Mineral Fertilizers Linked to Toxic Metal Accumulation in Wheat, new Research Finds
A groundbreaking study published in Environment International reveals that mineral fertilizers, rather than the soil itself, are the primary source of toxic metals like cadmium found in wheat grains. The findings, stemming from a collaborative effort between the Helmholtz Center for Environmental Research (UFZ) and Duke University, suggest a shift towards combined fertilization strategies could simultaneously reduce toxicity and boost nutritional value.
Why did this research happen? A long-standing debate existed regarding the source of toxic metals in crops – whether they came from the soil or fertilizers. Scientists aimed to definitively answer this question to inform agricultural practices and improve food safety.
A long-standing question in agricultural science has been the origin of toxic metals absorbed by crops. Researchers previously debated whether these metals originated from the soil or were introduced through fertilizers. This new research, utilizing a novel isotope tracing technique, definitively points to the latter.
Who was involved? The research was a collaboration between the Helmholtz Center for Environmental Research (UFZ) in Germany and Duke University in the United States. It involved senior researchers,doctoral students,and scientists specializing in environmental science and agricultural chemistry.
The investigation centered around a unique, long-term agricultural experiment established in 1902 at the UFZ Bad Lauchstädt research station. this “static fertilization experiment” features plots that have remained unfertilized for over 120 years, alongside others treated exclusively with mineral fertilizers, organic fertilizers like manure, or a combination of both. “The long duration of this experiment, and the meticulous record-keeping, provided an unparalleled opportunity to unravel this complex issue,” explained a senior researcher involved in the study.
Over the past two decades, scientists analyzed soil samples, wheat grains, and the fertilizers themselves, employing the strontium isotope signature method. This technique hinges on the fact that strontium, a chemical element, exists in different isotopic forms – Sr and Sr – with varying ratios unique to each soil type. by comparing the strontium isotope ratios in the wheat grains to those in the soil and fertilizer, researchers could pinpoint the source of the metal uptake. “It’s essentially a fingerprinting process,” stated a doctoral student at Duke University. “If the ratio in the grain matches the fertilizer, we know the metal came from there.” Because plants absorb strontium and cadmium through similar pathways, the findings regarding strontium isotopes directly inform our understanding of cadmium accumulation.
What did they find? The study conclusively demonstrated that mineral fertilizers are the primary source of toxic metals, specifically cadmium, in wheat grains. Wheat grown with mineral fertilizers had significantly higher metal content than those grown with organic fertilizers.
The results were conclusive: the majority of toxic metals in the examined wheat grains originated from the applied mineral fertilizers, not the underlying soil. Furthermore,wheat grown with mineral fertilizers exhibited significantly higher metal content compared to those grown with organic fertilizers. Researchers caution that these findings are notably relevant in regions with fertile black earth soils, and the effects could be even more pronounced in sandy or acidic soils. The study also highlighted that long-term mineral fertilization contributes to soil acidification, emphasizing the importance of pH stabilization techniques like liming.
However, not all metals in mineral fertilizers are detrimental. Zinc, a crucial trace element for human nutrition, is one example. the research team discovered a promising synergy: combining mineral and organic fertilizers not only reduced cadmium uptake but also increased zinc content in the wheat grains. “Our studies have shown that a combined approach can optimize nutrient uptake, delivering both improved grain quality and reduced toxicity,” said a lead researcher at the UFZ.
How did it end (or what are the next steps)? The study concluded with a recommendation to shift towards combined or alternating fertilization strategies. Future research will focus on understanding how changing environmental conditions impact metal uptake and optimizing fertilization practices further.
