Slimy mess. But new technology has made tanker spills less frequent.

Most Oil in the Sea From Consumers

Dick writes about Earth and planetary science for Science magazine.

WASHINGTON, D.C.--The "vast majority" of the petroleum finding its way to the sea through human activities now comes from consumers, not from the tanker spills that make such dramatic video, according to a National Research Council (NRC) report released here today. Pollution from tanker spills and other losses during transportation is down by a factor of 10 since the infamous Exxon Valdez spill of 1989. But that decline has highlighted losses during consumption, such as that pesky crankcase drip onto your driveway that eventually finds its way to the sea.

An NRC committee sorted out as best it could how much of the 65 million barrels of crude oil produced in the world every day goes astray and ends up in the ocean. Their estimate: about 20,000 barrels. That's down from the NRC's estimate in 1985, but the vagaries of marine oil pollution make absolute volume estimates tricky. Losses during transportation--including both tanker spills and discharges from ballast and tank washings--accounted for 22% of total losses. That's down from the 42% estimated in 1985. NRC study director Dan Walker attributes the decrease to new technology such as double-walled hulls for tankers and new operational procedures mandated following Exxon Valdez.

By far the biggest contributor--accounting for 71% of marine pollution--was consumption activities, from suburbanites pouring paint thinner down the drain to nontanker vessels dumping their fuel sludge at sea. "The use of oil still results in a lot of it getting into the environment by the drip, drip, drip route," says geochemist John Farrington of the Woods Hole Oceanographic Institution in Massachusetts. "It's the toughest one for regulators to deal with."

These diffuse, largely urban sources have become a particular concern, the report says, because studies of the biological effects of oil pollution show that components of petroleum such as polycyclic aromatic hydrocarbons can have adverse effects on marine organisms even at low concentrations. Oil washed into streams and rivers arrives at estuaries and the coast, areas of particular ecological sensitivity. "Diffuse, chronic releases, such as runoff, may pose a greater threat to the marine environment than was previously recognized," says committee member Nancy Rabalais of the Louisiana Universities Marine Consortium in Chauvin.

Related sites
The report online

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