Every one in a fortunately rare
while, Mother Nature dishes up a very unpleasant surprise. We also get reminded that Mother Nature has
been happily handling cyanide forever with some success. In this case the right combination of
stressors triggered a cyanide rich meal for the cattle.
A bit of research may police up
plausible warnings or even a plausible test rig. We sort of need to know even when the risk is
only border line anyway. The problem likely
goes away in time when it does arise, thus a test prevents another source of
stress.
In the event the press got
excited because it looked to be an opportunity to bash GM plants again.
The Curious Case of the Poisoned Cows
By Deborah
Blum
June 29, 2012
On a bright morning in early June, a Texas rancher named Jerry Abel turned his
small herd of cattle out to graze. The 18 cows moved hungrily into that field
of fresh grass. Within a few hours, only three were still alive.
Abel’s 80 acre ranch sits just a little east of Austin and the story was strange enough that
on Sunday a local CBS affiliate picked it up. “There was nothing you could do,”
Abel told
KEYE about his desperate efforts to save the animals. “Obviously, they
were dying.”
The television reporter apparently saw the evil hand of science at work
in the episode, at least that was definitely the message in the story: “Genetically
modified grass linked to cattle deaths.“ Alternatively, she just didn’t
do her homework because the grass in question – Tifton 85 - is not a
GM product. It’s a decades old hybrid grass developed by Georgia agricultural scientists as
a high-protein, easily digestible forage.
The CBS story was immediately circulated – and by circulated, I mean
embraced – by anti-GM activists and bloggers. I wrote
a summary of this for the Knight Science Journalism Tracker earlier
this week which detailed both the activist enthusiasm for the story (one
suggested that GM grass was practically producing chemical warfare agents) and
the rapid corrective response from science writers who knew what “hybrid” actually
meant. The you-got-this-wrong message was so strong that CBS News corrected
the story within a day.
But my point here is not to review the media issue but to take a look
at the Sherlockian mystery of how a pasture full of a well-known hybrid grass
could suddenly turn so murderous. And I’ll give away part of the solution by
reminding you of something we tend to forget in our obsession with the
risks of synthetic chemistry and genetic engineering. What the Texas cow story reminds
us – or should – is that naturally occurring chemistry can be just as wicked as
anything we dream up in a laboratory.
There’s no debate over the poison that killed Mr. Abel’s cows.
Hydrogen cyanide was found both in the cow’s bodies and in the grass itself.
The veterinarian who autopsied the animals, called
it prussic acid poisoning. Prussic acid is an old-time term for
hydrogen cyanide (derived from hydrocyanic acid), dating back to some 18th
century chemistry experiments in which a deep blue pigment used by
artists, called Prussian
Blue , was mixed with acid to generate the poison.
The foundation of any cyanide is a a cyano group – basically a carbon
atom tripled bonded to a nitrogen atom (with the chemical symbol CN). Cyanides
are natural joiners, attaching to other chemicals with enthusiasm. Thus we have
the gases hydrogen cyanide (HCN) and cyanogen chloride (CNCl) and the salts –
sodium cyanide (NaCN), potassium cyanide (KCN). All are acutely
poisonous. And while I earlier mocked the anti-GM activist comparing Texas grass to chemical
weaponry, both hydrogen cyanide and cyanogen chloride do have military
designations. The military symbol for hydrogen cyanide is AK.
But don’t let that fool you into thinking that cyanides are a human
invention. They aren’t. We just capitalized on an invention of nature itself,
a chemistry shared by numerous plant species including some
grasses. Why? Most scientists believe that plants developed this
chemistry as a way of fending off predators, from insects to grazers. The
plants store cyanides in an inactive form but they can release them under
threat or stress.
The stored forms of cyanide in plants are called cyanogenic glycosides.
Basically this tells us that the cyanide is bound to – neatly locked up by –
sugars in the plant. Under stress, though, the cyanide-sugar bond can break and
the poison can be released. How many plant species hold this potential?Thousands. After
the Texas
cattle story appeared, the scientist and blogger Mary Mangan sent
me a link to a 1998 article in the journal Phytochemistry titled “Why Are So Many Food Plants
Cyanogenic”?
The paper’s author, David A. Jones, points out that “There are now sufficient
examples of plant defense by cyanogenesis for us to conclude that cyanogenesis
is an important system of chemical defense in plants.” He then reviews an
astonishing variety of food plants that contain these precursor poisons,
including wheat, barley, oats, rye, French beans, kidney beans, lima beans,
apples, peaches, plums, apricots, cherries, almonds, Macadamia nuts, quince,
papaya, passion fruit, bamboo shoots, cassava root, taro root and more.
As Jones notes, in most cases we are eating plants in which the
cyanides remain locked up by the surrounding sugars. Or they are found in parts
of the fruit, say, that we normally don’t eat – the seeds of the apple, the pit
of the peach. And we usually eat them in a small enough amount (dose) and at a gradual
enough rate that our own metabolic enzymes can break them down into a
relatively harmless state. I say relatively because there are some
instances of harm from what Jones calls “chronic cyanide poisoning of humans”,
but these tend to occur in high risk groups. People with sickle cell diseases,
tobacco smokers, people with Leber’s
disease (an inherited degeneration of the optic nerve) seems less able
to detoxify cyanogenic compounds. As one example of this, Jones cites a number
of Leber’s patients who went blind due to the cyanogens found in apple cider.
None of this, you’ve probably noted, involves people or animals
suddenly dropping dead of cyanide poisoning. Most of that of course, is because
we’re still talking about consumption of those sugar-bound poison molecules.
But what if the plant is an unhappy plant? What if it’s suffering from
sustained, damaging stress? And what if, under that stress, the glycosides
unravel and release pure hydrogen cyanide?
As we all know, Texas
is in the midst of a sustained and destructive drought. And as it turns out,
there’s quite a bit of research showing that forage grasses can become
surprisingly poisonous when they are stressed by heat and drought. To that end,
I refer you to this article from the University
of Wyoming titled, “Managing Forages to
Minimize Prussic Acid Poisoning.” Or “Livestock and Prussic Acid
Poisoning” from Ohio
State University .
Or “Preventing
Prussic Acid Poisoning of Livestock” from Oregon State
University . And as
it also turns out, the Tifton 85 grass in Mr. Abel’s field is a hybrid
of Bermuda grass and star grass. And star grass is one
of those cyanogenic plant species we’ve just been discussing.
All of which suggests that Mr Abel’s cows were caught in a lethal
interaction between some very old and very well known plant chemistry and an
entrenched period of hot, dry weather. As you’ve noticed, this doesn’t
solve for the entire mystery. Why this field and not other Texas fields planted with Tifton 85? One
possibility is suggested by an investigation
by Natural News, which points out that heavy use of nitrogen fertilizers
can influence the cyanogenic process. Natural News, of course, is firmly in the
anti-GM camp but even it concluded that “there appears to be no GMO, no secret
experiments, no conspiracy.”
There’s a hint of disappointment in that line. But there shouldn’t be.
Because this piece of scientific detective work leads us to a point that – as I
said earlier – we too often forget: that we live in a chemical word, amazing,
complicated, ingenious, and occasionally wonderfully, startlingly, and
terrifyingly lethal.
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