Purifying water using the sea…that’s Mike’s and my challenge. But the water we were to purify into drinking water wasn’t sea water; it was water in a cistern-type thing. The concern was that bacteria and other living things would be in it.

I was a bit mystified as to what we were going to do until Mike started rattling off common chemical components of sea water…one of which is iodine. Thinking of the challenge in this way made it possible. Although the concentration of iodine in sea water is too low for us to extract it, some sea-weeds take up and store iodine. So instead of getting iodine directly from sea water, we could use seaweed, which has already done the work of collecting and concentrating the iodine in its tissues - no, I don’t know why it does this - anyone have access to the internet about now?

But how do Mike and I know that sea-weeds have relatively high concentrations of iodine? Health food stores often advertise sea weed as a good source of iodine, plus, somewhere along the line, I read that in the 1800s (I think that’s the right century…) that brown sea weeds were the major source for iodine extraction. Iodine was and still is important to human health as it is a necessary nutrient for the thyroid to work correctly. Look at the label on your table salt - it probably says “iodized salt” just to for this reason. Iodine can be added to table salt without much work and it doesn’t affect the taste.

But we are interested in iodine for its purification properties. Basically, iodine is effective against viruses, bacteria, and most protozoa, all of which can make us sick.

So Mike and I, along with Tony, the cameraman, Simon, the soundman, Rosie, the director, and Hisdory, the local expert on where to find stuff as well as the driver and translator, all piled in the car and headed off to the other side of the island. Though we were on the ocean, this side of Zanzibar wasn’t known for its seaweed.

One thing about looking for plants and animals, even if you know the general area where they should be found -based on habitat - that doesn’t mean they’ll be standing there waving at you. We spent several hours going from beach to beach, combing the water’s edge looking for brown seaweed. Thankfully the tide was out, otherwise we would have been swimming the entire time- a lot of fun, but not a very efficient way to cover a lot of coastline.

We finally found the stuff -various species of brown seaweed. We collected bags and bags of it because none of us had any idea of what concentration would be in the seaweed and how good our methods of getting it out without losing it would be.

Now you ask, why brown seaweed and not red or green or the clear/white seaweed? Basically, we chose brown seaweed because historically that’s what people extracted iodine from. Iodine is probably collected and stored in all seaweeds, but different kinds may take up different quantities. With only three days to do this challenge, we decided to trust those who came before us…use what they used. Otherwise, we could have collected a bunch of different kinds of seaweed, processed them all separated and seen which produced the most iodine per unit wet weight (or dry weight). Not enough time for that though…

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Content last updated: 26/01/2005