Crude oil spill incidents occur frequently, leaving seawater bodies with a verity of occupational, ecological and environmental issues from the local to global scale. Application of sub-surface dispersants to the oil contaminated water in order to break up the oil into smaller droplets has been gaining popularity in recent years as an intervention strategy. However, the use of dispersants may also have impacts on the generation and size distribution of aerosolized droplets, as well as changes in emitted gases when subjected to natural processes such as rains, winds and waves.
In this study, systematic real-time measurements of total VOC (TVOC), particle-bound polycyclic aromatic hydrocarbons (PAH), and aerosol size distribution from 10 nm to 20 μm were conducted over a wave tank containing seawater, seawater plus crude oil, or seawater plus crude oil and dispersant. All experiments were performed using a wave tank (L = 6 m, W = 0.3 m and D = 0.6 m) and sensitivity analyses were conducted on key parameters including wave type, wave frequency and concentration of the added contaminants. Using gas chromatography/mass spectrometry analysis, major VOC and PAH emitting gases were determined to be hexane, cyclohexane, heptane, toluene, benzene and xylene, several of which are known carcinogens. Length of wave stroke was found to be the most influential parameter in increasing the number concentration of nano-sized particles, with the majority of the aerosolized particles smaller than 15 nm. An average of 10 times increase in TVOC concentration in the air above the water surface was observed after contaminating the sea water by 3.5 mL oil-dispersant mixture (dispersant to oil ratio of 1:25) compared to seawater alone. Wave creation led to 40 times increase in TVOC concentration (~400 times higher than the non-contaminated calm sea water). A micro-bubble generating set-up was used to evaluate whether bubble bursting was the generation mechanism of these nano-sized aerosols. Findings from this study will help to assess the risk of exposure to particulate and gases emissions from oil spills both occupationally (e.g., clean-up workers) and environmentally (e.g., people in nearby residential areas).