Testing of imported seafood a fishy business

>>> we are about now with an nbc news investigation tonight. as you watch this next report, keep this one fact in mind. 80% of the fish and shrimp we eat in this country is imported. 80% of it shipped here from overseas. tonight, our investigation has found some of that seafood may contain toxic chemicals and may cause serious health issues over time . our report from nbc 's jeff rossen .

>> reporter: this video, shot by a u.s. advocacy group , shows dirty sewage water to raise shrimp in vietnam . boosting production and driving down cost. would you consider this a public health threat?

>> absolutely.

>> reporter: ron sparks is the commissioner of alabama's department of agriculture . one of the only states testing imported seafood for these dangerous drugs.

>> in some cases, between 40% and 50% of our tests would come out positive.

>> reporter: all targeting seafood with the worst record of contamination, shrimp, catfish, crabmeat and talapia, imported from china, taiwan, vietnam , malaysia, and indonesia. in some cases, officials say ending up in our country's restaurants and grocery stores .

>> unfortunately, consumers can't tell if any of these compounds are in their seafood . you can't smell it, you can't taste it or cook it out.

>> reporter: how dangerous are these chemicals? over time , eating this tainted seafood could cause anemia, cancer, even birth defects. the fda says the risks are long-term and not fully understood. while the fda is responsible for keeping the nation's food supply safe, our nbc news investigation found it tests less than 2% of imported seafood . does the fda need to do more?

>> i would certainly suggest that the fda do more.

>> reporter: the fda declined to speak with us on camera but said it's doing the best it can, targeting its testing on companies and countries that are repeat offenders and rejecting their products until proven safe. john conley runs a trade group represents the imported seafood industry.

>> the fda says it's still coming in with toxic chemicals, it's been a problem for years and it's not stopping.

>> to say any unauthorized use of antibiotics is inappropriate. the vast majority of seafood coming in does not exhibit any problems.

>> reporter: he says the problem is being overblown as a trade issue. he says this video is misleading. instead, he gave us his own video, a picturesque fish farms in vietnam . but when you buy seafood , chances are you don't know where it comes from. while federal law requires grocery stores to disclose its country of origin .

>> where is the tilapia from.

>> reporter: in restaurants, where most of us eat our seafood , it's a different story. most states don't rye you to tell where it's from at all. don't i have a right to know where my seafood is coming from.

>> consumers should feel comfortable fda does a good job.

>> reporter: some officials say consumers are at risk. jeff rossen , nbc news, new york.