The Toxic Edge Of Drought

Corn Insect Ear Injury

Drought conditions have caused a number of problems for farmers in the US.  Among them has been a rise in plant and soil based toxins which have led to the death of dozens of cattle in the Midwest and threatened the general public with the possibility of  tainting milk and drinking water.

Concentrated nitrate

Nitrogen occurs naturally in soil and is one of the primary components of fertilizers, which are regularly applied to crops and gardens.  However, nitrate, not nitrogen, is the form that is useable by plants.  Bacteria in the soil convert  nitrogen into nitrate, allowing plants to absorb this essential nutrient.  Water plays an important role in the ability of plants to process nitrate and when water is scarce, it can lead to nitrate buildup both in plants and in the soil. After such a severe drought, some fear that once heavy rainfall occurs or when proper irrigation is re-established, these concentrations of nitrate will seep deep into the soil and may eventually reach groundwater, streams and lakes, possibly even leaching its way into our drinking water. The most notable health concern related to nitrate is methemoglobinemia—commonly referred to as “blue baby syndrome”—in which the consumed nitrate affects the body’s ability to distribute oxygen.  Fortunately, most of the population is not at risk, even if nitrate is consumed in relatively high quantities.  For infants and the elderly, however, it could be fatal. Ruminant animals and baby pigs and chickens are also susceptible to nitrate poisoning and have a higher risk of exposure both through their drinking water and in contaminated feed.

Prussic acid (cyanide)

Over 65 cattle have died from ingesting prussic acid, also known as cyanide.  Prussic acid is present in most sorghums and sudangrasses in the form of a non-toxic chemical called dhurrin.  Also present is a chemical compound called emulsion, and through any damage to the plant, such as heat stress, freezing, chewing or trampling, the two can combine to create cyanide. Both grass types thrive in higher temperatures, allowing them to grow even during the extreme heat of drought, and are often planted for summer pasture or used in feed as silage or hay.  Cattle that are allowed to range freely are susceptible when eating these forages, trampling and chewing them as they go, causing the dhurrin and emulsion to react and create the deadly poison. As a note, although these elements are always present, higher chances of cyanide formation are caused by the conditions of drought.  If the plant is stunted, soil fertility is low, or other damage is caused to the plant due to heat stress, these toxic elements will remain in the plant longer until it matures. Cattle, sheep and goats are the most susceptible to being poisoned by prussic acid.  In low doses, it can cause anxiety, labored breathing and progressive weakness.  In higher amounts, it can lead rapidly to death.


Heat stress can also increase a plant’s vulnerability to molds and fungi.  One fungus in particular, Aspergillus flavus, can be found in peanuts, pecans, grain sorghum, cottonseed and has had a notable impact on the 2012 corn crop. This fungus gets into corn kernels through heat cracks and feasts on the inside starchproducing a toxic byproduct called aflatoxin. So what’s the big deal?  If aflatoxin is consumed by livestock via their feed, it can affect their reproductive system and suppress their immune system, leaving them vulnerable to disease.   If consumed by humans, aflatoxin can act as a potent liver carcinogen.   To reduce human exposure to aflatoxin, the FDA not only tests corn but milk for its presence, as the toxin can be passed from a cow that has ingested infected corn into its milk. “It is so toxic that the Food and Drug Administration has gotten involved in trying to protect you and me and our animals from contaminated grain,” commented Dr Allen Wrather, a professor of plant sciences University of Missouri. In an interview with Dr Wrather, he stressed that the fungus itself is not toxic nor something to be alarmed about.  Rather, it is the conditions created by the drought which allow the Aspergillus flavus fungus to form the poisonous byproduct, aflatoxin.

Looking ahead

So far, the consequences for all of these toxins have been minor.  However, when considered alongside other threats to staple grains due to climate change (droughts, floods, pests, etc.), further damage to these crops could be cataclysmic down the line.  It is important to keep in mind that grains such as soy and corn are used in everything—from our processed foods, to the feed for our meat and dairy animals, to our toothpaste, to the lining in your to-go coffee cup.  With this global reliance on grain, and extreme weather predicted to become more frequent in the decades to come, significant blows to the global grain supply will ripple through every facet of our lives.

photo credit: Dr Allen Wrather

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