Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Archive for the ‘environment’ Category

The environmental footprints of coal and uranium mining.

with 10 comments

Here’s something worth thinking about.

This is a coal mine. Specifically, it’s the Blair Athol coal mine in central Queensland, Australia, but there’s no special reason why I chose this specific example of a coal mine. The mine produces 12 megatonnes of coal per year. (This is just a satellite image taken from Google Maps, which anybody can of course easily access.)

Coal has a thermal energy content of about 25 MJ/kg, and therefore 12 megatonnes of coal corresponds to a primary energy content of about 2.9 x 1017 J.

This is the Ranger uranium mine, near Jabiru in the Northern Territory of Australia. Again, nothing special about this specific uranium mine, it’s just an example.
All these satellite images are at a consistent scale factor, or zoom level/resolution.

In 2007-2008, Ranger produced 5273 tonnes of U3O8.

A conventional, relatively inefficient low-enriched uranium fuelled LWR with a thermal (primary energy) power output of about 3 GW requires approximately 200 tonnes of U3O8 to be mined to fuel it for one year, assuming that newly mined uranium is used for all its fuel.

Therefore, the annual uranium output from Ranger corresponds to about 2.5 x 1018 J of primary energy, or about 8.6 times the primary energy content supplied by the coal mine.

That is, that one uranium mine supplies the same amount of energy content as nine of the coal mines – one seemingly quite small uranium mine, which is about a third of the size of the coal mine, supplies the same amount of primary energy content as this. (I won’t embed that image in the post, since it will probably completely destroy the formatting of the page.)


Written by Luke Weston

January 9, 2009 at 7:24 am

“What comes out of the stack is, basically, a moist air”

with 4 comments

“Moist air” !? How stupid do they actually think people are?

No, unfortunately – I’m pretty sure this one isn’t satirical. I wonder how much mercury will end up in those fish?

If the embedded video player doesn’t work for you whatever reason, here’s the direct YouTube link.

Written by Luke Weston

May 1, 2008 at 4:30 pm

Bioconcentration and biomagnification of radionuclides of biochemically-significant elements.

with 5 comments

 Anti-nuclear-energy activists often talk about the potential for biomagnification of radioactive nuclides in the environment as the consequence of any, even extremely dilute, releases of such radionuclides into the environment.

Consider the following claims, typical of such views, for example:

“Tritium is also more dangerous when it becomes organically bound in molecules of food. As such it is incorporated into molecules, including DNA within bodily cells. Chronic exposure to contaminated food causes 10% of the tritium to become organically bound within the body where it has a biological half-life of 21 to 550 days meaning that it can reside in the body from one to twenty-five years.”

“When tritium is released to the environment, it is taken up by plants and trees, partially incorporating into the ecosystem. Trees constantly transpire water vapor into the air; it has been found that higher concentrations of tritium occur at night at breathing height in a forest that has incorporated tritium from a nearby reactor.”

(Extracts from Nuclear Power is Not the Answer) 

So, does bioconcentration of tritium in the food chain occur?

Bioconcentration or biomagnification of tritium in the form of tritiated water in biological systems does not occur at all, although it can occur with some other radionuclides. This is due, in part, to the relatively small biological half-life for water in biological systems, and the large concentration of light water in the environment, which results in massive isotopic dilution of tritium entering the ecosphere. Tritium is simply hydrogen, and your body cannot tell one hydrogen atom from the next – whilst large volumes of water are constantly being taken into the body, and passed out of the body, the total amount of hydrogen within ones body remains essentially constant, as is also the case for the various other chemical elements which make up the human body.

Biomagnification is the buildup of certain chemical pollutants in the bodies of organisms at higher trophic levels of food webs – the bioaccumulation of a substance up the food chain by transfer of residues of the substance in smaller organisms that are food for larger organisms in the food web. It generally refers to the sequence of processes that results in higher concentrations in organisms at a higher trophic level – further “up the food chain”. Organisms at lower trophic levels accumulate small amounts. Organisms at the next higher level eat many of these lower-level organisms and hence accumulate larger amounts. These processes result in an organism having higher concentrations of a substance than is present in the organisms prey or food. Biomagnification can result in higher concentrations of the substance than would be expected if water were the only exposure mechanism. Accumulation of a substance only through contact with water is known as bioconcentration.

Bioaccumulation is a general term for the accumulation of such substances in an organism or part of an organism. The process of bioaccumulation involves the biological sequestering of substances that enter the organism through respiration, food intake and/or other routes of absorbtion of the substance. Such sequestering results in the organism having a higher concentration of the substance than the concentration in the organisms surrounding environment. The level at which a given substance is bioaccumulated depends on the rate of uptake, the route of uptake, how quickly the substance is eliminated from the organism, transformation of the substance by metabolic processes, the lipid (fat) content of the organism, the hydrophobicity of the substance, environmental factors, and other biological and physical factors. As a general rule the more hydrophobic a substance is the more likely it is to bioaccumulate in organisms, such as fish. Increasing hydrophobicity (lipophilicity) leads to an increasing propensity towards bioaccumulation.

A related term is bioconcentration. Bioconcentration is a process that results in an organism having a higher concentration of a substance than is in its surrounding environmental media, such as stream water. Bioconcentration differs from bioaccumulation because it refers only to the uptake of substances into the organism from water alone. Bioaccumlation is the more general term because it includes all means of uptake into the organism.

Biomagnification, or bioamplification, occurs within a trophic level, and is the increase in concentration of a substance in an organisms tissues due to uptake from food and sediments in an aquatic milieu, wheras bioconcentration is defined as occurring when uptake from the environment is greater than the rate of excretion. Where bioaccumulation refers to how pollutants enter a food chain; biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next, up the “food chain.” Whilst bioaccumulation refers to an increase in concentration of a pollutant from the environment to the first organism in a food chain, biomagnification refers to an increase in concentration of a pollutant from one link in the food chain to another.
We are traditionally concerned about these phenomena because together they mean that even small concentrations of toxic substances in the environment can find their way into organisms in high enough dosages to cause problems. In order for biomagnification to occur, the pollutant must be long lived, fat-soluble, mobile, and biologically active – i.e. toxic. If a pollutant is short-lived, it will be broken down before it can become dangerous. If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms. If the pollutant is soluble in water it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time. Lipid soluble (lipophilic) substances cannot be excreted in urine, an aqueous solution, and so accumulate in fatty tissues of an organism if the organism lacks enzymes to degrade them. When eaten by another organism, fats are absorbed in the gut, carrying the substance, which then accumulates in the fats of the predator. Since at each trophic level of the food chain there is an energy loss, a predator must consume lots of prey, and therefore consumes significantly larger amounts of any biomagnifying lipophilic substance consumed by the prey organism.

There are two main groups of toxic substances that that are subject to biomagnification – toxic metals and persistent halogenated organic compounds. Both are lipophilic and not easily degraded. Novel organic substances are not easily degraded because organisms lack previous exposure and have thus not evolved specific detoxification and excretion mechanisms, as there has been no selection pressure from them. These substances are consequently known as persistent organic pollutants, and include the synthetic organic chlorine compounds which are today well-known for their potential for biomagnification and environmental harm, such as the insecticide DDT.

Heavy metals are chemically stable because they are chemical elements, and therefore cannot be destroyed or converted into a non-toxic form. (Except for the case of a radioactive metal, which will change into a differerent chemical element when it undergoes radioactive decay.) Organisms, particularly those subject to naturally high levels of exposure to metals, have mechanisms to sequester and excrete metals. Problems arise when organisms are exposed to higher concentrations than usual, which they cannot excrete rapidly enough to prevent damage. These metals are transferred in an organic form.

A classic example of a toxic heavy metal is mercury, which forms organic species such as methylmercury, which is lipid soluble, and can easily biomagnify in environmental systems. Other toxic transition metals – the so-called “heavy metals” – can be subject to biomagnification to some degree, too – for example, the toxic metal cadmium. Since biochemical behavior is independent of what the isotopic composition of the metal is, a radionuclide, such as the low-yield fission product \mathrm{^{113m}Cd}, perhaps, is subject to a potential for biomagnification just like any other cadmium. For example, though mercury is only present in small amounts in seawater, it is absorbed by algae, generally as methylmercury. It is efficiently absorbed, but only very slowly excreted by organisms. Bioaccumulation and biomagnification result in buildup in the adipose tissue of successive trophic levels: zooplankton, small nekton, larger fish etc. Anything which eats these fish also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as swordfish and sharks or birds like osprey and eagles have higher concentrations of mercury in their tissue than could be accounted for by direct exposure alone. For example, herring contains mercury at approximately 0.01 ppm and shark contains mercury at greater than 1 ppm.

Now, let’s talk about radionuclides. radioactive nuclides such as, say, hydrogen-3, carbon-14, iodine-131 or strontium-90, for example, can certainly be uptaken by living organisms – including, but not limited to, humans. Tritium (hydrogen-3) is almost always present in the environment in the form of water – and, of course, every living thing uptakes water from its environment, so, if there is \mathrm{^{3}H} present in the water – keep in mind that all water has some naturally occurring \mathrm{^{3}H} in it – then \mathrm{^{3}H} will be absorbed by the organism. Now, remember – it is just hydrogen.

The biochemistry of cells does not care in the slightest what nuclide a particular atom of hydrogen or a particular element is – it is only concerned with the chemistry of the material. Therefore, the \mathrm{^{3}H} will be used by the cells of the organism, and incorporated into tissues and biomolecules along with every other hydrogen atom that the organism has uptaken. Since an atom of tritium is just another hydrogen atom, of course it is exchanged into and incorporated into some hydrogen-containing biomolecules – in other words, just about any organic molecule found in a biological system. However, water is constantly being excreted from living systems as well as constantly being uptaken – a cell of Escherichia coli contains 70% water by mass, a human body 60-70%, plant tissue up to 90% and the body of an adult jellyfish is made up of 94 to 98% water. Now, the proportion of water in an organism such as these is constant – except for a small difference due to the growth of the organism, the rate of water uptake into an organism is equal to the rate of water excretion, and whilst hydrogen – which could be \mathrm{^{1}H}, \mathrm{^{2}H} or \mathrm{^{3}H}, it doesn’t matter – is constantly being moved between water molecules and more complex biomolecules, and it is constantly being excreted – both in the form of water and in the form of more complex biomolecules.

However, some tritium taken up into the body could be incorporated into a biomolecule in the tissues of the body, and it could remain there for some time – but as more stable hydrogen is constantly being exchanged through the body in large quantities, the concentration of tritium within the body from any given intake will decay exponentially, just as the metabolism and excretion of, say, a drug taken into the body follows an exponential decay law – hence, we speak of the biological half-life.

The overall amount of hydrogen per unit mass of a living organism is essentially constant. If there is a constant environmental source of a radionuclide such as tritium – such as the natural cosmogenic formation of tritium – then the overall amount of tritium per unit mass of a living organism is essentially constant.

Exactly the same argument applies to radionuclides of other biologically active elements – like, say, carbon-14. \mathrm{^{14}C} is constantly uptaken from the atmosphere by plants in the form of \mathrm{^{14}CO_{2}}, and incorporated into the organic biomolecules within the tissues of the plant as the plant grows – and when an animal eats the plant, the \mathrm{^{14}C}-containing biomolecules are metabolised by the animal. As with hydrogen nuclides, the \mathrm{^{14}C} is constantly being turned over between living systems and the ecosphere, as organic compounds are excreted by the animals – for example in the exhalation of \mathrm{^{14}CO_{2}}. Again, the overall concentration of \mathrm{^{14}C} within the tissues of a living system is held constant – this is how carbon-14 dating works! If the concentration of \mathrm{^{14}C} within a living organism wasn’t constant, then obviously \mathrm{^{14}C}-dating of once-living materials would be impossible.

The same arguments apply to, say, strontium, or iodine – whilst a radionuclide such as strontium-90 certainly can be uptaken into the human (or animal) body, and can be used in osteogenesis and incorporated into bone because of the chemical similarity between \mathrm{Sr^{2+}} and \mathrm{Ca^{2+}}, the overall concentration of calcium – calcium and strontium combined, for that matter – within the body is maintained at a certain static level. When iodine – some of which could be contaminated with, say, radioactive iodine-131 – is uptaken by the body, iodide ions are used by the thyroid gland in the biosynthesis of the iodine-containing thyroid hormones, thyroxine and triiodothyronine. But, of course, the concentration of thyroxine and triiodothyronine in the blood is kept around a fairly homeostatic value – whilst some iodine is essential for the biosynthesis of these hormones and is thus essential for health, it does not accumulate arbitrarily in the body, either in the form of the iodine-containing hormones or as free iodide ion.

Obviously we know that such chemical elements – radionuclides or not – are uptaken extensively by biological systems; but that is not the same thing as biomagnification – do they bioaccumulate or biomagnify?

Clearly, they do not.
It has in fact been determined empirically in Perch Lake in Canada that there is a progressive decline in the concentration of cobalt-60 and strontium-90 as they are transferred to higher trophic levels. In other words, predators, such as carnivorous fish, have lower concentrations of cobalt-60 and strontium-90 per unit body weight than do forage fish, insects and plants, as a result of biological discrimination against uptake of these elements of limited biochemical usefulness. It is now generally agreed that the same principle is valid for most other radionuclides, with a few exceptions, such as tritium, soluble potassium-40 (which occurs naturally, not as a result of anthropogenic nuclear technology), and caesium-137, which is a chemical analog of potassium, which are incorporated without biodiscrimination into all living organisms. Most radionuclides are not subject to biomagnification up the food chain, thus differing them from organic pollutants such as DDT. This is of significant importance in the assessment of radioactive  releases into the environment.

Editor’s note: As you may note, I’ve just discovered WordPress’s built-in LaTeX engine. Unfortunately, it looks a little bit awkward in the above post, as you can see, with the TeX-formatted text much bigger than the surrounding text. I’ll have to see if there’s a way around that in future.

Nuclear Madness: Chapter 1

with 10 comments

Yes, I’m referring to the book.

 “…we can no longer afford to entrust our lives, and the lives and health of future generations, to politicians, bureaucrats, “experts”, or scientific specialists, because all too often their objectivity is compromised.”

Oh dear oh dear. In other words, any scientist or engineer, physician or physicist, who potentially disagrees with us, must clearly be a shill.

But it doesn’t really matter, fundamentally. Ultimately, if a physicist or chemist says this or that, ultimately, what they say is tested against the physical characteristics of reality. What scientists say, by rights, doesn’t matter. What physical reality does is what matters. Nature can’t be paid off by the big scary corporations and lobby groups.

 “It (nuclear energy) is also obviously extremely unsafe, as opposed to the fallacious claims made by the nuclear industry…”

The empirical observation is that it is safe. He-says-she-says doesn’t matter.

“The Oak Ridge National Laboratory in Tennessee exposed nearly 500 patients with leukemia and other cancers to exceptionally high levels of radiation from radioactive caesium and cobalt, including a six-year-old boy.”

The infamous human radioactivity experiments are potentially a great topic of discussion for the people that want to convince the public that human applications of radioactivity are intrinsically evil. I’m not quite sure what relevance the infamous and controversial research has to nuclear energy, but reading the above passage, one thing immediately stands out.

Thousands of patients with cancers are exposed to exceptionally high doses of radiation, from radionuclides of Caesium and cobalt, in hospitals every day, even today. And it saves their lives.

  “…the long-term medical consequences of radiation were just beginning to appear, in the form of an increased rate of leukemia among Japanese atomic bomb survivors.”

These are the medical consequences of very high doses of whole-body ionizing radiation exposure. That these grave medical consequences of very large doses of ionizing radiation exist, and what they are, has never, ever, been in any dispute. Very high doses of ionizing radiation kill people.

“Nonbiodegradable, and some virtually potent forever, these toxic nuclear materials…”

Radionuclides are non-biodegradable! My god.

If one synthesises a biodegradable polymer, such as a lactide-derived polyester, and labels it with say Tritium or Carbon-14, the radioactive polymer is still biodegradable.

All radionuclides intrinsically, inevitably, decay over time. This is one of the most intrinsic and fundamental aspects of the phenomenon of radioactivity.

Polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are strongly mutagenic, and correspondingly carcinogenic and teratogenic, and exposure to these compounds in the environment has the potential to cause increased incidences of cancer, decades into the future, and leave future generations with legacies of genetic disease, birth defects and so forth, as a result of mutation of genes reproductive cells in generations exposed to these pollutants.

This is the legacy we leave to future generations with the continued use, and expanded use, of dangerous fossil fuels.

These persistent organic pollutants in dangerous fossil fuel waste are not biodegradable, and their nuclei are for the most part, stable. They do not break down over time, or decay. At all.

“Each 1 GW nuclear (power) reactor contains as much long-lived radioactive material (“fallout”) as would be produced by 1000 Hiroshima-sized bombs.”

Radioactive material is not “fallout” until is is dispersed in the atmosphere in the form of dispersed dust, volatile and particulate contamination. Arguably, the Chernobyl disaster created radioactive “fallout” contamination, kind of analogous to that produced by a nuclear weapon.

But in practice, what circumstances are required for such dispersion to be created with any other nuclear reactor?

“A “meltdown”, in which the fissioning nuclear fuel overheats and melts, penetrating the steel and concrete structures that encase it, could release a reactor’s radioactive contents into the atmosphere…”

Can a “meltdown” destroy the steel reactor vessel of a nuclear reactor? Theory shows it’s extremely doubtful, and experience, at Three Mile Island, says no. Even if the pressure vessel is destroyed, could the massive reinforced concrete containment building be destroyed by hot, partially molten, fuel? For all practical intents and purposes, such an idea is regarded as impossible.

 “One need not be a scientist or nuclear engineer to take part in this important debate; in fact, an over-specialised approach tends to confuse the issue. The basic questions involved ultimately go beyond the technical problems related to reactor safety and radioactive waste management.”

What? In other words, is Caldicott trying to tell us that the science and engineering does not matter? These are the most fundamental aspects of the debate. On a foundation of scientific and technological fact, the complex political and social debate over nuclear technology can proceed in a sensible, informed manner.

“How can we ensure the longevity of the social institutions responsible for perpetuating that isolation?” (the isolation of radioactive waste from the environment over the long term.)  “And what moral right do we have to burden our progeny with this poisonous legacy…

Social institutions do not perpetuate the longevity of that isolation. Half a kilometer of solid rock perpetuates it. We know from history, from the nuclear fission waste under the rock at Oklo, and from, say, the great Pyramids, that these great structures of rock will carry our legacy over the time frames required.

Permanent geological repositories,  such as that under construction by Sweden’s SKB, deal with the radioactive waste permanantly, and once it’s sealed, it’s dealt with, safe forever. These repositories require no monitoring or maintainence by future generations.

Well, that’s Chapter 1, and the Introduction, covered.

Written by Luke Weston

August 8, 2007 at 1:29 am