The topic of “biodegradability” has become extremely important over recent years, but still may not be fully understood. The following is a basic overview for formulators and anyone wishing to know more about this critical issue. (Note that regulations, definitions, and practical guidelines on biodegradability are continually changing, and the comments in this blog are intended to offer general insights, not legal definitions or advice.)
Simply put, biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi, and once broken down, the byproducts are carbon dioxide and water vapor. “Bio” is the key prefix here; the difference between “degradable” and “biodegradable” is that while “degradable” products can be broken down by chemical or biological processes, “biodegradable” materials can only be broken down by biological processes.
The concern for biodegradable products began with the issue of microplastics, first detected in the 1970s in the ocean as plastic residue, but not termed “microplastics” until the mid-2000s. (A good and comprehensive article on this by Napper and Thompson was published online in 2020.) Many multinational companies have stopped using microplastics (microbeads) in their formulations and other brands are following, but let’s clearly define what are, and are NOT, microplastics! To qualify as a microplastic, four criteria must be met:
- It must be a polymer
- It must be solid (at RT)
- It must be in particulate form
- It must be under 5mm in size
All four criteria must be met – if even a single one of these four is not present, the substance is NOT considered a microplastic. And to complicate matters further, there are many exclusions even if these four criteria are met, including the following:
- The material is natural
- The material is degradable
- Its solubility is > 2 g/liter
- No carbon atoms in its chemical structure
- Its release to the environment is prevented when used
- Its physical properties are permanently modified during end use
- It is permanently incorporated into a solid matrix during end use
- And likely more…
Just because your products may be “natural” does not mean they are “biodegradable” – measurement is key! As mentioned by Dr. Martin Perry, Advanced Development Safety Laboratories, at SCS Formulate in 2021: “Although natural content is good to know, and there is a perception that natural ingredients are more biodegradable than synthetic ones, knowing the biodegradability is important. The natural content of your product or your organic content is not going to be sufficient for you to substantiate anything on biodegradability.”
To be precise, most companies adhere to the standard of “readily biodegradable”, defined as the ability of a product to biodegrade quickly and completely (≥ 60% by OECD 301A-F/ASTM D7373 testing) within 28 days. You might also hear the term “inherently biodegradable,” defined as between 20% and 60% biodegradability as measured by OECD 301A-F testing, but “readily biodegradable” is stricter and preferable.
From the OECD iLibrary: “The OECD Guidelines for the Testing of Chemicals is a collection of about 150 of the most relevant internationally agreed testing methods used by government, industry and independent laboratories to identify and characterize potential hazards of chemicals. They are a set of tools for professionals, used primarily in regulatory safety testing and subsequent chemical and chemical product notification, chemical registration and in chemical evaluation. They can also be used for the selection and ranking of candidate chemicals during the development of new chemicals and products and in toxicology research. This group of tests covers environmental fate and behaviour. In 2017, the section 3 “Degradation and Accumulation” was renamed to “Environmental fate and behaviour” to take into account Test Guidelines measuring endpoints such as dispersion, aggregation.”
As a final note, microplastics and biodegradability concerns are part of a larger issue of minimizing environmental pollution. Some may equate this trend with the apparent discovery of reef damage caused by certain organic sun filters, specifically octinoxate and oxybenzone. There are bans in place on octinoxate and oxybenzone in many countries, including the US (Hawaii, Florida, US Virgin Islands), Aruba, Bonaire (off the coast of Venezuela), Palau and parts of Mexico. However, this is not a biodegradability issue as much as it is a toxicity issue, and the science is still unclear as to the actual effect of residual organic sunscreens on coral reefs.
Ben Blinder is the Executive Director, Business Operations at Gattefossé USA, with P/L responsibility for the personal care and pharmaceutical business units in the US and Mexico. He is also a founding member of the Advisory Committee on Diversity & Inclusion for Gattefossé in North America. Ben holds a BS in chemical engineering from Lehigh University.