rather than screened internally. The same GLP programme confirmed that the material is non-mutagenic (OECD 471) and not corrosive to skin (OECD 431), and characterised aquatic toxicity under ISO 11348-3:2007.
Biodegradability and toxicity are separate questions and both matter. A molecule can degrade quickly and still be acutely toxic on the way. NEXOVANT F Pro shows 14× lower and NEXOVANT F Eco 57× lower aquatic toxicity than conventional amine oxide benchmarks, with up to 96 % lower algal toxicity.
Frequently asked questions
Does bio-based automatically mean biodegradable?
No. Bio-based refers to the carbon source, biodegradability to end-of-life behaviour. Some fossil-derived molecules degrade readily and some bio-based ones do not. Only a test result settles it.
Why is OECD 301F common for surfactants?
Manometric respirometry handles the concentration range and solubility behaviour of surfactants well and gives a continuous oxygen demand curve, which makes the 10-day window easy to verify.
Is NEXOVANT readily biodegradable?
Yes. NEXOVANT is readily biodegradable under OECD 301F, tested under GLP conditions.
