An unsupportable use of ‘sustainable’

I saw this quote in the December 10, 2011 issue of New Scientist magazine in an article about the rebounding use of guano (bird droppings) as a fertilizer:

“A rise in the price of synthetic fertilisers and the boom in organic foods have renewed interest in guano, a traditional, sustainable fertiliser that is abundant here on Isla Guañape Norte – and many more islands off the coast of Peru.”

The phrase ‘sustainable fertiliser‘ is what struck me. How in the world can a fertilizer be ‘sustainable‘?

The article mentions that there are 4 million seabirds in the area. Say that each produces one-quarter pound of droppings per week (Never before in my life, to the best of my recollection, have I needed to estimate the weight of droppings a sea bird produces. If my estimate seems off to you, then simply change the word ‘week’ to ‘month’ or ‘day’ or whatever other time period makes sense to you). At that rate, the birds would collectively produce 1 million pounds per week.

So, any rate of harvesting that is greater than 1 million pounds per week is not sustainable. Any amount less than that is sustainable.

That is, ‘sustainable’ is a description of the activity of guano-harvesting, not of the fertilizer itself. It is meaningful to say that the harvesting is being done sustainably, or that it is being done in a non-sustainable manner. But to say that the fertilizer itself is ‘sustainable’ is meaningless.

Perhaps the author simply meant that the guano is a ‘traditional, renewable fertiliser’. So let’s just say that.

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