The Use of Liposomes in Biodegradability Testing

An important consideration concerning novel organic compounds is their “inherent biodegradability,” i.e., their propensity to undergo ultimate bio-degradation resulting in C02, H20, minerals and microbial biomass. Inherent biodegradability is typically tested using C-labeled compounds under conditions favorable for microbial activity. This chapter shows that liposome packaging of test compounds offers a way to differentiate true recalcitrance from mass transfer and permeability problems. Alternately, liposomes may be prepared by extrusion through a small pore size filter. This method of preparation was introduced by F. Olson etal. and developed further by M. J. Hope etal. Using a 100 nm pore diameter filter, the average diameter of the resulting liposomes is 70-80 nm. Slightly smaller diameter liposomes can be prepared by the use of a 30 nm pore diameter filter. The extrusion process through a 100-nm pore size filter yielded phosphatidylcholine liposomes containing either 5% pyrene or 1.07% n-octadecane content.