Re: responses written with @gretchengehrke and others as part of DIY Oil Testing Questions:

This is a complex question. Oil pollution can have a variety of impacts on a person’s health, or the health of an ecosystem. In addition to birds and other wildlife getting covered by an oil slick which can result in hypothermia or suffocation, oil is comprised of several toxic compounds that can have severe consequences. Polycyclic aromatic hydrocarbons (PAHs) in oils can impair reproduction, physiological and neurological development in marine organisms, and some PAHs are likely to be carcinogenic in humans (e.g. Pelletier et al, 1995, Samanta et al, 2002). Other volatile components of oil may induce headaches, nausea, and respiratory difficulty during even short exposures (e.g. Solomon and Janssen, 2010). For more information about studies investigation human health effects of exposure to oil, please see this ATSDR reference and this NIOSH reference, both hosted by the national Centers for Disease Control.

Also see the Hazards section of the Oil Testing Kit page.