One of the main tenets of the New Age pseudosciences is that we and everything around us are all part of a greater whole, working in concert and connected by a mystical energy or life-force operating with the four classic elements - earth, wind, fire and water. While the idea of a life-force held within the molecules of living things was generally discarded in the nineteenth century when Wohler created urea in his test-tube there is still perhaps some truth in the idea that we are part of a greater whole. That whole to the scientist though is the massive chemical ecosystem of our planet and beyond it the energy source and entropy drain that is our nearest celestial neighbour the Sun. The idea finds its logical conclusion in the Gaia hypothesis in which our planet is viewed more as a superorganism than a collection of individual systems. Even assuming the bare essentials of this concept can lead to some interesting ideas.
Biologists perceive this world system as being driven by the living things within it perhaps doffing their collective cap only to the molecular on the scale of controls such as DNA and proteins. While chemists often view living things as being driven by the molecules themselves. There is an element of truth in both perspectives where biological evolution proceeds through chemical changes - mutations, deletions and transpositions in the coils of nucleic acid - and living things respond blindly by altering their environment so that only those with chemistry suited to that environment survive intact to perpetuate the story.
There is an alternative viewpoint that takes both sides of the story to a more fundamental level. The presence of a mere twenty or so chemical elements and how they interact in ways far more complex than the simple stoichiometric reactions of the average test-tube are available to life and have been since the time of its inception. This underlying physical chemistry has yielded and continues to yield evolutionary diversity but as we upset the balance, evolution may begin to have an unexpected impact.
The earth settled down early to an iron core, an oxide, silicate and sulfide mantle, an atmosphere of oxygen and nitrogen, and a thin smear of oxygen dihydride over two thirds of its surface. To reach this state the various other elements underwent a selection process through inorganic phase changes and competition between elements for sites in crystalline materials. Chemical affinities, electronic configurations at the fundamental level forced some elements out of the emerging picture while others were placed in optimum states for further reactions including those involved in life. An unsuitable oxygen affinity and the element was effectively selected out by either becoming locked away in deep rock or boiling off into space leaving behind the twenty or so common ones from which emerging life then chose.
As life began to emerge, each of those elements found a place in the chemistry of life and the selection of the elements has been sufficient for all life until now. Each member of the list, which includes, carbon, iron, hydrogen, zinc, oxygen, nitrogen, calcium, potassium, chlorine etc were selected as a particular element found a niche within an organism and fulfilled a role that better equipped the organism for survival and reproduction in its particular environment. Human activity, however, has moved well outside this grouping of elements. We evolved with twenty in our biology but industrialised with those we could render from the rocks. We now even create our own elements in laboratories.
We might consider ourselves immune to the effects of evolution - as if technology has overridden the natural selective pressures of our environment - although to know for certain whether we have evolved or not, a complete map of our present genome and that of our ancestors would be needed for comparison. We have though remained stayed pretty much the same since we began recording our history in words, pictures and hypertext.
The present pressures we are applying to our environment, however, involve massive adjustments to the balance of the twenty or so elements naturally selected by nature. The effect could be to accelerate our move into a future variant on the human species.
Even if we manage to redress the imbalance will other environmental effects - emerging viruses for instance - force us down an unsuspected genetic path of change? If we carry on as we are will we pile on the pressure to the point where we begin to select ourselves out? Perhaps those with a gene that provides them with greater protection against pollutants - such as estrogenic compounds with their alleged effects on fertility - will survive the changes. The rest of us might begin to succumb to such toxic effects before we produce offspring and so drop out of the putative evolutionary scheme altogether.
The Natural Selection of the Chemical Elements, R J P Williams and J J R Frasto da Silva, Oxford University Press, Oxford, 1996.
Nature's Building Blocks: An A-Z Guide to the Elements, John Emsley, Oxford, April 2002.
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A wild recipe for hot soil
by David Bradley
The French have always had a penchant for fungi, but one day you may be more likely to find a cep cleaning up after a terrorist bomb or a nuclear accident than being served up in a wild mushroom
Edible mushrooms might not be the most obvious choice for cleaning up after a nuclear accident or the explosion of a so-called "dirty" bomb, a conventional explosive carrying radioactive material. But, French scientists reckon that a wild mushroom might soak up radioactive caesium-137 ions just as easily as it can olive oil. Caesium-137 was released in vast quantities by the explosion at the Chernobyl nuclear power station eleven years ago and could be a major contaminant from a terrorist dirty bomb.
Removing metal and radioactive contaminants from exposed land is a crucial task. Aside from the immediate threat to the environment and the health of those living on or near such land, toxic metal ions can be carried into the food chain by vegetation growing on the land. One clean-up solution, known as bioremediation, involves deliberately planting plant species that might absorb the metals from the soil and then harvesting plants for safe disposal.
When it comes to the alkali metal caesium, however, there are no plant species that thrive on soil contaminated with it. So, if not a plant, why not a fungus?
Anne-Marie Albrecht-Gary and her colleagues at the Louis Pasteur University and the University of Strasbourg think they have found the solution in the unlikely form of the tasty bay boletus, Xerocomus badius. "Fungi often exhibit a remarkable ability to accumulate a large variety of elements, ranging from the heaviest of the transition metals such as lead or mercury, to the alkali metals, including radioisotopes like caesium-137," explains Albrecht-Gary in a recent issue of Chemical Communications. But, she adds, little is known about how these fungi take up such metal ions.
She and her colleagues have studied the chemistry of the two pigments that give the inside of the bay boletus cap its bright yellow colour - norbadione A and badione A. These chemicals can act like molecular crab claws grabbing hold of metal ions in a pincer movement known as chelation. The yellow colour of the pigments provided the team with the means to test how well each latches on to metals, such as ceasium. They exploited the pigments' strong absorbtion of ultraviolet wavelengths to record a spectrum of the free pigment molecules and their spectra in the presence of caesium ions are markedly different. UV spectroscopy coupled with chemical analysis revealed that norbadione A in particular can bind to radioactive caesium very strongly. In fact, so strong is the norbadione claw that it can bind two caesium ions, whereas its weaker sibling badione A only has the strength to grip one at a time.
Albrecht-Gary and her colleagues believe that norbadione gets its strength from a so-called allosteric effect. When one caesium ion enters the claw, the molecule's chemistry changes slightly so that a second gripping position opens up to accept another caesium, working like a double claw. Badione A, on the other hand has only one possible grip.
The researchers believe that norbadione A makes the bay boletus so good at sequestering radioactive caesium ions from the soil in which it grows that it should be the bioremedial agent of choice for removing this hazardous metal from contaminated land. "Obviously, fungi can be very efficient at accumulating toxic metals and radioelements and constitute an excellent and elegant tool for soil bioremediation," says Albrecht-Gary, "However, the limitation on this very potent application is controlled growing of the mushrooms."
While norbadione A will almost certainly have a role in bioremediation, the team has dashed hopes for its medical use in removing toxic metals, such as radioactive caesium-137 cadmium and nickel, from the body. Its grip on other alkali metals, such as the essential minerals sodium and potassium is just too strong.
Of, course one problem remains: what to do with the radioactive fungi…one can hardly cook them in an omelet.