Is organic food really better for your health? When they launched their experiment in 2017, researchers at the Chizé Biological Studies Center (University of La Rochelle) and the Biogéosciences laboratory (University of Burgundy) were not trying to answer a public health question but rather an environmental one. “We wanted to find out how contamination of the environment by low doses of pesticide mixtures – those found in agricultural areas – could affect the survival of farmland birds like the grey partridge,” explained Jérôme Moreau, a biologist and ecologist from the University of La Rochelle. “It was difficult to find an experimental protocol mimicking these living conditions to compare them with a situation where the animals have little or no exposure, so we chose to alter the birds’ food.”
For several months, the researchers raised two groups of grey partridges. The first was fed on organically grown wheat and corn, while the other was given the same grain from conventional farming. The goal was to observe the impact of traces of synthetic pesticides – banned in organic farming – present in the birds’ diet. “Some colleagues told us we wouldn’t see any effect. On the contrary, the results were striking and took us by surprise,” said Moreau.
In just a few weeks of experimentation, the immune systems of “conventional partridges” became unbalanced compared with those of “organic partridges,” their red blood cell count fell, and the number of intestinal parasites increased. These results, which were published in Environmental Pollution in 2021, also showed that conventional females lay smaller eggs with thinner shells. They also built up more body fat and became heavier than “organic” ones. As for the males, their plumage became less colorful. According to the researchers, these sex-modulated effects could be linked to some pesticides’ endocrine-disrupting properties.
Impact on reproduction
Their latest observations, published in 2023, even showed that feeding these birds a conventional diet reduced their ability to fly and lowered their vigilance. “Flight zone – in other words, the distance at which a partridge will flee if an intruder gets near – was around half that of conventionally-fed birds,” said Moreau. This could indicate likely repercussions on the birds’ central nervous system.
These findings were in line with other, much older animal studies. In an article published in 2009, Alberta Velimirov (FiBL, Vienna) and his co-authors compiled this now-overlooked research. As early as the 1920s, scientists studied whether synthetic fertilizers could affect crop quality – and, consequently, those who eat them – compared to natural fertilizers. Between 1926 and 1987, a dozen studies on rats, rabbits, chickens and cattle were published, most showing adverse effects on reproduction, survival, litter size, etc. In 1965, two German researchers observed that sperm from bulls fed hay grown without synthetic fertilizers had better motility. What could be the causes? One of the explanations now offered is the presence of heavy metals like cadmium in chemical phosphate fertilizers.
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