Monday, June 6, 2016

Burning seaweed to make glass and avoid a lumpy neck

Seaweed is one of those tricky biological groups, as membership isn't just about being a close relative. It typically includes plant-like organisms found among several types of algae - green, brown, and red - and depending on who you're talking to also includes masses of cyanobacteria (which are distant relatives of algae). Functionally, all seaweeds enjoy growing in salty water and use the sun to manufacture sugary meals for themselves. Their need for sun means they are found in sunlit coastal areas as opposed to deep dark waters.

Seaweed is eaten in such diverse locales as Wales, Japan, and Belize. Agar, the gel upon which microbes are typically grown in a lab, and carrageenan, used to stabilize and thicken a diverse group of products including shampoo and soy milk, are derived from seaweed.

Irish moss is a drink is made from Gracilaria seaweed (Source)

Historically, certain seaweeds were collected, dried out, and then burned in large quantities to reduce them to ash. Two useful substances, sodium carbonate and iodine, could then be extracted from the ash.

Sodium carbonate has many applications but is perhaps best known for being an ingredient in laundry detergent (it's a builder, meaning it softens water and thus makes surfactants more effective at removing oil and grease) and silica-based glass (it serves as flux, drastically reducing the temperature required to melt the silica, also known as quartz sand). During the 18th century and early 19th century, most flat glass had a slight blue-green colour because it was being made using seaweed ash. The development of a cheaper means of sodium carbonate production (the Leblanc process) led to a decline in the use of seaweed in glass production. It's possible to identify seaweed glass by its relatively high strontium content, which is the result of this metal being present in seawater and absorbed by seaweed as it grows.

Iodine, a relative of the elements bromine and chlorine, was first discovered in the early 19th century when a French dude noticed that treating seaweed ash (after washing it with water to extract the sodium carbonate) with sulfuric acid produced a vibrant violet vapour (iode is French for violet-coloured). Here's a video to give you an idea of how this went down. As is the case with strontium, iodine is taken up by seaweed from the surrounding seawater as it grows. Iodine went on to be used as a disinfectant (after being dissolved in alcohol or water) and a means of treating goiter (thyroid enlargement due to iodine deficiency, which results in a swollen neck). It was obtained from seaweeds such as Fucus vesiculosus (bladderwrack), a common inhabitant of the coasts of northern Europe and traditionally used to treat thyroid problems. Iodine deficiency is particularly uncommon in Japan on account of seaweed featuring prominently in Japanese food. However, eating too much seaweed (often due to taking pills of it as a supplement) can cause the thyroid gland to go nuts (hyperthyroidism) on account of the large amount of iodine introduced into the body.


Di Matola T, Zeppa P, Gasperi M, Vitale M. 2014. Thyroid dysfunction following a kelp-containing marketed diet. BMJ Case Reports. DOI: 10.1136/bcr-2014-206330.

Fuge R. 2007. Iodine deficiency: An ancient problem in a modern world. AMBIO 36(1):70-72. [First page]

Ulbricht C et al. 2013. Seaweed, kelp, bladderwrack (Fucus vesiculosus): An evidence-based systematic review by the Natural Standard Research Collaboration. Alternative and Complementary Therapies 19(4):217-230. [First page]

Zava TT, Zava DT. 2011. Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis. Thyroid Research 4:14. [Full text]

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