Note to Wombats: Don’t Eat the Heliotrope

wombat

Southern Hairy-Nosed Wombat (Wikimedia Commons, photo by Jason Pratt, Creative Commons Attribution 2.0 Generic license)

The wombats didn’t start getting sick until after Australian ranchers moved their livestock off the plot of land that the livestock and wombats had shared, after the foul-tasting weeds took over, pushing aside the tasty native grasses. The older wombats knew that something had changed, but the younger generation ate whatever was available, and they paid for it with liver damage, hair loss, and sun-blistered skin.

Lucy Woolford and Wayne Boardman of the University of Adelaide and Mary Fletcher of the University of Queensland reported recently on their study of ten southern hairy-nosed wombats that lived on a plot of land in the Murraylands near Blanchetown, South Australia, about 130 km (80 miles) northeast of Adelaide. Park rangers had shot five of them to end their suffering, two of them died in an animal rehabilitation center, and three were still alive at the rehab center. All ten wombats were female, five adults and five weaned juveniles.

Australia map

Areas where southern hairy-nosed wombats live. Red arrow points to Blanchetown. (Source: IUCN Red List of Threatened Species)

Wombats, large, burrowing marsupials that live in the southern part of Australia, have had a hard time of it. They have had to contend with agriculture, imported livestock, drought, and disease.

The southern hairy-nosed wombats in the Murraylands have had an especially tough time. Drought and sarcoptic mange (also called scabies, a disease caused by mite infestation) have reduced their population by about 70% since 2002, down to about 10,000 to 15,000 individuals.

Heavy summer rainfall and flooding in 2010 and 2011 damaged feeding areas, and large numbers of emaciated wombats, missing patches of hair, have been sighted since then. Wombats usually feed by night, but after the floods, they have been seen grazing during the day and returning to their burrows before dusk.

The research team examined blood, tissue, and feces from their ten wombats, and they did veterinary examinations on the three that were still alive. The juvenile wombats showed the worst symptoms. Their livers had shrunk, and their gall bladders were inflamed. They were jaundiced, emaciated, and were missing patches of hair on their backs, sides, and heads — areas that were most exposed to the sun. Something had made the wombats more sensitive to sunlight, and their switch to daytime grazing only made things worse.

The team team recognized the symptoms as similar to those they had seen in cows, sheep, horses, and red kangaroos that had eaten certain kinds of poisonous plants. They collected samples of plants from the feeding area for identification and comparison with the stomach contents from the sick wombats.

onionweed

Onionweed, an invasive species. (Source: U.S. Dept. of Agriculture)

Native grasses were scarce in the area where the ten wombats had lived. The area was overgrown with onionweed. Other plants were present as well, but what caught the researchers’ attention was the heliotrope growing close to the wombats’ warrens. Heliotrope has a pretty flower, but it also contains a class of bitter-tasting chemical compounds called pyrrolizidine alkaloids, which cause liver damage.

heliotrope

Heliotrope, the plant that sickened the wombats. (Photo by Carsten Niehaus, Wikimedia Commons, Creative Commons Attribution-Share Alike 3.0 Unported license)

There was ample evidence that the wombats had eaten the heliotrope plants, despite the bitter taste. The researchers speculated that juvenile wombats had eaten more of the heliotrope because it was close by their warrens, and they had not eaten enough native grasses to develop a strong preference for them — they just didn’t know any better.

This is one case where letting the land go back to the wild wasn’t good for the wildlife.

Source: Woolford, L., Fletcher, M.T., and Boardman, S.J. Journal of Agricultural and Food Chemistry, 2014, ASAP, dx.doi.org/10.1021/jf405811n.

These iron curtains are very, very sheer.

graphene

Model of the atomic structure of graphene. Source: Wikipedia, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Recently, a group of researchers in Dresden, Germany found a way to make one-atom-thick sheets of iron. It wasn’t what they had set out to do, but they were alert enough to see this as the intriguing discovery it was rather than an annoying byproduct to be cleaned up.

Thin metal films are used as coatings or wrappings (aluminum foil, for example), components in optical and laboratory instruments, and as chemical sensors and catalysts. For a lot of high-tech applications, including high-density recording media and electronic devices, the thinner the film, the better. The ultimate thin film would be a sheet one atom thick — a monolayer.

Carbon monolayers, known as graphene, have been around for a few years, and researchers have been busy exploring the unusual properties of these ultra-thin carbon sheets. It turns out that structures in which the atoms that are linked side-to-side, but not up and down, conduct electricity very differently than their multi-layer counterparts.

Because of the way that carbon atoms connect with one another, it forms thin sheets very easily. Graphene is just an extreme form of graphite, which is made of carbon sheets that are a few hundreds to several thousands of atoms thick. Graphene was discovered when scientists applied strips of adhesive tape to pieces of graphite and carefully peeled up the top atomic layer.

Making thin layers of metal is a more difficult proposition. Metal atoms tend to form chemical bonds in all directions, forming solid chunks. Thin sheets are formed by pressing metal slabs between rollers or vaporizing the metal and spraying it onto a surface. Applying sticky tape to a piece of metal might pull a few individual atoms loose, but it’s not very effective for peeling up an intact layer.

Also, very thin metal films require some sort of support structure, called a substrate, to hold them intact. That means that only the top of the film is available for use. Until now, a free-standing metal monolayer seemed like an interesting theoretical exercise that would never be realized in the real world.

The Dresden group made their discovery while they were making graphene. They grew graphene layers from a carbon-containing vapor deposited onto a nickel–molybenum substrate. To peel the graphene up from the substrate, they used an etching solution made of iron chloride.

When the researchers examined their graphene under an electron microscope, they found that the etching solution had left behind a residue. Under the microscope’s electron beam, this residue was converted to metallic iron, which formed very small crystals and atom clusters on the surface. Some individual iron atoms were stuck to the edges of holes in the graphene film.

hexagonal iron

Three layers of the type of iron crystal found in this study. Source: Wikipedia, public domain.

What was truly surprising, however, was the appearance of pure iron crystalline layers, one atom thick, suspended across some of the holes in the graphene sheets. Although the widest of these layers was only about ten atoms across, the layers were arranged in an orderly fashion that were definitely monolayer versions of an iron crystal.

The researchers repeated their procedure and examined several iron-contaminated graphene sheets using their electron microscope. They analyzed the structure and characteristics of the iron films, to make sure that these truly were pure iron monolayers. Their observations agreed well with the theoretical properties derived from calculations.

They watched the samples for several minutes each to see how the microscope’s electron beam affected the formation of iron monolayers. They found that, under the beam, iron atoms on the graphene surface moved around and collected in small holes, where they formed crystalline monolayers within a few seconds. The monolayers were stable for several minutes under the electron beam. However, if they left the samples under the beam for longer than that, the monolayers began to collapse to form non-crystalline three-dimensional particles.

Now that they know how to make iron monolayers, the Dresden researchers and their colleagues can try this technique with other metals and see just how large they can make these metallic sheets.

The original research results were published here: Science 2014, 343, 1228–1232
I posted a more technical summary on the American Chemical Society’s Noteworthy Chemistry blog.