Agricultural soils worldwide face a growing threat from heavy metal contamination, stemming from industrial activities, transport, and intensive use of agrochemicals. These pollutants, like cadmium, lead, and zinc, accumulate in soil, posing risks to both environmental safety and agricultural productivity by reducing fertility and potentially entering the food chain. Addressing this, a recent study published in Scientific Horizons by Nataliia Markova, Nataliia Nikonchuk, Svitlana Prystash, and Alla Bondar set out to evaluate the effectiveness of combining green manure with organo-mineral stabilizers, specifically zeolite and biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, to reduce heavy metal bioavailability and soil phytotoxicity. Their findings offer promising strategies for reclaiming degraded agricultural lands.

Heavy metals, such as cadmium, lead, zinc, and copper, do more than just alter soil properties; they significantly increase the risk of toxicants entering the food chain, posing a potential threat to human and animal health. Traditional remediation methods often prove expensive and energy-intensive. In this context, phytoremediationThis is a technique that uses plants to clean up contaminated soil or water. Biochar can enhance phytoremediation by improving soil conditions and promoting plant growth, allowing plants to absorb and break down pollutants more effectively.   More, which utilizes the biological potential of plants to reduce environmental pollution, is gaining traction as a greener alternative. However, the true efficacy of phytoremediation is determined not by the total metal content, but by its bioavailability—the portion accessible to plants and other organisms. This is where the strategic introduction of soil amendments plays a crucial role, converting mobile, toxic metal forms into more stable, less harmful ones.

The research, conducted on cadmium-contaminated southern chernozems in Ukraine, tested various stabilization methods. Zeolite emerged as a highly effective standalone solution, reducing available cadmium by a notable 58% and its total content by 22% compared to untreated control soils. This significant reduction is attributed to zeolite’s high cation exchange capacity, allowing it to bind and immobilize cadmium ions. Green manure alone also showed positive effects, decreasing cadmium bioavailability by 31%. However, the most compelling results were observed when biochar was combined with phytoremediation crops, such as sunflower and white mustard. This integrated approach reduced the availability of both cadmium and zinc by 50% in the soil solution. Critically, the overall removal of cadmium and zinc from the soil increased by 40% when biochar was used alongside phytoremediation compared to phytoremediation without biochar. This indicates a powerful synergistic effect, where biochar’s adsorptive capacity and its ability to improve growth conditions for plants lead to enhanced metal uptake.

Beyond simply reducing metal levels, these remediation strategies profoundly improved key soil physicochemical properties. The introduction of materials like limestone and zeolite raised the soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More from 5.6 to 6.8, shifting conditions where heavy metals tend to precipitate into less soluble forms. Green manure crops, such as white mustard and phacelia tansy, further boosted the soil’s health, increasing its organic carbon content by 18% and improving its cation exchange capacity by 11%. These changes enhance the soil’s ability to retain cations and form stable organo-metal complexes, which are less accessible to plants and reduce metal leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More by 30%.

The benefits extended directly to plant health and growth. Sunflower plants grown in biochar-treated plots exhibited a remarkable 24% increase in aboveground biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, reaching up to 35.2 grams per plant. Their photosynthetic activity also improved, with chlorophyll content increasing by 25%. Furthermore, markers of plant stress, like malonic dialaldehyde, decreased by 30% , while the activity of antioxidant enzymes—catalase and superoxide dismutase—increased by 32% and 41%, respectively. These physiological improvements signal a healthier plant response to contamination, indicating that the stabilizers effectively mitigate the toxic effects of heavy metals. Interestingly, cadmium accumulation in sunflower leaves and stems was 66% higher in biochar-treated variants (3.5 mg/kg dry weight) compared to non-biochar treatments (2.1 mg/kg), suggesting biochar not only stabilizes metals but also optimizes conditions for plants to actively absorb and translocate them for phytoremediation.

The study also highlighted the crucial role of microbial activity. Inoculation with rhizospheric bacteria, such as Pseudomonas fluorescens and Bacillus subtilis, increased heavy metal accumulation in plants by 20-30%. Similarly, mycorrhizal fungiThese are friendly fungi that form a partnership with plant roots. They act like an extension of the root system, helping plants access water and nutrients more effectively. Biochar can create a cozy habitat for these helpful fungi, boosting their growth and improving plant health.   More (Glomus intraradices) enhanced aboveground biomass by an average of 15%. These biological agents contribute to improved nutrient absorption and detoxification, strengthening the overall remediation effect. The close correlation (Pearson’s coefficient r=0.88) between the bioavailability of heavy metals in the soil and their accumulation in aboveground plant biomass further emphasizes that targeting bioavailability is key to predicting phytoremediation success and reducing environmental risk.

The practical implications of these findings are substantial. The combined use of zeolite (at 10 tons per hectare) and biochar (at 5 tons per hectare) with green manure and phytoremediation crops presents a multi-purpose agricultural practice. It offers environmental safety by reducing heavy metal mobility, economic feasibility through sustainable material use, and agronomic efficiency by improving soil health and plant growth. While the study was limited to one growing season and specific soil types, the results strongly advocate for adopting these integrated approaches in agriculture to safeguard soil resources and improve ecosystem functions in contaminated areas. Future research should explore long-term effects and the impact on microbial communities to fully understand the system’s stability.

Source: Markova, N., Nikonchuk, N., Prystash, S., & Bondar, A. (2025). Mechanisms for reducing heavy metal toxicity in fertiliser and agrotechnological soil protection systems. Scientific Horizons, 28(6), 89-99.