Report Finds that Land Runoff is the Biggest Source of Oil in the Ocean

Oil can wreak havoc on marine life, from hampering the insulation of otters’ fur to decreasing the reproduction and growth rates of fish. It can also poison a wide array of wildlife if they accidentally ingest it while cleaning themselves. While spills are what typically comes to mind when we think about oil in the ocean, a new report shows they’re not the largest contributor.

The National Academies of Sciences, Engineering, and Medicine has released its fourth Oil in the Sea report, a collaboration with North American government agencies and organizations and the American Petroleum Institute. This edition found that oil runoff from land is the top source of oil in the seas. The amount contributed in this way may also be up to 20 times higher than it was 20 years ago when the last report was released. Sources of this runoff include highways, parking lots, car washing, and motor oil leaks. The oil is carried to the sea through snowmelt or rain.


The report shows that the second biggest source is natural oil seeps, which involve oil entering the ocean through faults and fractures in seafloor sediment. The third largest is oil spills, while discharge from oil and gas operations also contribute.

Though cars are becoming more fuel efficient, there are an increasing number of electric vehicles, and greener sources of energy are expanding, oil remains a big source of energy. This means it will continue to find its way into our oceans, and the report aims to better understand the issue.

Michael Ziccardi, director of the University of California Davis-led Oiled Wildlife Care Network, is on the 17-member committee that compiled the report.

He says, “Over the past 20 years, we’ve learned a lot about the effects of oil on animals and the marine environment, as well as improved our techniques to limit those impacts. This report also shows there’s so much more to learn. While clean energy sources may eventually reduce the amount of oil in the sea, the impacts of oil in the ocean will be with us for a long time, so it’s important we address important knowledge gaps.”


The committee says population growth in coastal areas, more fuel-efficient vehicles, and aging infrastructure impact how much oil runoff makes it to the ocean. Climate change fallout does, as well, including more intense storms and sea level rise.

However, the report says that there hasn’t been enough government action to tackle or understand the problem.

Kirsi Tikka, chair of the report committee and independent non-executive director at Pacific Basin Shipping and Ardmore Shipping, explains, “Since the last time the National Academies examined this issue in 2002, little progress has been made in terms of sustained investment in research that could help us understand how much oil is entering the ocean and precisely where it is coming from. We need this data to ensure efforts to prevent harm to marine life and coastal communities are effective.”


The report’s recommendations include that the U.S. government conduct a thorough review of coastal and offshore energy infrastructure to ensure it can handle more frequent and intense storms fueled by climate change. It also encourages the government to determine if recommendations developed after the 2010 Deepwater Horizon oil spill have been implemented. A third suggestion includes that an independent research group identify which responsibilities should be given to which government agencies in order to collect comprehensive data on ocean oil. That includes where, how, and how much oil is getting into the ocean.

What can you do on a personal level to limit oil pollution? Drive less frequently or choose electric vehicles, limit fossil fuel use in other areas, ensure your car does not have any leaks, properly dispose of used motor oil, and try to avoid purchasing products that contain petroleum or natural gas. You can find out more about such products from the NOAA.

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