Posted by: Green Knight | July 14, 2012

Drought, Livestock, Toxicity, and Rusty Cars

I got this e-mailed to me the other day, courtesy of a semi-local paper:

KANSAS CITY, Mo. (AP) — Missouri agriculture officials are warning that cattle grazing on some drought-stressed plants are at risk of falling ill or even dying.

One issue is nitrate poisoning. The University of Missouri Extension says nitrate poisoning poses the biggest risk in pastures that contain sorghum sudan, millet and Johnsongrass.

Animals that eat nitrate-laden plants appear to be suffocating because nitrate poisoning inhibits the ability of blood to transport oxygen.

Nitrate is a naturally occurring form of nitrogen found in the soil. Normally, little nitrate accumulates in plants because they rapidly convert nitrate to amino acids and proteins. But when conditions are dry, the roots will take up nitrate faster than the plant can convert it.

Dry conditions also can lead to potentially toxic accumulations of prussic acid in plants such as sorghum.

So, nitrates, good for plants, not so good for critters. You may recall my previous posts on selenium toxicity to livestock and wildlife (and us), and that there are certain plants that not only uptake selenium, but need it in their metabolism, but this one is new to me. Many plants, including important crop plants, have trouble “fixing” nitrogen as nitrates from the atmosphere to get what they need for their root systems, and rely on various bacteria which symbiotically do that for them in the soil. Pesticides and herbicides often kill those beneficial bacteria, thus the enormous use of NPK fertilizers (nitrogen, phosphorous, & potassium). However, I didn’t know that too much nitrate could harm grazers…as I’ve said before, everything’s toxic in the right dose. Excess agricultural nutrients like nitrates and phosphates getting into lakes and streams and causing algal blooms, which sucked up all the oxygen and caused fish kills, was one of the reasons we passed the Clean Water Act in the first place. Too much of a good thing is a bad thing, eh?

What throws me, though, is the last bit about prussic acid. James Burke should’ve done an episode of “Connections” on this one. The word “prussic” is from Prussia, the militaristic north German kingdom in the late 1800s that Otto Bismarck, the “Iron Chancellor,” functionally controlled, and used his political power to forge a unified Germany, leading to the Franco-Prussian War of 1870, which eventually led to World War One and gave us Hitler as a footnote. The Germans were always good at chemistry, and developed chemical dyes for fabrics and paper, as well as bombs, mustard gas, and other chemical warfare agents. Anything that the labs could invent that might prove useful in one way or another. That’s when science was still supposed to be free of moral considerations. Bayer (yeah, the aspirin company, from Germany) had its roots in all that. A lot of our modern organic chemicals like DDT and other pesticides also came out of warfare research.

“Prussian blue” is a dye with the formula Fe7(CN)18, and was used in paints and “blueprints.” At least the mimeograph machines when I was a kid didn’t have it, but many printing inks had toxic metals. The solvents used to keep the ink liquid were probably bad enough, but the CN in the formula equals cyanide; think CyaNide. CN, carbon and nitrogen, two totally harmless elements by themselves, but put ’em together and you’ve got something really deadly. Conversely, think about table salt, NaCl, sodium chloride. Sodium is not nearly the bad actor we used to think it was in terms of high blood pressure; the real culprit turns out to be Pb, or lead, which is still all over the shop despite the ban in residential paint in 1978. There’s still tons of it in old housing, shedding that invisible microscopic dust which is easily inhaled and messes you up. Eating paint chips is bad, but a much more secondary cause. NEVER dry-scrape old paint. But sodium, by itself as an element, is highly reactive, especially with water (don’t put any on your tongue), and chlorine is extremely toxic and tends to corrode metals, but put ’em together and you wind up with something necessary in your diet, up to a certain level. Chemistry is weird.

I first figured out what prussic acid was when I still had a car, an old rust-bucket of a Chevy that I was trying to control the rust on. I got a can of spray rust “neutralizer,” which you were supposed to apply after wire-brushing all the loose stuff  off of the trouble spots on the body. Being a safety guy, I read the label first, which most people get into trouble by not doing. One ingredient, the key one, was prussic acid, and that sounded like an old-fashioned term, and perhaps used by the manufacturer for that exact reason. There are a lot of legitimate synonyms for chemicals, along with brand names, so it can be confusing to know what you’re dealing with…getting the MSDS (Material Safety Data Sheet) from the hardware store can help you a lot. Anyhoo, I looked it up in my various reference books, notably the NIOSH Pocket Guide to Chemical Hazards, and “prussic acid” turned out to be hydrogen cyanide. HCN. Derived from Prussian blue, in fact, and one of the more popular gases used in Nazi death chambers. Hooray!

And available in auto parts stores everywhere. You may be assured that when I used that can from then on, I positioned myself upwind, and that the spray was blowing away from me. I shudder to think of people who use this stuff in enclosed garages with no ventilation. Lucky for me, I guess, that I had to park on the street.

Have a nice day.

[P.S. the symbol below is the NFPA (National Fire Protection Association) 704 placard for hazards; blue equals health or toxicity, red equals flammability, yellow equals reactivity, and white is for “special conditions” not covered by the other three. The numeric scale goes from zero to 4, from lowest to highest hazard. The symbols in the white diamond are for water-reactivity — the W with the line through it, meaning “if it’s on fire, or even if it isn’t yet, don’t spray water on it! — and OX for being an oxidizer (which is sort of a combination of flammable and reactive anyway). Nothing I’ve talked about here today, and indeed, nothing I’ve ever encountered in my decades of dealing with all this stuff, has ever actually achieved all those high numbers and characteristics at once and all by itself; I was just trying to find the worst-case label you’d ever potentially see on an emergency response. All that’s missing is the radiation symbol. And many things that exhibit really extreme physical hazards, like flammability or explosivity, may or not be toxic, but since they kill you immediately,  there’s no point or opportunity to do longterm studies. Again, when a sign says to stay away, STAY AWAY! But don’t forget that if you forgot to wear your hardhat, and a brick gets dislodged from the roof, you’ll be too dead to ask about the mineralogy or geochemistry of the brick itself, or if there was any straw in it, and it won’t matter anyway. Be safe!]



  1. P.S., a friend read this yesterday and said something like “good job on the nitrites and Prussian blue.” I had to say, NO, it’s nitrAtes, not nitrItes. Nitrites aren’t explosive, and nitrates ARE. That’s why I stress communications so much when i teach people how to deal with hazardous situations. If you’re wearing a respirator and talking on the radio, and someone on the other end hears you wrong, things could go kablooey really fast. To quote the title of an old soap opera, you only have “One Life to Live.”.

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