Microorganisms that degrade heavy metals in agricultural soils

Biological solutions, such as the mycorrhizal-forming fungus Glomus iranicum var. tenuihypharum, reduce the cadmium concentration in the soil, preventing this heavy metal from being taken up by the plant and contaminating the fruit.


“More than 70% of the drylands used for agriculture in Latin America suffer from moderate to extreme degradation,” according to the United Nations Environment Program (UNEP). It also points out that increasing soil contamination threatens the “future of food production, human health, and the environment worldwide.”

One of the causes of the degradation of soil quality is the presence of heavy metals, such as cadmium, arsenic, lead, and mercury, which can also appear as residues in food as the result of agricultural fertilization and unsustainable soil management. The run-off containing heavy metals from agricultural soils affects river waters and water for human consumption.

Eighteen Latin American and Caribbean countries are working together to evaluate the effects of heavy metals in their soils through the RLA5089 project, which aims to generate knowledge and information about their environmental impact.

The consequences can be observed in the levels of heavy metals in agricultural products. At the beginning of last August, the European Commission’s Rapid Alert System for Food and Feed (RASFF) reported high cadmium levels in an avocado shipment from Peru that was sent to the Netherlands. This heavy metal was detected in Peruvian organic avocados for the fifth time this year.

Last July, the United States Food and Drug Administration (FDA) withdrew a shipment of organic blueberries from Lithuania, which had reported that the lead levels in these blueberry batches were above recommended levels.


Why are heavy metals found in crops?

“The primary soil structure rarely contains them,” stated Félix Fernández, Head of Technological Surveillance & Competitive Intelligence at Symborg. Most of the time, they are supplied through fertilization, primarily chemical synthesis fertilizers. “Phosphorous fertilizers contribute the most heavy metals because they are primarily associated with cadmium, arsenic, and zinc. For example, we need to make significant cadmium-contaminated contributions in volcanic soils, where there is no available phosphorous in the plant,” stated Félix.

In heavily worked soils in Latin America, especially in crops such as avocados and blueberries, heavy metals are a real problem. These soils lack available phosphorus and require significant applications of cadmium-contaminated fertilizer, which becomes a problem since the heavy metal does not easily degrade in the soil. In addition, the presence of cadmium in agricultural soils raises great concern due to the ease with which plants absorb it.


Biological solutions for controlling heavy metals

In Mexico, where the accumulation of heavy metals is a growing problem, especially due to the mining activity, phytoextraction is being used, which inoculates the plant with soil microorganisms, bacteria, and arbuscular mycorrhizal fungi, specifically fungi from the genus Glomus.

“One important microbial group that helps to degrade these metals is Glomus iranicum var. tenuihypharum.

Patented by Symborg, the symbiotic nature of this mycorrhizal-forming fungus absorbs the cadmium, encapsulating it in fat to prevent it from penetrating the plant. The small cadmium-containing fat droplets are excreted and later degraded by the soil microbiota,” Félix Fernández explained.

This microbial activity is crucial for controlling heavy metals in the soil and crop. A group of bacteria, primarily rhizopheric bacteria, have the metabolic capacity to degrade the cadmium-fat structure to reduce the concentrations of that heavy metal in the soil, finally preventing the cadmium from entering the plant and contaminating the fruit.

Our exclusive mycorrhiza-forming fungus, Glomus iranicum var. tenuihypharum, is present in our MycoUp, MycoUp 360, Resid MG and Resid HC biological inoculants.

This mycorrhizal-forming fungus prevents cadmium accumulation in the soil and its translocation to the fruit. “This has already been demonstrated in several studies with agribusinesses and universities in Peru, where the combined use of our MycoUp and MBB 10 products has been able to reduce the absorption of this metal by up to 90%”, stated Juan Luis Herrera, Business Sustainability Manager at Symborg Peru.

In the test performed on avocados by UNAS (National Agrarian University of the Jungle), a 40% reduction in cadmium levels was observed in the fruit compared to the control.

Three MycoUp applications were applied: one at a dose of 3 kg/ha, and the other two at a dose of 2 kg/ha each (August 15, October 23, and December 20), coinciding with flowering, olive-size fruit, and egg-size fruit phenologies.

As seen in the table below, the results show a clear decrease in cadmium levels in the fruit.


To conclude,  Glomus iranicum var. tenuihypharum not only improves soil quality but also increases nutrient absorption and efficient water use and improves the photosynthetic rate of the plant and root development. With good fertilization, irrigation and crop management, your agricultural production can be more profitable and much more sustainable over time.


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