I've heard that sea salt is more flavorful than iodized table salt, but was wondering about its mercury content.

Due to the mercury level in oceans, nutritionists are recomending to limit sea food meats such as tuna and cod for women who are pregnant. However, do I need to be concerned about mercury when consuming sea salt ?

I'm not much familiar with the techniques used to separate out the salt.

  • really thin pools of ocean water, water evaporates what is left is sea salt--one technique. Water can also be boiled and evaporated this way. These are methods I know of, but these methods may not be how they extract sea salt commercially.
    – Chef_Code
    Commented Apr 15, 2015 at 5:52
  • @Chef_Code : they call them 'evaporation ponds'. if you search for videos, you'll find one from Cargill saying that's the technique they use: youtube.com/watch?v=B8rlLb4zYeY . Of course, they also say that there are microorganisms that 'disappear' as the water evaporates. (and by 'disappear' I assume they mean 'stop showing color' as opposed to 'miraculously leave the brine')
    – Joe
    Commented Apr 15, 2015 at 23:46

2 Answers 2


Food grade salt (Sodium Chloride) in most parts of the world is evaporated from sea water. It generally does not have any detectable mercury, though it does have many other trace elements, some of which are normal dietary minerals

Mined salt (rock salt) is generally used for industrial purposes and de-icing, it contains "dirt", but generally not mercury. In most cases, rock salt is salt from old sea water when it was trapped and evaporated millions of years ago, so has the similar trace elements as fresh evaporated sea water

Some 'speciality' salts, like Himalaya salt, are just rock salt deposits that are more contaminated than normal. Some of these contaminants are normal dietary minerals, most are not e.g. Iron oxide

One interesting exception is the mineral Iodine. It is usually added to food grade salt (fresh evaporated or old rock), as it does not often appear naturally, and many people in the world have diets that are deficient in it

Mercury salts exist in sea water for only a very short time before it is bio-accumulated by algae and then eventually by large order fish. Most heavy metal salts do not stay in sea water for any length of time, but are quickly absorbed by other organisms

  • Nice. I've always wondered why salt was chosen to be the transmitting agent for iodine? Have you found that in your research?
    – user6591
    Commented Apr 16, 2015 at 13:35
  • @user6591 Iodine tastes really crap, salt masks the taste. It's still only dosed at about 0.00003%
    – TFD
    Commented Apr 16, 2015 at 21:10
  • 1
    Your statement Food grade salt in most parts of the world is evaporated from sea water is factually incorrect (that does not take away from your answer to the question, though). Even when named 'sea salt' it often is mine salt. Whether the producer gets away with this depends on (labeling) legislation, hence country. Reference, although this is Dutch you'll get the gist.
    – user34961
    Commented Apr 17, 2015 at 19:52
  • @Jan Doggen Can you provide an actual reference to this? If you read the various salt producer association yearly summaries, you find out that few countries produce rock salt, and when they do it all seems for industrial use. The other 100+ countries in the world use evaporation. From saltinstitute.org "Among the three technologies, most producers around the world are engaged in solar salt production". For USA minerals.usgs.gov/minerals/pubs/commodity/salt/… . The world is a big place; what USA, China, and the Netherlands do is not representative of it
    – TFD
    Commented Apr 18, 2015 at 6:35

Mercury builds up in tuna to significant levels thanks to them eating thousands of critters that in turn eat thousands of critters with tiny little bits of mercury, and it all adding up. It's not about mercury levels in the ocean, per se. It's also a heavy metal so it's not likely to be simply floating around in the water that is evaporated to retrieve the salt.

Despite that I suppose it is possible for mercury to be trapped in little bit of critters that do float around in the water, though. On researching this I have not been able to find anything in the way of proper studies, though I did find lots of alarmist blogs and one company trying to sell heavy metal test kits. I did also find this analysis which is at least slightly scientific; it finds negligible levels of mercury and cadmium in sea salt.

  • 2
    Thanks I also found the alarmist blogs which did not seem creditable; the analysis link you provided is relevant though I was hoping to see an entry for the Celtic brand of sea salt. Like you said, Mercury and other heavy metals amounts were negligible in sea salt in that study.
    – pmagunia
    Commented Apr 15, 2015 at 2:19

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