The biological degradation of acetaldehyde in coastal seawater

To assess how fast acetaldehyde can be removed in seawater, acetaldehyde loss was measured in filtered and unfiltered seawater collected from Pacific Ocean waters at a coastal site in Orange County, California, USA between January and June 2014. Samples were injected with fully deuterated acetaldehyde, and concentrations measured periodically by purge and trap isotope dilution GC/MS. For unfiltered seawater, measured first-order rate constants ranged from 3.3 × 10− 4 min− 1 to 5.4 × 10− 3 min− 1, with an average of 2.0 ± 0.1 × 10− 3 min− 1. This suggests an acetaldehyde turnover in these waters ranging from 185 min to ~ 3000 min with an average of 500 min. Loss rate constants measured in seawater filtered through 0.2 μm filters (attributed to chemical degradation) were negligible relative to those for unfiltered seawater (attributed to abiotic or biotic particles). First order rate constants in filtered seawater were on average 4 ± 2% of those measured in unfiltered seawater. Unfiltered rate constants increased during regional rainfall events and were positively correlated with aerobic bacterial counts. The correlation was stronger in the wetter first half of the experiment (R2 = 0.873 vs. 0.685). Correlations with bacteria levels and activation/deactivation experiments suggest that the loss in unfiltered seawater samples is driven by biotic particles rather than abiotic particles. Acetaldehyde degradation rate constants are higher than acetone degradation rate constants measured previously at the same site. Comparison with estimated photochemical production rates suggests that these waters are a source of acetaldehyde to the atmosphere.