What is meant by the term "bio-oil"?

You reported on synthetic hydraulic oils that have proven themselves in long-term use in construction machinery in your customer magazine ÖlChecker. Specifically, this involved HEPR oils. These PAO (polyalphaolefins)-based fluids meet CECL- 33-A-93, which you say is associated with hydraulic fluids that are more rapidly biodegradable. However, is this guideline even considered today as a method for classifying synthetic oils as "more rapidly biodegradable hydraulic fluids"?

OELCHECK answers:

With the article "Geiger builds with earth, stones, gravel and moves Liebherr construction machinery with synthetic oils", our main aim was to convey that synthetic base oils allow a hydraulic oil to be used for a significantly longer period of time. However, we only addressed the topic of "organic oil" in passing. At the time when these oils were filled in about 10 years ago, the term "organic oil" was not as clearly defined as it is today. Oils according to the CEC test were considered organic.

However, in order to rule out any misunderstandings, we would like to comment explicitly on this once again here.

Caution is always necessary when using the attribute "bio-oil", which is usually used to describe the "faster biodegradability" of a hydraulic fluid compared to mineral oil. In principle, it must be questioned which test method was used to substantiate this claim. Even today, some lubricant manufacturers advertise with the passed test according to CEC-L-33-A-93 (DIN 51828-2) in their partly outdated data sheets. But in reality, this test, which was once developed for classifying oils for two-stroke outboard engines, has long since become obsolete for hydraulic oils and is no longer a benchmark.

The user expects a "rapidly biodegradable hydraulic fluid" or - in colloquial terms - "bio-oil" to be significantly less harmful to the environment than a conventional product and thus to have a significantly lower risk potential in terms of contamination of water and soil in the event of an accident.

Today, ISO 15380 is the internationally valid standard for the classification of rapidly biodegradable hydraulic oils into the respective substance groups. It also defines HEPR hydraulic fluids (Hydraulic Oil Environmental Polyalphaolefins and Related Products). For HEPR fluids, ISO 15380 requires, among other things, a passed test of complete biodegradability according to OECD 301 guidelines or equivalent standards. CEC-L-33-A-93 or other CEC methods for determining primary biodegradability are clearly not among them. The OECD 301-B test procedure for the rapid biodegradability (>60%) of hydraulic oils is now an international standard and is also anchored in ISO 15380. When awarding the well-known eco-labels such as the EU Flower (R1, T3) and the Blue Angel (RAL-ZU 79, since 2007), the test according to OECD 301-B, among others, is a prerequisite.

If a lubricant manufacturer states that its HEPR oil can be called "bio-oil" because it meets the conditions cited in ISO 15380, then the oil must also be tested for biodegradability according to OECD 301-B. Rapid biodegradability, which must be above 60% in these tests, is required. Many HEPR oils that meet ISO 15380 are typically a blend of PAO and ester-based base oils.

Our advice: When the label "bio-oil" is used, look for compliance with the biodegradability specified in ISO 15380 or for the eco-labels on the containers. These may only be used in advertising if proof of faster biodegradability is provided. Also always pay attention to the respective valid national environmental laws and requirements of the responsible authorities!

Read also: Organic oils & trend analyses