Weathering of Oil Spilled in the Marine Environment

Crude oil is a complex mixture of many thousands of mostly hydrocarbon and nitrogen-, sulfur-, and oxygen-containing compounds with molecular weights ranging from below 70 Da to well over 2,000 Da. When this complex mixture enters the environment from spills, ruptures, blowouts, or seeps, it undergoes a continuous series of compositional changes that result from a process known as weathering. Spills of petroleum involving human activity generally result in more rapid input of crude oil or refined products (diesel, gasoline, heavy fuel oil, and diluted bitumens) to the marine system than do natural processes and urban runoffs. The primary physicochemical processes involved in weathering include evaporation, dissolution, emulsification, dispersion, sedimentation/flocculation, microbial degradation, and photooxidation.