This week’s post comes courtesy of an email from my Dad, so once more, I’m not really doing my own research and my life has been made easy by fortunate coincidence. My topic this time, by pure chance, is sugar.
So, what on earth has sugar got to do with science, I hear you ask. Good question. Well, actually, you were probably all made to learn the structure of glucose (C6H12O6 etc.) and all that aerobic respiration and photosynthesis business, which is all very well and quite interesting if you’re into that kind of thing. But you can all look up your notes on that, if it so takes your fancy, or Google it if you really want to know. I’m more interested in a particularly novel and different use of sugar by an environmental consultancy firm.
My Dad works in the building industry and somehow stumbled against this very interesting and unusual use of sugar in dealing with contamination of a site with hexavalent chromium and chlorinated aliphatic hydrocarbons. Hexavalent chromium (Cr(VI)) is chromium metal in the +6 oxidation state and is known to be a carcinogen, particularly affecting the lungs via inhalation. It’s also a pretty nasty irritant affecting the skin and internal organs if ingested. The sulphate system takes Cr(VI) into cells, where it is reduced to Cr(III) (Chromium in the +3 oxidation state) and then it is thought that some nasty radical chemistry occurs to damage the cell, leading to cancer and other horrible illnesses. So we don’t really want it in the ground, or anywhere near us, thank you very much. Chlorinated aliphatic hydrocarbons, such as 1,2 dichloroethane, are also carcinogenic and again, definitely not wanted.
But how to get rid of these things in a safe and effective manner? Call in the chemists! The company concerned, RSK, (website found here: www.rsk.co.uk) decided to go for a large-scale injection of molasses into the affected area. Molasses is a by-product of the sugar refining process and is used in cattle feed, or, if from cane sugar, can be used in baking. Molasses from sugar beet contains sucrose, glucose and fructose. Bacteria use these sugars as a substrate for aerobic respiration, depleting the oxygen levels in the soil. This creates a highly reducing environment and the Cr(VI) is reduced to Cr(III) which precipitates as the hydroxide Cr(OH)3 and can be filtered out of the groundwater. Easy! The reducing environment is also helpful in tackling the chlorinated aliphatic hydrocarbons, as they are reduced step-wise to ethane, ethene, and CO2 and water. These gases diffuse out of the groundwater and are pretty much harmless. Some clever and careful planning was required to get the conditions just right for the degradation of the chlorinated aliphatic hydrocarbons but the process required no complex chemicals and was definitely economically viable. I was really impressed with the use of something that can be found in my store cupboard at home to tackle a real, scientific problem. You could call it sweet success!
