Scientists brought more bad news to light regarding the widely used herbicide glyphosate, better known as Roundup, in a new research paper published this month.
Researchers from the University of Turku in Finland revealed in a paper published in the journal Science of The Total Environment that manure from poultry used as fertilizer can decrease crop yields when the manure contains residues of glyphosate-based herbicides, such as Roundup. Fertilizers are meant to increase crop production, so the evidence that glyphosate residues can have the opposite effect is significant.
Poultry litter, as the manure is called, is often used as a fertilizer, including in organic agriculture, because it is considered rich in essential nutrients. Use of the poultry litter as fertilizer has been growing both in farming and in horticulture and home gardens.
While use is growing, the “possible risks associated with the accumulation of agrochemicals in poultry manure are still largely ignored,” the Finland researchers warned.
Organic farmers have been growing increasingly worried about traces of glyphosate in manure fertilizer that is allowed in organic production, but many in the industry are reluctant to publicize the issue.
Farmers spray glyphosate directly onto a number of crops grown around the world, including soybeans, corn, cotton, canola and other crops genetically engineered to withstand glyphosate treatments. They also often directly spray such crops as wheat and oats, which are not genetically engineered – shortly before harvest to dry the crops out.
Given the amount of glyphosate-based herbicides used to treat crops that are used in animal feed, as well as the amount of manure used as fertilizer, “we should definitely be aware that this kind of a risk exists,” said one of the authors of study, Anne Muola.
“Nobody seems very eager to talk too loudly about it.” Muola noted.
The heavy use of glyphosate herbicides directly onto food crops has been promoted by Monsanto – now a unit of Bayer AG – since the 1990s, and glyphosate use is so ubiquitous that residues are commonly found in food, water and even air samples.
Because there are glyphosate residues in human and animal food, detectable glyphosate levels are commonly found in human urine and animal manure.
These glyphosate residues in fertilizer are a problem for growers for many reasons, according to the Finland researchers.
“We found that poultry manure can accumulate high residues of (glyphosate-based herbicides), decrease plant growth and reproduction, and thus inhibit the growth-promoting effects of manure when applied as fertilizer,” the paper states. “These results demonstrate that the residues pass through the digestive process of birds, and more importantly, they persist in the manure fertilizer over long periods.”
The researchers said the glyphosate residues can persist in ecological systems, affecting several non-target organisms over many years.
The consequences, they said, include decreased efficiency of manure as fertilizer; long-lasting glyphosate-based herbicide contamination of agricultural cycles; “uncontrolled” glyphosate contamination of non-target areas; increased threat to “vulnerable non-target organisms,” and an increased risk of emerging resistances to glyphosate.
The researchers said more studies should be done to reveal the extent of glyphosate contamination in organic fertilizers and how that impacts sustainability.
The Finland research adds to evidence of the dangers of glyphosate residues in fertilizer, according to agricultural experts.
“The impacts of glyphosate residue that have accumulated in poultry excrements is a largely overlooked area of research,” said Rodale Institute soil scientist, Dr. Yichao Rui. “But what research does exist has shown that those residues can have a negative effect on crops, if poultry manure was used as a fertilizer. Glyphosate residues in fertilizers have been shown to have negative effects on plants, soil microbiomes, and microbes associated with plants and animals including humans through the food chain. When this contamination is unintentionally spread through fertilizer, it places a severe strain on biodiversity and ecosystem functions and services.”
Worldwide 9.4 million tons of glyphosate have been sprayed on fields – enough to spray nearly half a pound of Roundup on every cultivated acre of land in the world.
In 2015, the World Health Organization’s International Agency for Research on Cancer (IARC) classified glyphosate as “probably carcinogenic to humans” after reviewing years of published and peer-reviewed scientific studies. The team of international scientists found there was a particular association between glyphosate and non-Hodgkin lymphoma.
Tens of thousands of people in the United States suffering from non-Hodgkin lymphoma have sued Monsanto, and in three trials held to date, juries have found that the company’s glyphosate herbicides were to blame for causing the cancers.
Additionally, an assortment of animal studies released this summer indicate that glyphosate exposures impact reproductive organs and could threaten fertility, adding fresh evidence that the weed killing agent might be an endocrine disruptor. Endocrine disrupting chemicals may mimic or interfere with the body’s hormones and are linked with developmental and reproductive problems as well as brain and immune system dysfunction.