Climate change adding toxins to crops, as livestock trends create diseases

REUTERS/Lucy Nicholson
The mechanisms of toxin accumulation in key crops – think wheat, corn, soybeans, sorghum, barley, flax, millet and more – make the “poisoned chalice” the more complicated problem of this pair.

The intersection of environmental and human health is a complex and increasingly congested node. The traffic reports certainly tend toward the discouraging.

Witness last week’s fresh report from the United Nations Environmental Programme with the bland title, “Emerging Issues of Environmental Concern,” and the chilling sub-headline, “Poisoned Chalice: Toxin Accumulation in Crops in the Era of Climate Change.”

Yes, you’re reading that right. In addition to all the other challenges that farmers face from shifts in temperature, precipitation and severe weather weather events, UNEP finds that global warming is lacing their products with elevated levels of nitrates, fungal poisons and other potentially lethal compounds.

In conjunction with other human-caused pressures, climate change is also accelerating the transfer of so-called “zoonotic” diseases from animals to humans, with the Ebola and Zika viruses being but the latest headline-grabbing horrors.

Both trends happen to be afflicting the world’s poorer, tropical regions most heavily at the moment, but of course it is the central reality of global warming that it redraws the boundaries laid down by climate. And because crop toxins and viral agents are difficult to detect, they are readily diffused by trade and travel patterns that are themselves more resistant to border controls with each passing year.

The mechanisms of toxin accumulation in key crops – think wheat, corn, soybeans, sorghum, barley, flax, millet and more – make the “poisoned chalice” the more complicated problem of this pair. Here’s an especially readable interpretation of of UNEP’s findings from the Kathmandu News, among just a handful of the news accounts of the report I found over the weekend:

It is not the drought as you know it. Scientists are saying so because they have found that it is not just about scarce water. They say that when the life sustaining liquid becomes quite scarce, plants find a way of surviving the extreme condition. And that is where the good news ends. The bad news is that when plants adapt to the harsh environment, they accumulate toxins to dangerous levels that can kill livestock and can cause cancer and other serious illnesses in humans.

How about heavy rainfall after a prolonged drought? If you thought it could be a respite for us all, you are in for a surprise. A new report has shown even drought-breaking intense rains can lead to accumulation of dangerous toxins in plants. Welcome to the world of extreme weathers and toxic crops.

That is the dire message the United Nations Environment Programme (UNEP) has delivered through a report released during its second general assembly this week. Scientists who wrote the report say extreme weather conditions and rising temperatures will make 70 percent of the world’s agricultural production toxic to animals and humans across the globe.

Three groups of poisons

What toxins are we talking about? UNEP groups them into three types:

Nitrates accumulate beyond normal levels during drought because dryness slows the ability of plants to convert them into proteins; in at least 80 plant species around the world, UNEP says, this can occur at levels that result in poisoning to people and livestock, as well as economic ruin to smallholder farmers and herders.

Mycotoxins are metabolic wastes formed by the growth in crops of certain fungi, of which aflatoxin and fusarium may be among the more broadly familiar. They “can cause severe damage to the health of animals and humans at even small concentrations,” UNEP finds, and according to a 1998 study are thought to contaminated at least 25 percent of cereals worldwide.”

That number is higher now; UNEP estimates that 4.5 billion people globally are “exposed to uncontrolled and unmonitored aflatoxins” alone. In addition to lethally acute exposures, UNEP says, low-grade aflatoxin exposure is a major cause of liver cancer, accounting for perhaps a quarter of cases in Southeast Asia and a staggering 40 percent in Africa. Grains are a source of poisoning, but so are coffee, peanuts and tree nuts.

Finally there is hydrogen cyanide, aka prussic acid, which accumulates at dangerous levels after drought-stricken crops are relieved by rainfall or irrigation. (If that one sounds familiar, perhaps you are recalling that prussic acid was the base for the Zyklon B gas used in Nazi extermination camps.)

UNEP reports it can accumulate in dangerous amounts in cassava, flax, corn, sorghum, apricots, peaches, cherries, elderberries, apples and a variety of cultivated grasses.

“Deteriorating climatic conditions combine with enhanced capacities of diagnostic surveys for toxin detection to reveal that more and more global food stocks appear to be at risk of contamination,” UNEP finds.

On the brighter side, “The ability to detect these toxins is becoming less expensive and more mobile, which will help ensure that the food being produced and consumed is safe.”

Animal-to-human disease

Turning now to UNEP’s findings on animal-sourced infectious diseases, here is rather a striking passage:

Around 60 percent of all infectious diseases in humans are zoonotic, as are 75 percent of all emerging infectious diseases. On average, one new infectious disease emerges in humans every four months.

While many originate in wildlife, livestock often serve as an epidemiological bridge between wildlife and human infections. This is especially the case for intensively reared livestock, which are often genetically similar within a herd or flock, and therefore lack the genetic diversity that provides resilience. …

An example of livestock acting as a “disease bridge” is the case of bird flu or avian influenza pathogens, which first circulated in wild birds, then infected domestic poultry and from them passed to humans.

Other diseases on the list from modern times: the Ebola, Zika and West Nile viruses, along with Rift Valley fever and Middle East respiratory syndrome (MERS).  From slightly further back in time: coronavirus, more commonly known as SARS, and HIV/AIDS.

Not all of these diseases are lethal to large numbers of people, but their impact is still staggering. UNEP estimates their direct costs over the past 20 years at $100 billion, which is again the good news; “if these outbreaks had become human pandemics, the losses would have amounted to several trillion dollars.”

Climate change is not the principal culprit here; continued encroachments on wilderness for agriculture and other development are the main drivers. But so, increasingly, is something UNEP calls the “Livestock Revolution paradigm,” which is driving up meat and milk consumption across the developing world at a pace that may double production by mid-century.

Never before have so many animals been kept by so many people — and never before have so many opportunities existed for pathogens to pass from wild and domestic animals through the biophysical environment to affect people. … The result is been a worldwide increase in emerging zoonotic diseases, outbreaks of epidemic zoonoses, as well as a rise in the foodborne zoonoses globally, and a troubling persistence of neglected zoonotic diseases in poor countries.

Once again, the current problems and potential threats in the developed world remain lower than in poor places:

Global concern currently focuses on anthrax, bovine tuberculosis, brucellosis, human African trypanosomiasis, Taena solium cysticercosis (pig tapeworm), cystic echinococcosis (hydatidosis), leishmaniasis and rabies. These diseases are common where poverty, the proximity of people and domesticated animals, low resilience, and people’s reliance on livestock and wildlife converge to enable transmission.  

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The full UNEP report can be downloaded here [PDF].

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