Primary and ultimate biodegradabilities of mineral base oils and their relationships with oil viscosity

We have determined the primary and ultimate biodegradabilities of a series of paraffinic base oils representative of the main classes that are used for the production of lubricating oils, such as engine, industrial, and marine oils. Primary and ultimate biodegrability (B) data were determined using the CEC test and the modified Sturm test (OECD 301B), respectively. There was a strong relationship between the two B values. For a given oil, biodegradation in the modified Sturm test was logically lower than that given by the CEC test. The B values of mineral oils were compared to oil (kinematic) viscosities (KV) known to affect significantly oil biodegradability. Both ultimate and primary B values were linearly related to log(KV).