Oysters, With a Side of Mothballs

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Source, Vanessa Pike-Russell's Flickr photostream.

No, this is not a bizarre recipe. First, the good news. Extensive testing of seafood from the Gulf shows that "99%" are safe to eat, despite the fact that the fate of some one million barrels of oil from the BP Deepwater Horizon oil rig is unknown.

From Chemical & Engineering News:

...there almost never were any detectable findings of the dispersant in the fish flesh," Kraemer said. FDA and NOAA reported that all samples passed sensory testing and that LC/MS/MS showed no detectable residues in 99% of samples. For the 1% that tested positive, DOSS levels were less than one-thousandth of the LOCs {Levels of Concern.}

"Testing showed that the levels of arsenic, cadmium, lead, and mercury were consistent with the background levels found in seafood not impacted by the oil spill and do not present a public health concern," the agency {FDA} states.

Where did all that oil go? Here's a summary:

The explosion of BP's Deepwater Horizon oil rig caused 4.9 million barrels of oil to be dumped into the Gulf of Mexico. Of that total, an estimated 17% was recovered and close to 8% was skimmed or burned off. More than one-third is believed to have evaporated, dissolved, or dispersed naturally, and about 16% was dispersed chemically. The fate of the remaining oil--roughly 1 million bbl--is uncertain.

Now the not so good news. There is controversy about what exactly defines a "level of concern" (LOC) for given contaminants from the oil spill, and these thresholds have changed over time, depending upon the spill. Even worse, there is debate as to which contaminants may or may not cause cancer, such as naphthalene, a major component of mothballs.

Beyond the high LOCs, NRDC {National Research Defense Council }takes particular issue with FDA's failure to categorize naphthalene as a cancer risk. This occurred, Rotkin-Ellman says, "despite the fact that the National Toxicology Program has listed naphthalene as likely to be a carcinogen, and it is considered by the state of California to cause cancer."

When it comes to specific PAHs such as naphthalene, most Gulf data show levels not only below LOCs but even below detection limits, Gohlke says. This is encouraging, but "you can't do any kind of time-series analysis because you don't have any data to work with on the individual PAHs," she adds.

Below is a summary of the Levels of Concern for oil contaminants in seafood:

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Note that the levels of concern for naphthalene in oysters is 133 parts per million. According to one study, you can smell this chemical at levels as low as 0.08 parts per million. This is why seafood samples are normally tested for this type of contamination using "sensory screens" - in other words, using high trained inspectors who can detect certain odors of a broad range of chemicals, usually at levels as low as 10 parts per million. The technology used to measure contaminant levels in food is becoming more and more sophisticated and reliable, but the nose knows!

More like this

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Great Article, Seafood provides our body the essential nutrients & it's the best alternative to lean meat & should be included in daily diet.

A couple of minor comments:
- The 0.08 ppm concentration for smelling naphthalene is presumably a concentration in air, which isn't comparable to a concentration measured in seafood.
- The reason naphthalene isn't grouped with the "cancer-causing" PAH isn't because they don't think it causes cancer, but rather because the doses associated with cancer are higher than the doses associated with other effects. Unlike "classic" carcinogens, naphthalene generally isn't believed to cause cancer by interacting directly with DNA, and cancer is only associated with high doses. There remains some controversy about the mechanisms of naphthalene carcinogenicity though.

It's also important to note that the levels of concern are based on relatively normal eating patterns. In theory they might not be protective for someone who eats excessive amounts of seafood on a continual basis. In general though I wouldn't really expect to see high PAH concentrations in fish and higher organisms - they are generally metabolized quite rapidly. In my experience the only times I've seen high levels of PAH measured in animals is when they've been directly exposed to the oil itself (i.e. actually coated in oil - typically fish & birds that were killed by the oil or rescued from an oil slick).