A study published in the scientific journal PNAS (Proceedings of the National Academy of Sciences) says bunker fuel spilled from a damaged cargo in 2007 had an unexpectedly lethal affect on Pacific herring embryos in San Francisco Bay.
The study, published Dec. 26, by scientists from the National Oceanic and Atmospheric Administration and their collaborators, suggests an interaction between sunlight and the chemicals in oil might be responsible.
The issue stems from the November 2007 spill of 54,000 gallons of bunker fuel, a combination of diesel and residual fuel oil, from the container ship Cosco Busan. The spill contaminated the shoreline near the spawning habitat of the largest population of Pacific herring on the West Coast. The Los Angeles Times noted that owners and operators of the vessel agreed in September to pay $44.4 million to cover government claims, cost of the cleanup and restoration programs. In addition to tarring about 30 percent of the herring spawning grounds in the bay, the spill killed some 6,800 seabirds and closed beaches for months, the Times said.
Two decades of toxicity research since the 1989 Exxon Valdez oil spill in Prince William Sound has shown that fish embryos and larvae are particularly vulnerable to spilled oil.
Most catastrophic spills, such as the Exxon Valdez event, involve large volumes of crude oil. However, residual oils used in bunker fuels are the leftovers of crude oil refining, and are not as well studied as crude oils, the study notes. Bunker fuel is used in maritime shipping worldwide and accidental bunker spills are more and more common and widespread than large crude oil spills.
In this study, scientists found that herring embryos placed in cages in relatively deep water at oiled sites developed subtle but important heart defects consistent with findings in previous studies. In contrast, almost all the embryos that naturally spawned in nearby shallower waters in the same time period died. When scientists sampled naturally spawned embryos from the same sites two years later, mortality rates in both shallower and deeper waters had returned to pre-spill levels.
NOAA toxicologist John Incardona, lead author of the study, said based on what scientists know about the effects of crude oil on early life stages in fish, they expected to find live embryos with abnormal heart function, so it was a surprise to find so many embryos in the shallow waters literally falling apart.
“The study has given us a new perspective on oil threats in sunlit habitats, particularly for translucent animals such as herring embryos,” Incardona said. “The chemical composition of residual oils can vary widely, so the question remains whether we would see the same thing with other bunker fuels from around the world.”