Impacts of outboard motors on aquatic systems

Outboard motor emissions often are localized in coastal and freshwater ponds, which may make their impact comparable to larger sources that discharge at greater distances from these locales. Outboard motor exhaust gases are rapidly cooled with some fractions being condensed and remaining in the water column rather than being released into the atmosphere. Here the authors compare the hydrocarbon emissions and biochemical effects of 2-cycle vs. 4-cycle engines. The engines were run for the same periods in 30-gallon containers and quantities and identities of hydrocarbons in the water were determined. Polynuclear aromatic hydrocarbons including 2-ring to 5-ring compounds and alkylated derivatives were detected. The concentration of total polynuclear aromatic hydrocarbon (PAH) was 5-fold less in the water from the 4 cycle than from the 2 cycle engine. However, the concentrations of 4- and 5-ring PAHs were not significantly different in water from the two engines. Exposure of killifish (Fundulus diaphanus) to diluted water containing emissions caused an induction of the content and catalytic activity of cytochrome P4501A (CYP1A), a sensitive biomarker for hydrocarbon exposure. CYP1A protein was induced by both, but inhibition of EROD induction occurred with greater concentrations of 4-cycle water. Relating these results to field data for CYP1A in fish from ponds that are or are not exposed to boating activity suggests that boating could account for a substantial part of the induction seen