Underwater emissions from a two-stroke outboard engine: Can the type of lubricant make a difference?

The emissions to water from a 1.9 kW two-stroke outboard engine were investigated in the laboratory (fresh water) and in the field (sea water). The primary objective of this study was to characterise and quantify the pollutants that remain within the water column when this type of engine is used. The emission rates of Polycyclic Aromatic Hydrocarbons (PAHs) and Volatile Organic Compounds (VOCs) were determined for the engine when using a mineral and an equivalent rapidly biodegradable lubricant. A further comparison of the emission rates was conducted between the results from the fresh and sea water tests. The results showed that the compounds naphthalene, phenanthrene and benz(a)anthrene that remained in the water were significantly higher than those of other PAHs. The VOCs benzene, toluene, ethyl benzene and xylene were emitted at much higher rates than the PAHs. However, it was found that the fuel, and not the lubricating oils, is the major contributor to these.