Explore the importance of biodegradable lubricants for sustainability and performance, how to test lubricant biodegradability, and how Aropha can help streamline the process for quicker, cheaper and more reliable results.

Why Biodegradability in Lubricants is Crucial

Lubricants, which are commonly used in machinery, engines and even marine vessels, are coming under scrutiny for their potential harm to ecosystems. When lubricants enter waterways or soil, they can disrupt aquatic life, harm biodiversity, and contribute to long-lasting pollution if they don’t break down properly.

In response to these concerns, many governments have enacted strict regulations to ensure that lubricants meet specific biodegradability criteria. These regulations, such as those from the U.S. Environmental Protection Agency (EPA) and OSPAR, aim to minimize the ecological footprint of lubricants and encourage the use of biodegradable lubricants environmentally acceptable lubricants (EALs). These lubricants are not only biodegradable but also non-toxic, reducing their potential for bioaccumulation in wildlife.

But biodegradability isn’t just about sustainability; it also plays a key role in the performance and longevity of lubricants. Products that break down more efficiently are often less harmful to systems and offer improved performance in environmentally sensitive applications, such as in marine or agriculture applications.

What are Biodegradable Lubricants? 

Biodegradable lubricants are called Environmentally Acceptable Lubricants, or EALs. Biodegradable lubricants, or EALs, are used to minimize the negative environmental consequences of lubricants. These lubricants meet specific standards in three key areas: biodegradation, toxicity, and bioaccumulation.

  • Biodegradability: EALs are designed to break down naturally and rapidly in the environment, reducing the duration and impact of any potential contamination.
  • Aquatic Toxicity: These lubricants exhibit minimal toxicity to aquatic organisms, ensuring that any accidental release poses a reduced risk to marine life.
  • Bioaccumulation: EALs are formulated to prevent accumulation in the tissues of organisms, thereby reducing the potential for harmful substances to concentrate up the food chain.

While all EALs are biodegradable, not all biodegradable lubricants qualify as EALs, as they must also meet the criteria for low aquatic toxicity and minimal bioaccumulation.

Ensuring biodegradability is often a critical first step in the development of EALs, but comprehensive testing is necessary to confirm compliance with all environmental standards.

Common Types of Biodegradable Lubricants

There are different types of biodegradable lubricants, each of which has different properties and applications:

  • Bio-Based or Vegetable Oils: These lubricants are derived from natural sources including plants and vegetable oils that are minimally modified. They are biodegradable, exhibit low toxicity, provide good performance, and do not thin at high temperatures.
  • Synthetic Esters: This biodegradable lubricant option is formulated via chemical synthesis of bio-based materials like animal fat or vegetable oils. They are made from synthetic esters that can be tailored to their specific intended applications. Synthetic esters are more common and have better benefits than some other EAL options. They perform well at various temperatures, have a high viscosity index, provide corrosion resistance, and meet biodegradability and toxicity requirements.
  • Polyalkylene Glycols: This type of biodegradable lubricant is comprised of synthetic lubricants made from petroleum-based materials. Despite that, they are highly biodegradable and water-soluble and exhibit the best low- and high-temperature viscosity of the EALs while providing corrosion resistance.

How to Determine Lubricant Biodegradability

To assess whether a lubricant meets biodegradability requirements, several standardized testing methods are used. These tests evaluate how quickly and effectively a lubricant breaks down in an aquatic environment, ensuring compliance with regulatory and environmental standards.

There are a few different testing methods that can be used to determine the biodegradability of your lubricants.

OECD301B: Ready Biodegradability Test

OECD 301B is one of the most widely used methods for determining the biodegradability of lubricants, base oils, and additives. As a “ready biodegradability test,” it measures how quickly a lubricant breaks down under aerobic conditions by monitoring CO₂ evolution. This test is often required for environmentally acceptable lubricants (EALs) and other biodegradable formulations. Since OECD 301B follows a similar format to ASTM D5864, results from either test can often be used to support regulatory submissions.

ASTM D5864

The ASTM D5864 tests for the biodegradability of lubricants by measuring CO2 evolution. This biodegradability test is done in continuously aerated bottles and within an aqueous aerobic environment.

During this test, activated sludge from municipal wastewater treatment plants is used as the inoculum. The test lubricant is placed in this sludge and the biodegradability of the lubricant is measured through the CO2 evolution that occurs during the course of the test. ASTM D5864 is designed for all lubricants that are non-volatile and non-inhibitory to the inoculum. If the test substance achieves high levels of biodegradation during this test, it may be assumed they are ultimately biodegradable in most aerobic aquatic environments.

ASTM D6731

The ASTM D6731 test is used to measure the biodegradability of lubricants by measuring oxygen consumption. Again, this test environment is aqueous aerobic, however, this test is done in closed respirometers, or closed bottles with headspace.

Much like the ASTM D5864 test, activated sludge from municipal wastewater treatment plants is used as the inoculum. The lubricant is added to the sludge within a closed respirometer and biodegradation is measured through the amount of oxygen that has been consumed over the course of the test.

This test is highly applicable with the ability to handle materials that are highly soluble, poorly soluble, insoluble, volatile, involatile, and/or absorbing. Again, if the test lubricant achieves high levels of biodegradation over the course of the test, it may be able to be deemed ultimately biodegradable in most aerobic aquatic environments.

Challenges in Lubricant Biodegradability Testing

While biodegradability testing is crucial for ensuring lubricants meet environmental standards, several factors make testing more complex than for other materials. Many lubricants, base oils, and additives exhibit properties that can interfere with standard test methods, making it difficult to obtain accurate and reliable results.

Factors That Complicate Biodegradability Testing

Certain physical and chemical characteristics of lubricants can hinder microbial breakdown or affect how biodegradability is measured. Some of the most common challenges include:

  • Poor Solubility: Many lubricant base oils and additives have low water solubility, limiting their availability to the microorganisms responsible for biodegradation. This is one of the most frequent issues in lubricant biodegradability testing.
  • Sorption: Some lubricants strongly bind to test vessel surfaces or organic matter, making them less accessible for biodegradation.
  • Volatility: Volatile components may evaporate before microbial degradation can occur, leading to underestimation of biodegradability.
  • Toxicity to Microorganisms: Some lubricant additives can be toxic to microbial cultures, inhibiting biodegradation rather than reflecting the material’s true environmental fate.
  • Ionization and Complexation: Some substances form chemical complexes or change properties depending on pH, impacting their biodegradation behavior in test conditions.
  • Instability and Chirality: Some lubricant components degrade or transform into different chemical structures over time, making it difficult to track their true biodegradation pathways.

Because of these challenges, not all standard OECD 301 tests are suitable for lubricant biodegradability assessment. Tests like OECD 301B (CO₂ Evolution Test) may not be ideal for substances with poor solubility or strong sorptive properties, as they could lead to artificially low biodegradation results.

Improving Bioavailability in Lubricant Biodegradability Testing

To overcome these challenges, Bioavailability Improvement Methods (BIMs) can be used to enhance the accessibility of poorly soluble or otherwise difficult-to-test lubricants. These methods increase the extent to which microorganisms can interact with the test substance, leading to more accurate biodegradation assessments. Common BIMs include:

  • Ultrasonic Dispersion: High-frequency sound waves break substances into finer particles, increasing surface area and dispersion in the test medium.
  • Use of Emulsifiers (Surfactants): Surfactants reduce surface tension, allowing hydrophobic substances to form stable emulsions and interact more effectively with microbes.
  • Adsorption onto Solid Supports: Some substances can be pre-adsorbed onto materials like silica gel to improve microbial access and prevent aggregation.
  • Dispersion with Oils: Certain inert oils, like silicone oil, can help distribute test substances more evenly in the test medium.

Applying the right BIMs is a specialized skill, and selecting the appropriate approach depends on the specific properties of the lubricant being tested. At Aropha, we leverage our expertise to optimize test conditions, ensuring that biodegradability results accurately reflect how a lubricant will behave in real-world environments.

How to Streamline Biodegradable Lubricant Development 

Biodegradability testing in lubricants can be complex and lengthy due to factors such as diverse formulations, environmental variability and regulatory inconsistencies. To overcome these challenges, it’s important to pick the right biodegradability testing partner.

Many companies looking for lubricant biodegradability testing turn to Aropha. We use the industry’s most advanced and cost-effective testing methods, combining customized AI models with lab testing to streamline biodegradable lubricant development.

Our ArophaAI biodegradability prediction software enables lubricant manufacturers to rapidly and accurately simulate biodegradation rates before undergoing more extensive testing. Plus, our wide range of lab tests are able to easily and quickly determine the biodegradability of lubricants so you can get them to market faster.

The result is streamlined biodegradable lubricant product development, reduced time to market and ensured compliance with evolving regulatory standards.

Ready to Test Your Biodegradable Lubricant? Contact Aropha to Get Started.

At Aropha, we combine cutting-edge automations and AI technology with traditional lab testing to provide faster, more reliable results and ensure that your lubricants meet all necessary biodegradability requirements.

Contact our team today to learn more about our biodegradability tests for lubricants.