Your world is a toxic, black hole

Your home is your only place of sanctuary. Yet, lurking in the walls is a silent menace. It is a noxious, suffocating, toxic presence, creeping out of cracks and threatening to overwhelm you if you let your guard down. If you venture out to collect food, you face attack: your only option is to flee back to your house, then fight off the danger within.

Fortunately, there are several tools in your arsenal. The strongest is what we all love: good, clear water. The dark menace hates it, because it is transformed into a benign cloud by the oxygen in the water. You’ve developed your defence carefully: your house is designed to flush water through it as you move, creating a protective bubble around you. This chemical battle never ends – your life is a war.

Hiding away from the danger at the surface, surrounded by claustrophic blackness.

Sound familiar? Of course not. We are lucky enough to live in a mostly friendly atmosphere. However, for animals living in sediments (the ground under a water body), the chemicals surrounding them are downright dangerous. They must engage in an ongoing struggle to keep their immediate surroundings livable, while doing all of the usual things – eating, building shelter, and of course, securing the attentions of the opposite sex.

These animals are important for us to study for a number of reasons. For starters, we know very little about how they interact with their environment. More than that, though, their actions – digging, mixing and manipulating – mean the exchange of chemicals from the water to the sediment is much more complex and dynamic than a simple model would assume. Most important chemical cycles – carbon, nitrogen, sulfur and so on – have a substantial part of their global cycle taking place at the interface between water and the soil or sediment, and it’s in these places that the local residents have their biggest say.

On the left, a chemical map of the yabby burrow: on the right, a photo of another burrow.

That’s where my research came in. Working with two great supervisors, I improved a technique for imaging 2D distributions of the highly toxic chemical sulfide (S2-). I also was able to develop a similar technique for looking at dissolved iron, another important sediment chemical. It’s the combination of these two chemicals, into iron sulfide (FeS), which creates the dark black you see in the photos above. When the animals flushed oxygen-rich water into the holes, a thin layer of iron oxide – the rusty orange colour in the photo on the right – would form, creating a very visual clue to the state of the sediment chemistry.

The sulfide method worked a lot like taking a film photograph, but rather than the film reacting to light to form a picture, the sulfide chemical bound straight onto my potassium iodide infused ‘film’ to create an image.

When we applied the technique, we were able to capture dramatic pictures that gave us an insight into the world inhabited by burrowing creatures. The yabby you can see hiding in the top picture was one of our stars: he survived in a sulfide-rich environment for a month, giving us a great sequence of images showing how the whole mini-environment was gradually changed by the presence of his well-tended burrow.

In the rainbow image, the colours represent how intense the sulfide concentration was near the burrow (red was highest). He mostly lived in the central chamber and down the left side, and the plume you can see in the top right is where he started digging a new burrow, which released a stream of sulfide into the overlying water. He had to pump fresh water in, almost non-stop, to neutralise the sulfide creeping into his home.

We take our (mostly) friendly chemical environment for granted, but there are animals living in all kinds of crazy and extreme locations around the world. Their fight for survival is not only an epic tale for each and every one of them, but collectively, they help to shape the world we live in. And we have the audacity to call them shrimp!

ResearchBlogging.orgRobertson, D., Welsh, D., & Teasdale, P. (2009). Investigating biogenic heterogeneity in coastal sediments with two-dimensional measurements of iron(II) and sulfide Environmental Chemistry, 6 (1) DOI: 10.1071/EN08059

Categories: Problems, Science | Tags: , , , | 9 Comments

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9 thoughts on “Your world is a toxic, black hole

  1. It’s funny, we talked about this paper in Microbial Ecology today ;)

  2. bengood4000

    So was this paper written by you or catholic priest David Robertson :)?

  3. Will

    Well, your science communication skills are getting quite good. I felt like I was reading a science fiction novel! Nice work!

    In other news, I did some Fe(II)/sulfide deployments in some large cores of previously homogenised sediment only to find no free sulfide yet! Super annoying! There was heaps of iron (II) though. So I put in some aquarium heaters to get the bacteria cranking along and make me some sulfide….

  4. Nic, heh. And the circle is complete.

    Ben, it was written by the former Major League baseballer. He’s a way better scientist than I am.

    Will, they’re improving… it’s definitely better than my last attempt to explain my research on here about a year ago! Sucks to hear there’s no sulfide. I had that in one core but it flipped in the space of a week or so… went from iron, to not much, to sulfide quite dramatically. How are you managing the method? Any kinks left in it that you haven’t worked out? I always felt like I was playing a delicate game when changing over the probes…

    • Will

      Method is looking good. I’ve calibrated it with higher ferrozine conc (0.01M instead of 0.001M), but that means I need to use the red channel cause green channel is too sensitive. The usable range has gone from 500uM to around 2000uM, which is useful for freshwater stuff, where there is no sulfide to remove the Fe(II). I looked at effect of temperature on color development by doing calibrations at 15deg, 25deg and 35deg, and found very little effect! Essentially the difference between calibs is prob small enough that you can ignore temperature, which is good to know. Preparing a paper at the moment (with you on it of course), so I’ll get you to have a look at it once i’ve got it to 1st draft stage….

      • Awesome! That sounds good. It definitely needed a fresh pair of eyes to change the old ‘I have always done it that way so I will keep doing it’ habits. As with the FM-TOX to some extent, I guess. Keep me posted. Oh and make the most of Autumn. It’s my favourite season on the east coast and I’m jealous of everyone there right now. Warm water, more sunshine, good waves, crisp mornings…

  5. It made me think of what it would be like to live on another planet without our atmosphere – scary

  6. Pingback: Old, old, OLD news « David Robertson


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