In 2007, the San Francisco Bay area fell victim to an event called the Cosco Busan oil spill. While the amount of oil spilled was relatively small, the effects on the marine life were anything but minor. Researchers from UC Davis and National Oceanic and Atmospheric Administration (NOAA) conducted experiments to see the effects that the oil spill had on the marine life in the area, and found that herring embryos showed severe abnormalities.
“We did careful assessments to see whether abnormalities were present,” said Gary Cherr, professor of environmental toxicology at UC Davis. “We found swollen hearts and irregular heart rhythms in the areas affected by the oil.”
Cherr said that the oil spill of about 54,000 gallons was about the size of a backyard swimming pool.
“We had a range of very different locations for sampling; some were urban and some were not,” Cherr said. “Surprisingly, the embryos naturally spawned in intertidal zones were dead; they were dissolving, almost unrecognizable as embryos.”
Cherr said that the embryos in the unaffected water were fine; meanwhile, the embryos that spawned in the oiled waters were victim to the worst effects. He said they placed embryos near more urban areas, such as the I-580 Richmond-San Rafael Bridge, as a reference point to see if pollution was a factor in the abnormalities. The embryos by the bridge did not show the severe abnormalities, suggesting that the oil was the culprit.
He said that the cause of the severe abnormalities found in the herring can be attributed to phototoxicity, which is when a chemical leaves an organism much more sensitive to light.
“Oil compounds can be much more toxic in the presence of sunlight,” Cherr said. “This was a situation where you had the embryos in very shallow water and sunlight, so it was a classic example of phototoxicity.”
Cherr said that the herring still showed some very significant developmental abnormalities in 2009 and 2010.
“Concentrations of oil that weren’t lethal became lethal as a result of sunlight,” Cherr said.
John Incardona, supervisory research toxicologist at NOAA, said he was dumbfounded several weeks later, when seeing the results of the natural spawning in oiled sites.
“We were trying to understand what was happening, we were expecting to see subtle differences in their hearts,” Incardona said. “It took a lot of thinking to figure out what could be causing the abnormalities we were seeing.”
Bunker oil is thought to be the contributor to the effects observed in the herring.
“Bunker oil is more chemically complicated than crude oil. Crude oil goes to the refinery, where the lighter products are taken off; the concentrated part goes into bunker oil,” Incardona said.
Incardona said that they weren’t really thinking of phototoxicity as a factor because they had never seen effects like these. He said that phototoxicity had mainly been talked about in lab settings, but that this was the first time where they had seen it demonstrated.
“It’s similar to how somebody takes a drug and becomes sensitive to sunlight. There is something in bunker oil that causes more damage to the tissues,” Incardona said. “All we know is that bunker oil has more of it.”
Carol Vines, assistant project scientist at the UC Davis Bodega Marine Laboratory, also said the results were surprising.
“There were huge mortality rates in the embryos in the oil-affected area. The mortality rate was almost 100 percent; it was shocking,” Vines said.
Vines said that in addition to swollen hearts and irregular heartbeats, they also found that the herring had bent spines, abnormal jaws and some opacity in the embryos — caused by restricted blood flow.
She said that this oil spill was similar to the 1989 Exxon-Valdez oil spill in Alaska, in terms of how the herring population was severely impacted.
“There needs to better categorization of crude oil,” Vines said. “However, we have to keep in mind that this is an isolated incident, and that it is not just oil spills that affect these populations.”
ERIC C. LIPSKY can be reached at firstname.lastname@example.org.