Some introduction techniques are proposed, such as direct addition, ultrasonic dispersion, adsorption on inert support, and the use of emulsifiers or non-biodegradable solvents.
Carrying out biodegradability tests on lubricants and greases requires an introduction technique which facilitates the bio-availability of the test substance, reduces the adsorption on the test flask walls, doesn’t change the chemical structure (ultrasonic dispersion), avoids any contamination from the support and interference of a solvent or emulsifier, and maintains homogeneity as far as possible.
Complementary information on the biodegradability of lubricants
The most appropriate test method for lubricants and greases Lubricants and greases are generally poorly water-soluble organic compounds which are classified as difficult test substances and require an appropriate mode of preparation in order to achieve reliable test results.
First, the possible test methods are restricted to CO2 production (OECD 301B or equivalent test methods)
and Repirometry (OECD 301F or equivalent test methods).
Regarding respirometry, the formula of the test substance and its purity, or relative proportions of major components, should be known, so that the ThOD (Theoretical Oxygen Demand) can be calculated. Sometimes, if the ThOD cannot be calculated because the test material is insufficiently defined, the COD (Chemical Oxygen Demand) value may be used to calculate the percentage degradation, but you must keep in mind that this can lead to erroneous results.
The most appropriate biodegradability test method on lubricants and greases is based on CO2
production; this
is the parameter adopted for the recent test method EN 17181, dedicated to fully formulated hydraulic fluids, which also includes the best mode of preparation.
Best mode of preparation ISO 10634 is guidance for the preparation and treatment of poorly water-soluble organic compounds for the subsequent evaluation of their ultimate biodegradability in an aqueous medium.
The best technique for oils and greases is therefore introduction through adsorption on an inert support, followed by evaporation of the volatile solvent used.
Factors which influence aerobic biodegradation Some factors may affect aerobic biodegradation: • •
Branching of hydrocarbon chains
Length of hydrocarbons chains & molecular weight
• • • • • •
• •
Unsaturation
Toxicity against micro-organisms Oxygenated compounds.
Stability (Photolysis – Hydrolysis - Volatility) Presence of substrate (support - binding sites)
Ambient conditions : (Temperature, Pressure, Luminosity, Medium, Presence of nutriments, pH) Interfacial tension with water
Effectiveness of the micro-organisms (enzymatic capacity for the substance to decompose, adaptation of micro-organisms)
• Water solubility •
Heterogeneity
Scope and restriction of test methods OECD guidelines specify that generally, biodegradability tests are intended for pure chemicals; nevertheless; it is relevant to examine the ready biodegradability of mixtures of structurally similar chemicals, like oils and surface-active substances (surfactants). Such substances often occur as mixtures of constituents with different chain lengths, degree and/or site of branching, or stereo- isomers, even in their most purified commercial forms. REACH describes UVCBs, i.e., substances of unknown or variable composition, complex reaction products or biological materials.
Continued on page 24 LUBE MAGAZINE NO.176 AUGUST 2023 23
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