Photodegradation Driven by Visible Light Exceeds Biodegradation across a Range of Environmental Conditions during the Initial Hours after an Oil Spill

Degradation of oil compounds, mediated by microbes or abiotic factors, after a spill into aquatic environments is important for ecosystem recovery; however, factors controlling these processes in natural waters remain poorly characterized. Six experiments representing a range of environmental conditions measured the loss of n-alkanes and polycyclic aromatic compounds (PACs) from a crude oil over 72 h due to biodegradation and abiotic processes when exposed to visible light. On average, 22.8% (±12.6) of n-alkanes and 32.7% (±14.0) of PACs were removed in the live incubations compared to 19.1% (±19.3) of n-alkanes and 31.7% (±12.3) of PACs when microbial activity was inhibited by the addition of mercuric chloride. Substantial biodegradation was only observed in the warm, freshwater incubation. Additional experiments determined that most of the abiotic degradation could be attributed to photodegradation mediated by visible light. No clear link was observed between the environmental conditions and abiotic losses of oil compounds, indicating complex interactions between light, photosensitizers, and organisms. These experiments demonstrate that a significant proportion of the n-alkanes and PACs may be removed from a surface oil spill through photodegradation mediated by both visible and UV light, along with biodegradation, within a few days.