Following cadmium flows in grains and other plants by isotopic fractionation.
Cadmium is highly toxic element that occurs naturally in some soils, but has been increasingly contaminating agricultural fields since the element has been mined extensively in order to serve the electronics industry.
It is known that the element is taken up by plants since it is mimetic for the elemental essential nutriet zinc, zinc being present in the active sites of many important metalloenzymes essential to life. When coordinated with cadmium rather than zinc, the enzymes no longer function, and this is important to the mechanism by which their toxicity is observed. (The third cogener of zinc is mercury, and the mechanism of its toxicity is generally the same: Both cadmium and mercury are powerful neurotoxins, which may account for the unfathomable popularity of Donald Trump.)
An interesting paper I came across on the subject in the current (as of this writing, 9/10/16) issue of Environmental Science and Technology is here: Cadmium Isotope Fractionation in Soil–Wheat Systems (Matthais Wiggenhauser et al, Environ. Sci. Technol., 2016, 50 (17), pp 9223–9231)
Here is a graphic from the paper:
It is important to note that the percentages here do not refer to enrichment of total cadmium in the various plant parts, but rather in the ratio between two stable isotopes of the element, 114Cd and 110Cd, with the former being enriched.
Isotope effects such are these are related to the kinetics of reactions, which vary (slightly) with the mass of the reactants. These effects are well known for the hydrogen isotopes protium, deuterium and tritium, but, as the paper points out in the text, have only in recent times been accessible to study owing to developments in inductively coupled plasma mass spectrometry (ICP-MS). For the analytical chemist, details may be found in the supplementary information of the paper although the particular make and model of the ICP/MS is not noted.
The lighter the isotope, in general, the faster the reaction. In the present case, it was found that the cadmium that makes its way to the wheat seeds, the grain we eat, is enriched in heavier isotopes meaning that the reactions in the stems and roots remove some cadmium before it gets to our mouths and, ultimately our brains where it causes diseases like Trumpism and Greenpeacism and other neurological deficiencies. This is actually good news, since it means that some of the cadmium is sequestered in these inedible parts of grain, although in the case of straw, it may show up in animals that some people eat, in particular, cows.
Despite this marginally good news, it is clear that many food supplies are in fact contaminated with cadmium, especially in China, where electronic recycling, as well as mining and manufacture of semiconductors solar cell are practiced under largely uncontrolled conditions. It is reported that in Southern China, up to 70% of the grains purchased in local markets had cadmium levels exceeding government set limits: F ood supply and food safety issues in China (Sun et al Lancet 2013; 381: 2044–53) About 1/6 of the world supply of cadmium is mined in China; substantial quantities are mined in the United States and isolated from various zinc ores.
We hear a lot of hand waving about how solar prices are dropping dramatically, and Chinese manufacture of solar cells is a big part of the reason, because in China, despite having declared itself a "people's state" environmental regulations either do not exist or if they do, are poorly enforced. In China it is cheaper to dump cadmium containing wastes and avoid the purchase of expensive devices to prevent the escape of these contaminants, as well as other contaminants like tetrachlorosilicon, and yes solar prices are dropping. Whoopeee.
(The big lie about "dropping solar prices" is that any system that requires redundancy is not cheaper; it is in fact, more expensive than a system that operates continuously. Also from both an economic and environmental standpoint, the lifetime of a device matters.)
The solar industry has almost no effect whatsoever on the most exigent environmental crisis of our times, climate change. After the world's population dropped a trillion bucks on this adventure in wishful thinking and poor critical thinking ability, the result is that the rate of accumulation of the dangerous fossil fuel waste carbon dioxide in the planetary atmosphere has pretty much tripled since the big mouthed advocates of this scheme - I'm talking specifically about corporate window dresser Amory Lovins specifically, although one could point to similar assholes like his one time acolyte Joe Romm - began telling us all that solar and wind would save us.
They haven't, they aren't, and they won't.
The import of cadmium laced solar cells into the United States from China will probably have little immediate toxicological effect - although I'm not sure the issue has been studied - but in twenty or thirty years all the solar cells on this planet, as well as the inverters and other electronic junk associated with them, will become another component of electronic waste, already an intractable problem. The toxicological effects thus will fall on future generations. By doing nothing but failing to check our 1970's assumptions, the members of this generation, my generation, have showed their contempt for all future generations in thousands of ways, and piling up this solar junk is only the tip of the overheated iceberg.
By the way, cadmium is one of the "critical elements" that are likely to be depleted in the lifetime of today's infants. Here is a periodic table from one source on this increasingly discussed issue in Engineering, Materials Environmental Sciences: The importance of elemental sustainability and critical element recovery (Hunt et al, Green Chem., 2015,17, 1949-1950
It is somewhat amusing to note that five of the elements that have been touted as "solar breakthroughs" in the last twenty or thirty years of useless cheering, five of them are on the list of immediately endangered elements, those expected to run out in the next fifty years, the aforementioned cadmium, as well as gallium, germanium, indium and arsenic. (Indium may well run out first, not because of useless solar cells, but because of touch screen phones and other screens.) Two others, selenium and tellurium, both toxic elements, will run out in the next century.
So much for the hope that the solar industry, where "PRICES ARE DROPPING!!!!!!!!!" will end up producing all that much more than the less than the 2 exajoules it produces right now out of the 570 exajoules of energy that humanity now consumes each year.
Enjoy the rest of the weekend.
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