Q: What makes a lubricant Environmentally Friendly?
There are many definitions of environmentally friendly. For instance, a lubricant can be environmentally friendly if it doesn’t pollute the environment which can either be understood as low toxicity or a reduced number of times that the oil is disposed.
However, there are three main factors which are considered when deeming a lubricant environmentally friendly2;
- Speed at which the lubricant biodegrades if introduced into nature
- Toxicity characteristics that may affect bacteria or aquatic life
- Bioaccumulation potential
Biodegradability is defined as the measure of the breakdown of a chemical or chemical mixture by micro-organisms. It is considered at two levels namely;
- Primary biodegradation - loss of one or more active groups renders the molecule inactive with respect to a particular function
- Ultimate degradation – complete breakdown to carbon dioxide, water and mineral salts (known as mineralisation)3
Biodegradability is also defined by two other operational characteristics known as:
- Ready Biodegradability – occurs where the compound must achieve a pass level on one of the five named tests either, OECD, Strum, AFNOR, MITI or Closed Bottle3
- Inherent Biodegradability – occurs when the compound shows evidence in any biodegradability test.3
The toxicity of a lubricant is measured by the concentration of the test material required to kill 50% of the aquatic specimens after 96 hours of exposure (also called the LC50)1
The term bioaccumulation refers to the build-up of chemicals within the tissues of an organism over time. Compounds can accumulate to such levels that they lead to adverse biological effects on the organism. Bioaccumulation is directly related to water solubility in that the accumulations can be easily soluble in water and not move into the fatty tissues where they become lodged.
Common Base Oils
There are three of the most common base oils that are Environmentally Acceptable2:
- Vegetable Oils
- Synthetic Esters
- Polyalkylene Glycols (PAGs)
These all have low toxicities and when blended with additives or thickeners for the finished lubricant, they should be retested to ensure that the additives / thickeners have not compromised the environmentally acceptable limits.
Some lubricants can carry the “German Blue Angel Label” if all major components meet OECD ready biodegradability criteria and all minor components are inherently biodegradable.
Based on the requirements by Marpol, the International Maritime Organization (IMO) and current legislation from the European Inventory of Existing Commercial Chemical Substances (EINECS), a product may be considered acceptable if it meets the following requirements:
- Aquatic toxicity >1000ppm (50% min survival of rainbow trout)
- Ready biodegradability > 60% conversion of test material carbon to CO2 in 28 days, using unacclimated inoculum in the shake flask or ASTM D5846 test 1.
- Lubrication Fundamentals Second Edition, Revised and Expanded. D.M. Pirro (Exxon Mobil Corporation Fairfax, Virginia), A.A. Wessol (Lubricant Consultant Manassas, Virginia). 2001.
- United States Environmental Protection Agency Office of Wastewater Management Washington, DC 20460. Environmentally Acceptable Lubricants. https://www3.epa.gov/npdes/pubs/vgp_environmentally_acceptable_lubricants.pdf
- Chemistry and Technology of Lubricants 3rd Edition, Chapter 1, R.M. Mortier, M.F. Fox, S.T. Orszulik)