A lethal combination of oil and sunlight proved unexpectedly toxic to herring embryos after a 2007 fuel spill in San Francisco Bay, virtually disintegrating the developing fish in the water.
Roughly 54,000 gallons of ship fuel spilled into the bay November 7, 2007 when the container ship Cosco Busan hit a tower supporting the San Francisco Bay Bridge. When herring spawned in the oiled waters in early 2008, researchers suspected the fish embryos would develop the heart troubles known from other spills, says environmental toxicologist Gary Cherr, director of the University of California, Davis Bodega Marine Laboratory.
Swelling and malformed hearts did show up in herring embryos exposed to oil at depths greater than a meter in the bay. But embryos from shallower water were “liquefying before our eyes,” Cherr says.
Sunlight reaching embryos near the water’s surface amplified the toxicity of something they absorbed from the ship fuel, argue Cherr, John Incardona of the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center in Seattle and their colleagues. Their report on embryos in the bay appeared online December 27 in the Proceedings of the National Academy of Sciences. Results of lab tests are scheduled to appear soon in PLoS ONE.
Chemists know from lab studies that oil’s damaging effects can be intensified by light, a process known as phototoxicity. “The real question has been, is phototoxicity simply a laboratory artifact or is it important in the field?” says Mark Carls, a NOAA toxicologist and environmental chemist based at Auke Bay Laboratories in Juneau, Alaska. He says the new paper “clearly indicates that phototoxicity can happen in the real world.”
The geography of the bay supports the spill-plus-light explanation for embryo breakdown, Incardona, Cherr and their colleagues contend. Embryos disintegrated in shallow but not deeper, darker water, and followed this pattern even along a coastline with little development and relatively little pollution. In contrast, embryos in both shallow and deep waters looked normal at two spill-free sites, even at one next to the runoff-rich Interstate Highway 580.
In lab tests with zebra fish embryos in various oil-water brews, tissue breakdown started within minutes to an hour of exposure to sunlight. Yet embryos in the dark developed just the familiar slow doom of heart malformations, Incardona and his colleagues reported in the August 1, 2010 Aquatic Toxicology.
In these tests unrefined, or crude, oil didn’t melt tissues, but the common ship fuel called bunker oil did. That’s what the Cosco Busan spilled, a mix that includes the concentrated dregs of refining.
Incardona has yet to figure out which of the many bunker ingredients causes the embryo breakdown. Multiple suspects exist among a group of oil components called polycyclic aromatic compounds that show up in affected embryos but hover elusively around current thresholds for detection, Incardona says.
“I’m actually pretty shocked at the level of the effect they saw,” says toxicologist and fish physiologist Fernando Galvez of Louisiana State University in Baton Rouge. He hasn’t seen tissue breakdown in killifish he studies for impacts of the Deepwater Horizon blowout. Yet he and Louisiana colleague Andrew Whitehead do find health troubles in fish exposed to just a touch of petroleum products.
“A fish that’s safe to eat isn’t necessarily an animal that’s developing properly or growing properly or reproducing properly,” Whitehead says.