Is Gulf seafood safe to eat? The Food and Drug Administration (FDA) gave the green light following the BP oil spill that dumped nearly 5 million barrels of crude off the coast of Louisiana last year, but now an environmental watchdog group says the agency's standards are "based on outdated science" and underestimate the risk of cancer-causing contaminants to pregnant women and children eating seafood from the Gulf.

At issue are what the FDA considers safe levels of polycyclic aromatic hydrocarbons (PAHs), compounds found in oil, coal and gasoline that have been linked to cancer in animals and humans. According to Miriam Rotkin-Ellman, a researcher with the Natural Resources Defense Council (NRDC), the FDA accepts 100 to 10,000 times more PAH contamination in seafood than the NRDC deems safe for vulnerable populations.

That conclusion was published online Wednesday in the journal Environmental Health Perspectives. On the same day, the NRDC filed a petition asking the FDA to reevaluate its science and set new limits for PAHs in seafood to ensure public safety, especially for vulnerable populations like pregnant women and children.

On her blog, Rotkin-Ellman noted "six major flaws" in the FDA's assessment of PAHs in Gulf seafood: "assuming everyone weighs 80 kg (176 lbs), underestimating how much seafood Gulf residents eat, ignoring the cancer risk from naphthalene [a common PAH] contamination, failing to address the increased vulnerability of pregnant women and children, allowing for a high level of cancer risk, and assuming that the contamination will only last five years."

Safe standards for PAH contamination, based on new calculations by Rotkin-Ellman and her team, were markedly different from what the FDA found. Wrote Rotkin-Ellman:

"For example, FDA said that 123,000 micrograms of naphthalene per kilogram of shrimp was safe for everyone to eat. According to our calculations, only 5.91 micrograms should have been allowed to protect pregnant women and children who eat a lot of seafood. For comparison, our calculations show that 46.99 micrograms of naphthalene per kilogram of shellfish would be safe for an adult consumer.

According to our calculations, the risk of cancer associated with eating Gulf shellfish contaminated at the levels FDA says is safe could be as high as 20,000 in a million. Put another way, this means that if 1,000 pregnant women (and their children) ate Gulf seafood contaminated at the levels FDA said are safe, 20 of the children born to them would be at significant risk of cancer from the contamination."

The NRDC study found that up to 53% of shrimp tested had PAH levels exceeding the safe limits that the group had determined for pregnant women who eat a lot of Gulf shellfish. Rotkin-Ellman said her study did not find reason for concern for other adults.

For its part, the FDA stands by its calculations and says that seafood fished from areas of the Gulf that have been reopened since the BP spill or were never closed is safe. Reported the Tallahassee Democrat:

"The FDA said most of the seafood it sampled after the spill had no detectable trace of oil. The Louisiana Department of Wildlife and Fisheries and the Louisiana Department of Health and Hospitals calculated that every day for five years the average person could eat 1,575 jumbo shrimp or 130 oysters without health concerns."

"We're very confident that the steps that we have put in place to assure the safety of seafood have worked," FDA spokesman Doug Karas told the Democrat. "We put in an extensive program of sampling, at that time and since then, and the results have consistently been 100 to 1,000 times below our levels of concern."

(By Meredith Melnick*, TIME, 14/10/2011)

* Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME's Facebook page and on Twitter at @TIME.