Friday, 29 June 2012

Metal Detecting Under the Microscope: They Must Think we were Born Yesterday

In their campaign against putting green waste fertilser onto the fields the metal detectorists of Britain are raising all kinds of alarmist concerns. Obviously they feel that if they say "this stuff is getting into our food" it's enough to get it stopped. So here we get claims like this for agitators:
“The most important principle that you should highlight are the dangers of aluminium mixing with air to create aluminium oxide, which in turn is getting into the food chain.” 
Perhaps not many metal detectorists made it to GCSE chemistry... those who did like the rest of us know that aluminium reacts very readily with "air" (oxygen) to form an instantaneous and fundamentally inert compact oxide film, which then prevents further oxidation. This oxide is so inert that it is used in a filler in plastics (for food packaging, and in toys), it appears in paint, for example probably in the paint on tekkies' cars. It is also used in stuff their wives smear all over their bodies, it's a common ingredient in sunscreen and is sometimes present in cosmetics such as blusher, lipstick, and nail polish. Aluminium oxide is not on the United States Environmental Protection Agency's chemicals lists. The oxide in crystalline form is called corundum, and that's in sander discs and emery paper, it is also what rubies and sapphires are made of. It's also found in some sands, like the sand their kids play in at the beach (there is silicon dioxide and dihydrogen monoxide in this as well as soil). Aren't tekkies a bit worried that this will "get into the food chain" too? Especially the dihydrogen monoxide.

In fact aluminium and its oxides are in all clay minerals which occur in the majority of British soils. And yes, a bit of it gets into plants, aluminium is needed for plant growth. Certain very acidic soils on certain substrates will however have soil water with too many aluminium cations. In such cases, the plant's root systems do not function well, and they (but then also other elements) are not taken up, which then requires the farmer to take other measures. Firstly the knowledgeable farmer would probably not put green waste (whose decomposition products contain organic acids) on such soils, secondly of course soils containing high quantities of non-ferrous metal cations in them are those which in a short term are highly corrosive to buried metal objects, and would not be the sort of places searched by artefact hunters wanting to find collectable stuff. 

Scare tactics of the most base kind, playing on people's ignorance and fears for selfish ends. They should be ashamed of themselves.

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