There is no single definition of biodegradability. Throughout the United States and internationally there is a wide range of environmentally preferable definitions. The ASTM 6064 has defined biodegradable as a function of degree of degradation, time, and test methodology. Figure 3 shows the different classifications of biodegradation.

Despite these definitions, there are two widely used designations for biodegradability, readily and inherently. Readily biodegradable is defined as degrading 80% within 21 days as measured by the decrease of a test sample. This type of degradation is preferable because in most cases, the fluid will degrade long before environmental damage has occurred. Because of this, little is required in terms of long-term bio-remediation. Vegetable-based lubricants and some synthetic ester-based products exhibit ready biodegradation.

There are several petroleum-based lubricants that claim “inherent biodegradability.” Inherent biodegradation is defined as having the propensity to biodegrade, with no indication of timing or degree. These types of products can persist in the environment for years, continuing to cause substantial damage. They require long-term remediation due to the environmental persistence. Typically, these products are petroleum-based, like conventional lubricants. Figure 4 illustrates the difference in degradation timing of a readily biodegradable product compared to an inherently biodegradable product.

This graph easily shows the difference between a readily biodegradable product and an inherently biodegradable one. The EPA and Coast Guard use this differentiation when evaluating an oil release.

Eco-toxicity is critical to living organisms

Another measurement to determine environmental effect of a lubricant is “eco-toxicity.” Historically, tests for eco-toxicity have concentrated on the aquatic environment with a number of standard test procedures. Most typically, the tests are for “acute toxicity.” This is a measurement of the concentration required to kill various organisms over a short period of time ranging from 24-96 hours. Depending on the tests and its end points, the toxicity of a fluid is described by a loading rate that has a 50% effect (EL50) or causes 50% mortality (LL50) after the stated time. That is, at what concentration of fluid one half of the sample organisms die. Figure 5 shows the different classifications of ecotoxicity.

Performance of bio-fluids

There is a wide variety of performance levels among biodegradable products. When an environmentally preferable product is required outside the common temperatures range, a biodegradable synthetic is usually required. While offering biodegradation, these products can operate in temperatures in excess of 400° F and still offer long fluid life. As would be expected, these products are significantly more expensive.

Care must be taken in choosing the appropriate product for the specific application. Responsible Environmentally Preferable Product (EPP) suppliers can clearly indicate their definition of “environmentally preferable.” The Federal Trade Commission has been very specific in its requirements for environmental claims and state “look for claims that give some substance to the claim, the additional information that explains why the product is environmentally friendly.” Many “would-be” EPP suppliers use misleading environmental claims such as “inherently biodegradable” or “food-grade.” Suppliers should be able to support performance claims with testing data. These data can include standard industry tests (ASTM), field-testing, and equipment manufacturer tests. Unless an EPP supplier specializes in environmentally preferable products, they are probably not an expert in the field.