Oil spill innovation... from the desert

Cacti could be the basis for a new, non-toxic oil dispersant that could be used on a variety of different oil spills. Photo: University of South Florida
Cacti could be the basis for a new, non-toxic oil dispersant that could be used on a variety of different oil spills. Photo: University of South Florida
The cacti for the new dispersant will need harvesting by robust, commercial machinery... but it won’t compete with food crops. Photo: University of South Florida
The cacti for the new dispersant will need harvesting by robust, commercial machinery... but it won’t compete with food crops. Photo: University of South Florida

Oil spills can be disastrous, but as one pollution response operator put it “you’re damned if you do, damned if you don’t” when it comes to using dispersants.

So, the search has long been on for something that’s lower in toxicity than those currently on the market.

According to chemical engineer Norma Alcantar from the University of South Florida, the gluey centre of prickly pear cacti might be the answer. She told MJ that it was just an offbeat idea at first but when the extract was shaken in a test tube with a sample of crude oil, “within 15 to 20 seconds, the oil had disappeared entirely”.

Why the remarkable result?
The purpose of dispersants is to break up the large globules of oil so that bacteria can get to work; this cactus mucilage contains a whole array of sugars which act as surfactants, creating much smaller bubbles, explained Alcantar: “Given enough surface area, the oil becomes bacterial candy”.

As the size of these bubbles is key to a dispersant’s effectiveness, the smaller the better. Alcantar pointed to a known industry standard, Corexit EC9500A, which creates bubbles measuring between 50 to 75 microns “whereas the mucilage’s are 7 to 50 microns: it really over-performs here”, she added.

Likewise, while toxicity tests on commercial dispersants such as Corexit demonstrate complete mortality of daphnia magna plankton at 34 mg/l within 48 hours, plankton exposed to concentrations up to 1,000 mg/l cactus mucilage (twenty times that Corexit concentration) show a survival rate of 100% over the same time period; “That’s low enough to allow it to be labelled non-toxic,” she explained. And although it requires a 1:50 dispersant to oil ratio – not quite as good as Corexit’s 1:200 – she pointed out “it still competes”.

But the prickly pear has another advantage: “While Corexit has around eight or so different surfactants, investigations have shown our product has about 50 sugars and carbohydrates that work together,” said Alcantar. As a result, it could treat oils with very different compositions, from crude to lighter oil spills from fuel tanks.

More, it won’t compete with food resources: “The cacti doesn’t need much water and it will grow in places that are no use for crops,” she underlined.

by Stevie Knight

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