Is Gulf Seafood Safe to Eat?

High-tech analyses look for oil contamination in Gulf food webs and fisheries

04-06-2011 // Bob Serata

First, there was the sniff test, in which “experts trained in a rigorous sensory analysis process have been testing Gulf seafood for the presence of contaminants,” according to the U.S. Food and Drug Administration (FDA). For many who suspected state and federal agencies were in cahoots with commercial interests to get the seafood business moving again after the Gulf oil disaster, the sniff test didn’t pass the smell test.

Then came the DOSS test, in which NOAA and the FDA decided to test for dioctyl sodium sulfosuccinate, known as DOSS, a major component of the dispersants used in the Gulf.


Results were negative, the shrimp harvest proclaimed safe.

A lot of testing has been done, and there’s more to come. But questions remain about BP’s 206 million gallons of oil and nearly two million gallons of chemical dispersant contaminating some of the world’s most productive fisheries.

A study of the Gulf food web led by principal investigators (PI) Dr. Jeffrey Chanton, the John Widmer Winchester Professor of Oceanography at Florida State University, and Dr. Jennifer Cherrier, associate professor of Environmental Sciences at Florida A&M University, may provide some answers. Chanton and Cherrier together with their Co-PIs Drs. Lia Chasar (USGS) and Kevin Craig (FSU) will use radiocarbon and stable isotopes to trace the invasion of the Gulf oil disaster into Gulf food webs.

An isotope is a form of a chemical element, like carbon or nitrogen. Stable isotopes don’t noticeably decay over time, radioactive isotopes do. Organisms have distinct isotopic signatures — that is, the plant or animal has an identifiable chemical makeup.

You Are What You Eat

To continue this gross oversimplification, an animal is what it eats (or respires). If you know the isotopic signature of a food source and you know the isotopic signature of an organism that ate it, you can trace the source through the food chain.

Crude oil, and especially chemically-dispersed crude oil, is a food source in the sense that it is ingested, sometimes by choice (e.g., by microbes that feed on oil) and sometimes by accident (in the case of animals and planktons that came into contact with BP’s oil).

By performing isotopic analyses oil can be detected in the food chain.


Chanton’s and Cherrier’s objective is to determine and trace the isotopic signatures of carbon, nitrogen and sulpher, which may have come from the oil spill, through the food web — from microbes (e.g., bacteria) to plankton to commercial fishery species like oysters, shrimp and finfish. They’ll also look to trace these signatures in crabs, corals, snails, sediments and peats from near shore and estuary environments.

Deepwater red crabs and coral collected by colleagues during recent expeditions on the deep sea submersible, ALVIN, round out the study.

“This event’s pretty massive,” said Chanton. “We’ve gone all the way to Barataria and Terrebonne Bays in Louisiana and to the Texas-Louisiana border to collect samples. We have some from the Mississippi Gulf Coast, Orange Beach, Pensacola and Apalachicola,” he added.

“The pre-impact [already known] values will then be compared to post-impact values,” said Chanton. “So we’ll try to determine the route and magnitude of oil effects on coastal food webs and fisheries,” he said.

Don’t Have to See it to Believe it

“The beauty of the biogeochemistry, the work that we do, is that we can tell what’s going on in the environment before it gets to the higher trophic levels, before it becomes a huge problem,” said Cherrier.

Cherrier, who is also deputy director of the NOAA/FAMU Environmental Cooperative Science Center (ECSC) noted, “The quickest part of the ecosystem to see the negative impacts is in the biogeochemical level — the bacteria, the phytoplankton, everything that’s really small. And the most rapid way to see recovery is in the biogeochemical data. They’re doing it the quickest,” she said.

“For instance, in Prince Edward Sound, you can’t see any oil there anymore, but the fisheries are still collapsed,” explained Cherrier. “You don’t necessarily have to see something in the system that contaminated it. It’s all dissolved, you can’t see it, but there’s still some nasty stuff there that’s prohibiting the fisheries from coming back,” she said.

The trick, of course, will be to connect unusual isotopic signatures found throughout the food chain to BP’s oil.

“If we do get a signal in some of these critters we would want to do some more control work, like testing older samples and checking out the water to make sure there wasn’t old carbon in the water from runoff or chronic oil contamination in the oysters [from runoff or natural seepage],” said Chanton. “We’d have to do more investigative work just to make sure of that,” he said.

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