So these are the varieties of fish that we looked at for our seafood study here. We had some fresh tuna, some fresh wild Alaskan salmon, some farm raised organic salmon, we had some frozen tuna, some marlin steaks, swordfish steaks and a fresh black pearl salmon.
Samples of these different fish were taken and digested using high purity nitric acid, peroxide and distilled water. After the digestion, they were diluted with more distilled water and then diluted one to ten before analysis doing ICP and ICP-MS.
With our ICP and our ICP-MS we were looking for trace metals and we were looking for a major toxic metal such as mercury. We used reference materials that we create here at SPEXCertiprep. We have some certified reference materials that I had listed here and we use these to calibrate over the expected concentration range of our sample. We also did sample matrix matching for these standards. We also had a NIST certified standard which we processed along with our fish and analyzed as a control.
This is a table of some of the results that we found in our various fish sample. Some of these are very positive elements to have in your diet such as calcium, iron, potassium, magnesium and you can see there’s a wide range of results for each of these elements, and in general is a very good source of things like potassium and phosphorus. There’s also some different ranges of numbers for iron. Tuna has a very large amount of iron compared to the black pearl farm-raised salmon. So if you’re looking for more iron in your diet, the dark tuna would have been a better choice here.
If we look now just for the mercury, if we look at a typical four ounce serving in micrograms, we have a large range of mercury that we found in our different fish sample. Our salmons were virtually identical between three and a half and five micrograms in a four-ounce serving. Now if we look at the allowable daily limit of mercury, this is based on a normal adult diet, we will be hitting about 63 almost 64 percent of an adult, a daily serving of mercury for these different salmon samples.And without be about between six and nine percent for a weekly allowable daily lmit, or allowable weekly limit. But if we get down now to these marlin steaks and swordfish, the game fish, we’re looking at fish that are very slow growing. They are fairly long-lived. They have a longer chance and a better chance of these materials collecting in their tissues. You start to have much higher mercury results. In fact, the swordfish steaks had a 111 micrograms in a four ounce serving and the marlin steaks have way over 300 micrograms in a four ounce serving. So what does that mean if you’re going to eat a marlin steak or you’re going to eat a swordfish steak? Well, you should be aware that the percentage of your allowable daily limit for that swordfish steak will put you way over the thousand percent. So you’ve exceeded your daily limit by a thousand percent by eating that swordfish steak. And you’ve exceeded your weekly limit by almost 200 percent. Now for marlin steaks, the news is a little worse, actually a lot worse. If you look at how much you’re allowed in a daily serving of mercury, if you ate that marlin steak you would be in the 4000 range of how far over your daily limit you were. And in your weekly limit, you would be close to 600 percent over your weekly limit.
There’s an interesting mercury calculator at this website here and you can actually put in your weight and the type of fish you’re planning on eating, and how many ounces of this fish you plan on eating this week, and according to the EPA and the FDA studies, and the EPA data, it will show you how much mercury exposure. You can create your own little table of what your percentage of your weekly limit would be.
So what did we find for mercury content? Well, there were no real differences in the mercury levels between the different types of salmon. And when it comes to tuna, we found that the frozen tuna actually had higher levels of mercury than our fresh tuna. Another interesting thing that we found out about the seafood samples that we are looking at, it seems that the higher the mercury levels we found, they were for again game fish or very dense type of fish, things like swordfish, marlin steaks and shark. And both of the swordfish and marlin steak exceeded EPA guideline limits. Going back to the tuna, imported tuna also seemed to have a higher level of mercury than US tuna. If we look at the studies around different imported tuna, Asian tuna was the lowest of the imported tuna when it regards to mercury and Latin American tuna were the highest and sometimes exceeding the legal limit of mercury.
And we come to the Selenium Paradox. Selenium is an essential element in the human diet and when we consider that mercury is a dangerous toxic element potential in fish, we have to consider mercury alone is not just an at risk indicator there. There are things that can offset the mercury. There are other elements that interact with mercury and Selenium has a very high binding affinity for mercury. Now when the Japanese studied that showed that adding Selenium to the diet of birds actually decrease their protection from mercury toxicity. As I said before, Selenium is a very important mineral in the diet. It’s necessary for cellular function and enzyme creation. And in the body, there is a selenium dependent enzyme synthesis.
There was a study done on Madison Wisconsin fish that shows the different ratios that were found between the different types of fish and selenium and mercury. If we look at this one red line here, this is the one to one ratio where the level of the selenium and mercury are basically equal. And so you quite a bit of the protection or the aseptic protection of the selenium. So when you look down at this very end of the table here, here you’ll find the more game fish, the mahi mahi and the swordfish, the other dense and slow growing fish where it has high levels of mercury to begin with, but they also have low levels of selenium. So you have this ratio which is very close to one and it has the least amount of protection from selenium. If you go to the other end, you have more of these fast growing smaller fish, the cod, and the trout and the white fish, where these ratios are much higher.
We looked at our own samples that we did here at SPEXCertiPrep. We found that salmon had a ratio, selenium and mercury ratio, between four and 11. Tuna had a ratio between three and 10 with the Wisconsin study reporting for the similar tuna, between two and 25. The game fish for us, has a ratio of less than one. So it shows a very low ratio between the selenium and the mercury. And for the Wisconsin study, that swordfish had a ration of one.
So what can we conclude about seafood? Well, with regards to mercury levels, the marlin and the swordfish had the highest mercury levels and in this case they actually exceeded the EPA’s reference dosage limits of the day. For tuna, we found that frozen tuna actually had higher levels of mercury than the fresh tuna. And imported tuna has higher levels of mercury than domestic tuna. If you were going to eat imported tuna, it was found that Asian tuna levels were the lowest of the import tunas, while South American tuna had the highest level of mercury of all the import tunas. So the health benefits of eating fish, do they outweigh the dangers? There’ve been many health studies that shows that the benefits of eating fish actually decrease your mortality rate. So, there’s a statistic that mortality rate for heart disease was actually 30% lower from those eating fish twice a week , than those who do not eat fish. And the overall mortality rate for those who do eat seafood were about 17% lower.
The EPA and the FDA make recommendations for fish consumption, and there’s a nice little chart from the Bureau of Health Environmental Toxicity Program here which has a little diagram of the levels of mercury in each of the different types of seafood. And down here at the bottom with very high mercury are these game fish, the swordfish and the shark, and up to the top where, are the shellfish, flounder, pollock and the cod, these smaller, lighter fish. So the FDA and the EPA advised that you avoid shark and swordfish and other types of game fish like marlin and tilefish.The alternatives are things like canned light tuna, salmon, pollock, catfish. And they suggest you eat up to 12 ounces or two average meals a week of seafood that is low in mercury. They also say that if you eat locally caught fish, please check your advisory for the safety of those locally caught fish. And if there is no information available, eat less than six ounces a week of these locally caught fish.
SPEX CertiPrep analyzed a variety of gourmet foods to discover whether or not they contained hazardous levels of toxic metals. We analyzed Fish, Gourmet Salt, and Chocolate. This webinar was recorded on 6/24/09. Part 2