The National Oceanic and Atmospheric Administration Fisheries Service says seafood from the Gulf of Mexico is safe to eat. And they aren’t just making that up—there’s test results that back up the decision. But a story at Scientific American explains that there’s a lot of nuance and unanswered questions lingering. What unfolds is a great example of how the same data can look very different, depending on your perspective, and what you know about research methodology.
In the Sci Am story, several scientists outside NOAA explain why they continue to be skeptical of the safety of Gulf seafood. Some of their reasons are fairly obvious—there’s still oil from the Deepwater Horizon spill in the Gulf waters, so a toxicology test from last month doesn’t necessarily tell you anything about the shrimp you eat two months from now. But other problems are less apparent to the average American. Chief among these are the complications of interpreting safety of oil-exposed seafood. There’s a lot in common here with the dose-to-risk comparisons that have people tied up in mental knots over nuclear energy. Worse, though, with oil exposure, it seems that there have been a lot of recent changes to the way we calculate acceptable risk—changes that tend to make us underestimate the threat.
To assess the risk posed by seafood containing polycyclic aromatic hydrocarbons (PAHs), which are known carcinogens, most seafood risk assessments conducted after oil spills in the United States have followed an approach used by the Food and Drug Administration (FDA) in 1990 after the Exxon Valdez oil spill in Prince William Sound, Alaska. The acceptable risk level of cancer from seafood consumption is determined by the quantity of seafood the average individual consumes, the body weight of the average consumer, the average human lifespan, the length of exposure, and the concentration of the PAH benzopyrene. Using this approach, the lifetime cancer risk should be no greater than 1 in 1,000,000.
However, the FDA is now using a less rigorous standard than it did in 1990 – one that tends to underestimate how much seafood Gulf residents actually eat.
“For the Exxon Valdez, there was more awareness of high levels of seafood consumption in local populations,” says Solomon. “They used local fish consumption rates to estimate what levels of contaminants were safe or would be excessive. In contrast, with the Gulf oil spill, FDA used national seafood consumption rates that don’t reflect what people on the Gulf Coast are eating.”
“The assumption that they’re using […] is not as protective of human health as the one that they used for the Exxon Valdez,” says Solomon.
The current FDA risk assessment protocol is based on a 176-pound man eating four shrimp a week. That doesn’t account for women or children, whose body weights are lower, let alone local seafood consumption along the Gulf Coast. “Nobody in the Gulf really eats four shrimp a week, so it’s unrealistic the way they are assessing risk of consumption,” says Shaw.