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Thread: Climate change linked to rise in mercury levels in some fish

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    Default Climate change linked to rise in mercury levels in some fish

    Amy Norton
    Aug. 7, 2019

    A new study adds to the list of potential health threats from global warming: Higher mercury levels in certain fish.
    While eating fish is considered part of a healthy diet, it's also a source of mercury -- which, in high enough amounts, is toxic to the nervous system and kidneys.
    Small fish generally have only small amounts of mercury. But when larger predatory fish eat those smaller ones, mercury builds up in their fatty tissue. So, health authorities advise against eating certain long-lived predators, like shark, swordfish, king mackerel and tilefish. That's especially important for pregnant women and young children, since the developing nervous system is vulnerable to mercury's toxic effects.

    Keep reading: https://www.upi.com/Health_News/2019...8971565206180/
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    Veteran Member Mr. Wizard's Avatar
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    Default Re: Climate change linked to rise in mercury levels in some fish

    As noted repeatedly here at HH, mercury levels in fish is a totally overblown issue. Most commonly eaten fish contain the mineral selenium, which counteracts mercury. Most fish/mercury studies fail to recognize "mercury binds to selenium," significantly reducing mercury toxicity. Moreover, wild salmon, haddock, pollock, trout, herring, mackerel, shrimp, scallops, and many more commonly eaten fish and seafood contain very little mercury to begin with. Any mercury level increases due to global warming should have little effect on fish/seafood already low in mercury.

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    Default Re: Climate change linked to rise in mercury levels in some fish

    Thank you for the reminder, Mr. Wizard. Some of us have major memory lapses!
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    Veteran Member Maurya's Avatar
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    Default Re: Climate change linked to rise in mercury levels in some fish

    From an interview with Dr Christopher Shade, my favorite mercury expert:

    Chris Kresser: Right. All right, well, let’s talk a little bit about seafood. This is where I think I’m going to get some education from you! I know you don’t agree with or at least you have a different understanding than Nick Ralston, whom I’ve interviewed in the past and talked to at length about the protective effect of selenium with mercury. We were talking about that before the show. Maybe it would be fun at some point to have a kind of roundtable discussion, but I’m really curious to hear your perspective and what I’m missing in this whole understanding of the relationship between selenium and mercury.
    Dr. Christopher Shade: Yes.
    Chris Kresser: And maybe even before we go into that, just talk a little bit about fish and seafood and what the biggest concern is in terms of mercury.
    Dr. Christopher Shade: Sure. OK, so the mercury in the fish is not in the fat. A lot of toxins are in the fat, and a lot of people think it’s in the fat, but it’s actually in the proteins, and again we go back to this story of cysteine, the amino acid that is part of the protein structures, and it has this sulfhydryl group, and the sulfhydryl group has a high affinity for mercury. So the methylmercury sticks to it, and when you eat it, you digest the proteins and you hydrolyze all that protein into amino acids, and then you have free cysteine and it still has the methylmercury stuck to it.
    Now, it just so happens that methylmercury bound to cysteine looks, to your body, a lot like methionine, another amino acid. So you have molecular mimicry and you have absorption of the methylmercury cysteine through amino acid transporters in your GI tract, and that’s why you get 95% uptake of mercury from fish. OK? And then it distributes through the body, and it moves around as an amino acid until it jumps ship from the cysteine and lands on some other binding group, which is usually some other sulfhydryl group.
    Now, it can also bind on selenium groups. The only thing that binds mercury stronger than a sulfhydryl group is a selenol group, which is selenium with a proton on it. And there are analogs of sulfhydryl groups called selenols. So there’s cysteine and then there’s selenocysteine, and selenocysteine is put into some very special antioxidant molecules, like glutathione peroxidase and thioredoxin reductase. One of the targets of mercury are these enzymes, thioredoxin reductase and glutathione peroxidase, and when you knock out all of the thioredoxin reductase, it’s very damaging to the organism because it stops you from being able to replicate DNA and it stops a number of different processes, and so it’s very toxic to the body. And what you need is a constant supply of selenium to then rebuild that thioredoxin reductase and the glutathione peroxidase, these things called selenoenzymes. So selenoenzymes are one of the targets of mercury, but not the only target. And so if your diet is high in mercury and low in selenium, you quickly deplete these selenoenzymes, and that becomes a major aspect of the toxicity of mercury in that situation, where you’re low selenium, high mercury.
    Now, Nick Ralston had been doing some very nice studies where he was selenium depleting—and this is the part that is not conveyed right—he was selenium depleting mice and then feeding them mercury, and they had these toxic manifestations, very bad ones that would kill them eventually. And then he would slowly bring up their selenium status, and they would be less reactive to that mercury. And so when you look at that, it looks like selenium protects you from mercury toxicity, but what it is is that selenium depletion makes you more susceptible to mercury toxicity.
    Now, this isn’t the first time these studies were done. These studies were done back in the ‘70s—maybe it was the ‘80s; I’d have to look back to the studies—and what they found was that the selenium deficient animals were super-susceptible to mercury. And then as they raised them up to selenium repletion in the diet, where they had enough selenium, they went up to a normal susceptibility to mercury. And then as they raised the selenium beyond the nutritional needs, they did not get any further protective effect.
    Chris Kresser: Mm-hmm.
    Dr. Christopher Shade: So it’s not that the selenium blocks all toxicity, but the selenium blocks this extra toxicity that comes about from selenium deficiency. And so when you hear Nick Ralston talk, he’ll talk about fish-eating populations that don’t really have other selenium sources in their diet, and so their selenium-mercury balance was dependent on the fish, and if they were eating low-selenium fish, they tended to have more problems than people who were eating higher-selenium fish.

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    Default Re: Climate change linked to rise in mercury levels in some fish

    That's illuminating, Maurya. The level of detail clarifies what Mr. Wizard has told us. My multi-vite-mineral has selenium, but I take an extra one from time to time and now I can't remember why. But I guess it was a good idea despite my poor memory....
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    Veteran Member Maurya's Avatar
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    Default Re: Climate change linked to rise in mercury levels in some fish


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    Veteran Member Mr. Wizard's Avatar
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    Default Re: Climate change linked to rise in mercury levels in some fish

    Maurya, thanks for the additional info. This quote at the very end from Dr. Christopher Shade says it all: "....., and if they were eating low-selenium fish, they tended to have more problems than people who were eating higher-selenium fish." KEY POINT - one of the key early studies (Faroe Islands study) warning pregnant women to avoid mercury in seafood was based on women who consumed "pilot whale" meat, which is a low-selenium fish. Mercury was viewed as a problem because there was not enough selenium in the fish or their diets otherwise to balance the mercury consumed from the pilot whale fish.

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    Veteran Member grulla's Avatar
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    Default Re: Climate change linked to rise in mercury levels in some fish

    Gosh "maurya", you are awesome at sorting out and understanding much (bio) chemistry, something that I am not very knowledgeable about. I do take one 200 mcg selenium tablet dialy with the rests of my 25-30+ vits. and supp at breakfast. I guess here in NM, the likliehood of mercury in fish is pretty low, unless perhaps from canned fish. And even canned fish (as in tuna) is supposedly very low in mercury because they usually just can smaller, therefore younger, fish that haven't had a chance to get toxified that much in their shorter lifespan, compared to larger, and therefore older fish.

    All this discussion of seafood brings back memories of having grown up in NJ, and ocean fished much for Blues, Fluke and Flounder, Sea Bass, mackerel, blow fish, whiting, and so much more. Today I carefully choose wild caught sockeye salmon at Wally, or fresh cut at Albertson's (now Safeway) meat dept. here in NM.

    And then there was the famous iconic seafood restaurant I remember as a youngster at, you guessed it "Islander", Maine Ave, in pregambling, "Monopoly", Atlantic City, NJ, where the trolleys ran past Hackney's and next door Capt. Starn's seafood restaurants adjacent to the Inlet ocean water front trolley barn, until the end of 1955 when the whole "trolley theme park 'museum'" of so many makes and models of street cars was sadly scrapped...all that nostalgia. Today, so many cities are returning to, or resurrecting, light rail, maybe Atlantic City could also???

    One can scan and navigate all 114+, ocean front sea shore, environmentally friendly, former trolley pix nostalgia. And here are some of those nostalgic seafood restaurant links.

    https://duckduckgo.com/?q=Hackney's+...4b8efbff84.jpg with concrete brine tanks in the kitchen.

    http://www.newdavesrailpix.com/odds/nj/htm/acs073.htm
    http://www.newdavesrailpix.com/odds/nj/htm/acs091.htm Hackney's background
    http://www.newdavesrailpix.com/odds/nj/htm/acs097.htm Hackney's again
    Last edited by grulla; 4 Weeks Ago at 09:43 AM.

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