  Dispersants aid the breakup of crude oil masses and increase the available
interfacial surface area for bacteria to degrade insoluble hydrocarbons in the
marine environment. However, this common view neglects key aspects of the
microscale interactions between bacteria and oil droplets, particularly the
encounters between these elements that are required for degradation to occur.
This chapter discusses a biophysical model for hydrocarbon consumption of
suspended oil droplets under conditions of rapid dilution that occur in natural
environments. Based on the model, which includes typical biological growth
parameters, dilution is found to produce an effective delay in the onset of
biodegradation by approximately a week. The steady and rapid reduction in oil
concertation, due to dilution, is found to outpace the production of
oil-degrading bacteria that result from colonization of degrading oil droplets,
maintaining the process in an encounter-limited state. This mechanistic model
provides a baseline for better understanding of microscale biodegradation in
dilute oil environments and can help inform the design of mitigation strategies
in marine systems.
