In a detailed review published in the journal Plants, authors Muhammad Umair Hassan and Qitao Su evaluate the multi-faceted role of biochar in addressing the global challenge of chromium pollution in agricultural soils. The researchers emphasize that chromium, particularly in its hexavalent form, is highly mobile and toxic, severely impairing plant development and posing a direct threat to food security. By consolidating findings from numerous industrial and agricultural trials, the study illustrates how biochar serves as a sustainable stabilization tool. The review underscores that biochar does not just improve soil quality but actively transforms the chemical state of pollutants to make them less dangerous to living organisms.

The findings reveal that biochar application can lead to a dramatic improvement in plant physiological resilience and physical growth metrics. Quantitative data from the study show that in chromium-polluted environments, biochar treatments can increase root 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 by as much as 99.7 percent and grain yield by 98.2 percent in crops such as maize. This recovery is largely attributed to the material’s ability to maintain high leaf water status and membrane integrity. For instance, biochar has been shown to increase relative water content by over 20 percent while simultaneously reducing electrolyte leakage, a key indicator of cell damage, by significant margins. These improvements allow plants to maintain normal metabolic functions even in the presence of high heavy metal concentrations.

A critical result of the research is biochar’s capacity to regulate the internal defense systems of plants through enhanced antioxidant activity. When exposed to chromium, plants typically suffer from oxidative stress, which destroys proteins and lipids. However, the study points out that biochar application boosts the activity of essential enzymes like superoxide dismutase and catalase by 23 to 50 percent. This biochemical support helps neutralize harmful reactive oxygen species before they can cause permanent damage. Furthermore, the researchers found that biochar reduces the accumulation of chromium in edible plant parts, such as spinach leaves, by 39 to 60 percent, directly lowering the health risks associated with consuming crops grown in contaminated areas.

The study also details the mechanisms by which biochar improves the biological health of the soil to counter metal toxicity. Biochar provides a stable habitat and carbon source for beneficial soil microbes, such as those from the Actinobacteria and Firmicutes groups, which are known for their metal-resistance properties. By promoting these resilient bacterial communities, biochar facilitates the natural enzymatic reduction of toxic hexavalent chromium into the less harmful trivalent form. The researchers observed that this restoration of microbial diversity leads to a significant increase in soil enzyme activities, such as a 29 percent rise in urease activity, which is vital for nutrient cycling. These biological changes create a self-sustaining environment that continues to lock away toxins over time.

Beyond immediate plant growth, the research highlights the importance of feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More selection and production temperature in determining biochar effectiveness. The review notes that biochar produced at specific temperatures possesses unique functional groups on its surface that act as electron donors, facilitating the chemical transformation of chromium. By neutralizing the structural similarities between chromium and essential nutrients like sulfate or phosphate, biochar prevents the toxic metal from competing for uptake. This selective immobilization ensures that plants can absorb the minerals they need for growth without taking in the pollutants. The researchers conclude that while biochar is not a universal cure, its strategic use offers a highly effective, eco-friendly method for remediating polluted lands and ensuring safer food production.

Source: Hassan, M. U., & Su, Q. (2026). A solution to chromium toxicity? Unlocking the multi-faceted role of biochar. Plants, 15(2), 234.