a)  What is Biodegradability?

 
b)  If Biodegradable, how biodegradable is the material?

Claims like "Environmentally Acceptable", "Environmentally Friendly", "Environmentally Preferable", and "Environmentally Responsible" are also used to describe a material that was produced by biodegradable materials or, in most cases, part biodegradable material without knowing if the whole formulation could be rated as biodegradable. In many cases, when the word "Biodegradability" is used, it meant that the lubricant product is more biodegradable than petroleum base oils or formulas.

A Biodegradable classification was needed for a very complex system, and the industry recognized the following tests to determine biodegradability of lubricants:

• OECD 301B Modified Sturm
• ASTM D-5864
• CEC L-33-T-82

These tests are discussed in section 6.3  Standardized Biodegradability Tests, presented below.

 
Biodegradability

Biodegradability is not only a property or characteristic of a substance, but is also a system's concept, i.e. a system with its conditions determines whether a substance within it is biodegraded. When material is released into the environment, its fate depends upon a whole range of physiochemical processes and its interaction with living organisms. The most stable compound of carbon is Carbon Dioxide. All the more reduced organic compounds are thermodynamically unstable and will be randomly attacked by microbial enzymes, provided that they have some structural similarity to naturally occurring substrates.

The California Advertising Statute, amended on April 30, 1991, states that a manufacturer cannot claim that a product is biodegradable unless it meets the following definition:

The Degradation/Accumulation Expert Group of the OECD Environment Committee has established a series of tests which classify compounds as:

The EPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS 835.3110) has developed this guideline through a process of harmonization which has blended the existing testing guidance and requirements published by the following agencies:

• Office of Pollution Prevention and Toxics (OPPT)
   
• Title 40, Chapter I, Subchapter R of the code of Federal Regulations (CFR)
   
• Office of Pesticide Programs (OPP) which appeared in publications of the National Technical Information Service (NTIS)
   
• Organization for Economic Cooperation and Development (OECD)
   

Note: OECD's test is most recognized in the lubricant industry.

Listed in the EPA Guidelines is OECD 301-B CO2 Evaluation Test (Modified Sturm), "Biodegradability Assessment for Water Soluble and Insoluble Chemical Compounds and Formulations".

Inherently Biodegradable

Inherently Biodegradable is a classification of chemicals for which there is unequivocal evidence of biodegradation (primary or ultimate) in any test of biodegradability.

 
Ultimate Biodegradation

Ultimate Biodegradation (Aerobic) is the level of degradation achieved when the test compound is totally utilized, 100% biodegraded by microorganisms resulting in the production of carbon dioxide, water, mineral salts, and new microbial cellular constituents (biomass).

Note:  United Bio Lube's entire Biobased Lubricant product line is rated Ultimate Biodegradation, the highest U.S.D.A. rating attainable.

 
Readily Biodegradable

Readily Biodegradable is an arbitrary classification of chemicals which have passed certain specified screening tests for ultimate biodegradability; these tests are so stringent that it is assumed that such compounds will rapidly and completely biodegrade in aquatic environments under aerobic conditions.

 
Primary Biodegradation

Primary Biodegradation is the alteration in the chemical structure of a substance, brought about by biological action, resulting in the loss of a specific property of that substance.

(Published by EuroLabs Ltd. and referenced from Lubrizol's Biodegradability Review)

Eurospec makes distinctions between Readily and Inherently biodegradable.

Inherently biodegradable is used to describe organic compounds, which are not Readily biodegradable within the 28 days, but over prolonged exposure periods, with adapted organisms and lower concentrations of the chemical, will exhibit levels of degradation similar to those, which are Readily biodegradable (generally greater than 70% mineralization of the product).

A chemical, which shows Ultimate biodegradation in this situation, is likely to be considered as Non-Persistent in the environment.

If more accurate information is required on the risk to specific environments, it may be necessary to undertake simulation tests. These are longer-term projects acting as models for actual situations. They must therefore be validated and justified. A failure to show biodegradation after prolonged exposure, renders the chemical as Non-Biodegradable or Persistent.

If a product does not pass the 28-day Readily biodegradable part of the test, the company that owns the product must consider if the Inherently biodegradable part of the test is cost effective to pursue. Sometimes it may take 84 days to determine the results of 'Inherent' biodegradability.

In the U.S., the ASTM committee adopted the OECD 301-B Modified Sturm procedures within ASTM D-5864-00 Standard Test Method for Determining Aerobic Aquatic Biodegradation of Lubricants (originally published in 1995).

This test method covers the determination of the degree of aerobic aquatic biodegradation of fully formulated lubricants or their components on exposure to a bacterial inoculum under laboratory conditions. This test method is intended to specifically address the difficulties associated with testing water insoluble materials and complex mixtures such as are found in many lubricants. This test method is designed to be applicable to all lubricants that are not volatile and are not inhibitory at the test concentration to the organisms present in the inoculum.

A substance known to be biodegradable shall be tested simultaneously with the test substance. For water soluble test substances, suggested reference substances are sodium benzoate or aniline. For water insoluble test substances, the suggested reference substance is Low Erucic Acid Rapeseed oil, also called LEAR, such as canola oil.

The test shall continue for at least 28 days or until the CO2 evolution has reached a plateau.

The levels of biodegradability are listed below in the Environmental Persistence Classification. Ultimate Pw1 is the fastest and highest level of biodegradability. The bacterial microorganisms used in biodegradation tests are some of the simplest forms of life, and like all living organisms, are adversely affected by the presence of chemical toxins. In this test the low toxicity of the test sample is demonstrated by the microorganisms' ability to multiply and biodegrade the sample. Other organizations that have accepted the % theoretical CO2 test method for determining aerobic aquatic biodegradation of lubricants include the ISO, OECD, U.S. EPA, and the EUC.

ASTM D-6046-02, "Standard Classification of Hydraulic Fluids for Environmental Impact"

(Terminology referenced from ASTM D-5864)

 
(a)  Ultimate Biodegradation

The degradation achieved when a material is totally utilized, 100% biodegraded by microorganisms resulting in the production of carbon dioxide (and possibly methane in the case of anaerobic biodegradation), water, inorganic compounds, and new microbial cellular constituents (biomass or secretions or both).

 
(b)  Ultimate Biodegradation Test

A test which estimates the extent to which the carbon in a material is converted to CO2 or methane, either directly by measuring the production of CO2 or methane, or, for aerobic biodegradation, indirectly by measuring the consumption of O2.

Used by U.S. Military:

• Pw1 - Greater than or equal to 60% in 28 days
  Rated Ultimate (ASTM) or Readily (OECD) Biodegradable
   
• Pw2 - Greater than or equal to 60% in 84 days (12 weeks)
   
• Pw3 - Greater than or equal to 40% in 84 days (12 weeks)
   
• Pw4 - Less than 40% in 84 days (12 weeks)
   

The OECD 301B Modified Sturm Test is adequate for soluble and insoluble organic, non-volatile materials. This test measures carbon dioxide evolved and therefore measures only Complete Oxidation; organic impurities will complicate the interpretation of carbon dioxide production data.

Test material is introduced into a flask containing mineral substrate and a bacterial inoculum. After ultrasonic vibration, the flask contents are aerated with carbon dioxide-free air. A control without the test material is run in parallel.

Any carbon dioxide released is absorbed in flasks containing barium hydroxide solution. Periodically, the amount of barium hydroxide solution used is determined by titration with hydrochloric acid. Biodegradation is expressed as a percentage of the total amount of carbon dioxide evolved during the test, (corrected for the control), against the theoretical carbon dioxide that the test material could have produced.

Normally, the test lasts for 28 days. Tests however may be ended before 28 days, i.e. as soon as the biodegradation curve has reached a plateau for at least three determinations. Tests may also be prolonged beyond 28 days when the curve shows that biodegradation has started but that the plateau has not been reached by day 28, but in such cases the chemical would not be classed as Readily biodegradable.

The pass levels for Readily biodegradable are 70% removal of DOC and 60% of ThOD or ThCO2 production for Respirometric methods. They are lower in the respirometric methods since, as some of the carbon from the test chemical is incorporated into new cells, the percentage of CO2 produced is lower than the percentage of carbon being used. These pass values have to be reached in a 10-day window within the 28-day period of the test, except where mentioned below. The 10-day window begins when the degree of biodegradation has reached 10% DOC, ThOD or ThCO2 and must end before day 28 of the test.

The CEC L-33-T-82 (now listed as CEC L-33-A-934) test applies to most organic compounds, whether soluble or insoluble in water. It determines the overall biodegradability of hydrocarbons, or similar compounds containing (CH2) methylene groups, measuring all transformations that the starting material undergoes, including oxidation and hydrolysis. It was developed to characterize the biodegradability of outboard engine oils on the Bodensee, due to the accumulation of mineral oils which tainted fish.

The CEC test is accepted in a number of Blue Angel Environmental Labels, and requires 80% or greater biodegradability. The German Blue Angel scheme does not intend to produce guidelines for Enclosed systems. Despite being convenient and easy, the CEC test only measures the IR absorbance of lipophilic molecules extractable into chloroalkane solvent. Note: It does not measure the water-soluble metabolites which are poorly extractable and therefore, cannot measure extensive degradation or mineralization. This would require a parallel test measuring oxygen consumption or carbon dioxide evolution. There is also no clear structural criterion which can be adopted to compare biodegradabilities of various structure types.

Although the industry, including the ASTM, ISO, OECD, U.S. EPA, and the EUC, is now accepting the % of theoretical CO2 as the method for determining the biodegradation of lubricants.

The CEC method has identified certain trends:

1. Mineral oils, alkylated benzenes, PIB, PAO's polyalkyleneglycols have poor biodegradability, i.e. 0-40%
    
2. Vegetable oils (triglycerides), diesters, polyol esters show good biodegradability, (60-100%). N-Alkyl monocarboxylic acids are common in nature and often appear as products from B-decarboxylation of alkane moieties and they are generally as easily degraded as esters. The degradation products are also more soluble, although the effects on the ecosystem and groundwater contamination are not known.
    
3. Aromatic polycarboxylate esters range from 5-80%. The same molecule can show consistently wide variation suggesting that competent microflora are restricted in their distribution. Polyethers show poor biodegradability in the CEC test, but have the advantage of being water-miscible. Therefore, tests based on oxygen consumption, carbon dioxide evolution or organic carbon removal may be more applicable. By these tests, polyethers are between 0 to 80% biodegradable, depending upon the molecular weight and ethylene oxide/propylene oxide content. Increasing ethylene oxide content and decreasing propylene oxide content give increasing biodegradability.
    
4. Biodegradability is retarded by the particular alkyl chain lengths (C25) and by the degree of chain branching.
    
5. Biodegradability depends upon the available nitrogen and phosphorus in the environment and the inoculum size (if the lab test assessment is made after 21 to 28 days). Certain cultures of bacteria utilize tricresyl phosphate and zinc dithiophosphate as carbon and phosphorous sources. N-heterocycles may act as nitrogen sources and, if so, it may be possible deliberately to formulate blends in which the additives might supply the necessary nitrogen, sulphur and phosphorus for total base oil degradation.
    
6. Additives usually retard the degradation in proportion to their concentration and are themselves poorly degraded, especially heterocyclic structures (triazine, triazole).
    

Summarizing, typical biodegradability values in the CEC L-33-T-82 Biodegradability Test for common hydrocarbons are:

 
(1)  Straight-Chain Hydrocarbon Degradation

In the Aliphatic Fraction, n-alkanes can be completely degraded most readily. At high molecular weights, > C18, n-alkanes exist as waxes, and the rate of assimilation is greatly slowed by the problem of mass transfer of solid substances into cells, although n-alkanes up to C44 can be metabolized by mixed populations of soil organisms. The presence of 1 or more double bonds makes Olefins more resistant to complete degradation, despite the fact that Hydroxylation and Epoxidation of double bonds is well known biochemically.

Cyclo-alkanes are degraded after adaptation of the microorganisms, and resistance to degradation increases with the number of fused rings in the molecule. Structures with 4 or more condensed rings may be co-oxidized in the presence of a co-substrate.

 
(2)  Branched Hydrocarbon Degradation

Branching generally makes an Alkane more resistant to biodegradation. Although Methyl-branched compounds, i.e. Phytane and Pristine are degraded by a number of organisms, they tend to be more persistent than other saturates in crude oil.

 
(3)  Aromatic Degradation

Aromatic hydrocarbons are degraded to form Aryl Acids, but less readily as the number of condensed aromatic Rings increase. Some of the intermediates formed are conjugated and exist as water-soluble Glucuronides and Suphates.

Note:  Ring substitutions can interfere with metabolism; certain metabolized by-products are known Carcinogens.

Aromatic functional groups such as Hydroxyl and Carboxylate groups increase biodegradability, whereas Halogen, Nitro, and Sulphonate groups decrease the rate of biodegradation. Ortho-substituted aromatic compounds are slightly more biodegradable than Para-substituted compounds, and the Meta-substituted compounds have the least biodegradable substitution pattern.

Only simple forms of Polycyclic Aromatics (PCAs) can easily support microbial growth., i.e. Naphthalene, Anthracene, and Phenanthrene. PCAs containing 4 or 5 rings are relatively resistant to biodegradation and previous studies had failed to isolate microorganisms capable of degrading them. A Mycobacterium that degrades Pyrene and other Polycyclic aromatics has now been isolated.

Induction of Enzymes for Polyaromatic Hydrocarbon (PAH) degradation depends upon lower molecular weight aromatics, such as Naphthalene. The finding that the enzymes for degrading at least some PAHs are not induced by the substrate itself is important, and may explain the apparent resistance of these compounds to microbial attack. Although cometabolism has been suggested as the mechanism for enhanced rates of 4- or 5- ring PAH degradation in the presence of 3-ring aromatic hydrocarbons in the soil, it is possible that enzyme induction by the simpler aromatic hydrocarbons is important in determining the rates of higher condensed ring aromatic hydrocarbon degradation.

 
(4)  Asphaltic Degradation

The Asphaltic Fraction is the most resistant to biodegradation and is the most persistent in freshwater ecosystems. Little is known of the metabolism of individual compounds in this fraction. It is probable that some compounds in the asphaltic fraction are not biodegradable, or that they are degraded so slowly that they should be considered Non-Degradable.

An oil may be removed from an area by physical factors, e.g. tides or currents, or it may be covered over by sediment, but some of its components cannot be metabolized and will persist.

Note:  Claims that all oil, or more than 50% of heavy crudes, may be removed by microbial metabolism may be exaggerated. Attack on hydrocarbons by oxygenases produces Free Radicals and other reactive intermediates that may chemically react with each other, forming partially oxygenated, crosslinked, high molecular weight asphaltenes that are quite resistant to further biodegradation.

Striking examples of these Synthetic transformations in the course of petroleum biodegradation are the formation of high molecular weight n-alkanes not originally present in petroleums and the build-up of lipid-rich Petroleum Dirt residue from gaseous Methane by Methanotrophs.

Note:  In soils repeatedly treated with oily wastes, a gradual build-up of biodegradation-resistant hydrocarbons can be observed.