Water lettuce and aquatic fern are misnomers for the type of task these plants might be used for in the near future. German researchers recently discovered that Salvinia molesta, an aquatic fern, and Pistia stratiotes, a type of water lettuce, have a specialized leaf anatomy that not only repels water and traps air, but also traps a lot of oil. The leaves of these plants are covered with tiny, hairlike structures called trichomes that allow the plant to float on the water surface and when dried, absorb more oil than two commercial oil absorbents used for oil spill cleanup, Duerex Pure and Öl-Ex.
[The] existing methods of dealing with oil spills all have significant drawbacks. Chemical dispersants and burning can spread toxins around, while environmentally friendly materials like sawdust and wheat straw absorb water in addition to oil, making cleanup messy and inefficient.
These plants offer an eco-friendly cleanup for oil spills that occur from damaged pipelines, oil tanker disasters and accidents on oil drilling and production platforms – and removal of an invasive weed in the process. S. molesta leaves can sop up a puddle of oil in less than 30 seconds.
[Both] the leaves of S. molesta and P. stratiotes absorb more oil than lotus (Nelumbo nucifera) leaves, which have a waxy coating but no hairs. In addition, the synthetic oil sorbents with a hairy texture, nanofur and Deurex Pure, soak up more oil than the non-hairy option, Öl-Ex. These results suggest that trichomes are crucial to oil absorption.
To find out more about how these hairs work, the researchers tested the leaves of four different Salvinia species, each with differently shaped and sized trichomes: short and slightly bent; in groups of four; short and bent, with pairs connected at the tips; and tall, with groups of four connected at the tips. This last type of trichome belongs to S. molesta and is the most efficient at absorbing oil. The connected ends, which give the trichome a shape reminiscent of an eggbeater, play a key role in trapping oil, the researchers say.
These insights could give researchers clues to improve nanofur or create other synthetic substances for oil cleanup. Specifically, instead of designing materials with any old hairy surface, they should aim for long, interconnected hairs that will form pockets to trap oil.
The study also suggests an even simpler potential solution to oil spill cleanup: just use the leaves of S. molesta or P. stratiotes themselves to mop up spills. In fact, harvesting large quantities of these plants would help solve a second problem, since the two species are considered invasive weeds choking subtropical waterways all over the world.
Past studies have suggested that these plants could help remove contaminants like heavy metals, nitrate, and phosphate from water. Now researchers have added oil to that list, which just goes to show that every once in a while, you even have to give weeds their due.
Even though this is a more eco-friendly option for cleaning up oil spills, the hope is that someday there will be no need to use these plants for that purpose.
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