Tracking Toxic Chemicals in Oil Spills: Does out of Sight Mean into the Air or into Fish?

Article excerpt

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I don't do San Francisco like most people.

I skip the cable cars, Lombard Street, Alcatraz, and the fine restaurants and museums. Soon after my flight arrives, I drive my rental car north over the Golden Gate Bridge and hike uphill a half-mile where I am rewarded by breathtaking views of the Pacific Ocean and steep slopes filled with dry grasses and brilliant green vegetation. But that's not what I'm after. I trek a mile farther down a treacherous slope to a small beach, where I find what I've been seeking.

Rocks. Rocks with oil on them.

Next I drive to a popular coastal walkway to peruse more rocks. The following day I visit a local marina and one of the largest dog parks in the United States where, in addition to rocks, the shoreline is covered with hundreds of broken ceramic dishes--remnants of a ceramic factory closed in the late 1960s. I'll collect anything with oil on it.

On the third day, my search takes me by ferry to Angel Island. I walk briskly around the island's perimeter and make it back to the ferry just in time to catch the return trip to San Francisco. And then to the airport. I know the routine well. I've done it half a dozen times.

At each stop, I pull out purple gloves and foil envelopes and scour the shoreline for oil samples. Passersby offer me quizzical looks; a few stop to ask questions. If my intense staring at rocks and searching in every nook and cranny doesn't get their attention, the purple gloves do.

The M/V Cosco Busan oil spill

The oil I'm looking for on the shores of San Francisco Bay was spilled in November 2007 by a container ship, the M/V Cosco Busan, after it struck the San Francisco-Oakland Bay Bridge. The spill released tens of thousands of gallons of heavy fuel oil into the bay, leaving a dirty bathtub ring of oil along its rugged shores.

The spill affected more than 100 miles of coastline. It killed more than 2,000 birds and may have caused a devastating decline in local herring populations that resulted in the first closure of the bay's only commercial fishery. No one can say with certainty whether this decline resulted from the spill or from natural causes.

One way to explore this question is to look closely at the oil itself to understand its potential toxicity over time. Once released into the environment, the various compounds within an oil can evaporate, or be dissolved into surrounding waters, eaten by microorganisms, or broken down by sunlight. How these so-called "weathering" processes affect different compounds depends on the individual compounds' physical characteristics, including their size and chemical structure.

That's where I come in. That's why my suitcase is always filled with oily samples when I leave San Francisco. Back at the Woods Hole Oceanographic Institution, I am using novel techniques to study the diverse chemical compounds that comprise spilled oil, with the goal of more fully understanding what happens to them after a spill.

All oils are not created equal

Oil is an intimidating mixture of thousands of compounds, and every oil is different. All petroleum-based fuels, including the gasoline we pump into our cars, begin with crude oil that is pulled from the ground and processed at a refinery, where it is heated and separated into the different products we use. As crude oil is heated, lighter compounds evaporate and are collected and sold as gasoline, jet fuel, kerosene, diesel fuel, and lubricating oil (motor oil).

At the end of this distillation process, there remains a thick residue of heavier compounds that were not evaporated off during the refining process, called the residuum. Heavy fuel oil is made from the residuum by "cutting," or adding one of the lighter fuels (such as diesel) to thin the residuum and make it easier to use. Since every residuum is different and the type and amount of cutting oil varies, there is no standard heavy fuel oil. …