Soil contamination with organic pollutants like pesticides, pharmaceuticals, and crude oil is a massive environmental problem. The FAO reports that 80% of agricultural soils contain such residues, contributing to a 15–20% loss in agricultural productivity. In a 2025 review in the journal Biochar , Nandita Das and Piyush Pandey explore an integrated, sustainable solution: biochar-driven rhizoremediation. This approach combines the natural detoxifying power of plant-microbe systems with the soil-enhancing benefits of biochar.

Rhizoremediation is an eco-friendly process that uses the synergistic interaction between plant roots and beneficial soil microbes to break down contaminants. The plant roots release root exudates—compounds like amino acids, organic acids, and proteins—which act as a food source for microbes, stimulating their activity and enhancing the degradation of pollutants nearby. However, this natural process is often slowed by factors like limited microbial activity and the poor bioavailability of pollutants in the soil.

This is where biochar acts as a catalyst, overcoming these limitations and accelerating cleanup. Biochar’s high porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More creates a protected, appropriate habitat for microorganisms, leading to a significant increase in the microbial population, which can be boosted up to 7.5log10 CFU g−1. Biochar is rich in key nutrients like potassium, magnesium, calcium, and phosphorus, which are essential for both plants and rhizospheric microbes. Its alkaline 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 and functional groups help mitigate soil acidity, fostering a more favorable environment for microbial growth. Biochar application has been shown to increase soil’s Cation Exchange Capacity (CEC) by up to 100% , and to reduce fertilizer requirements by 60%. Furthermore, biochar’s structure facilitates the adsorption and desorption of pollutants, initially reducing their toxicity to the plant while slowly releasing them to the microbes for degradation.

The combination of biochar and rhizoremediation has shown impressive results across different contaminant types. For Total Petroleum Hydrocarbons (TPH), studies incorporating biochar and rhizoremediation plants like ryegrass show TPH removal rates ranging from 47% to 76% , compared to 28–36% in the control treatment. One example using sugarcane bagasse biochar and Bacillus sp. showed 77% of the petroleum hydrocarbons were removed in maize-planted soil. Biochar significantly enhances the removal of Polycyclic Aromatic Hydrocarbons (PAHs). The combined use of biochar and ryegrass resulted in PAH removal rates of 49–51% in the biochar-rhizosphere zone, surpassing the 41–49% achieved by the rhizosphere alone. Furthermore, hardwood-derived biochar reduced the levels of accessible PAHs by more than 50%. For Pesticides, biochar applications reduced the plant absorption rates of carbofuran and chlorpyrifos by 25% and 10%, respectively. In addition, a bacterial consortium immobilized on biochar achieved a 96% degradation of metribuzin (MB), a stark contrast to the 29.3% observed in untreated soil. Finally, the rhizoremediation-biochar combination is highly effective against emerging contaminants like Antibiotics. Specifically, the use of Brassica juncea and Lolium multiflorum with biochar was able to remove 88.80–99.50% of sulfonamides and 28.00–92.89% of tetracycline.

To fully grasp the synergistic mechanism, researchers employ meta-omics approaches like metagenomics, transcriptomics, and metabolomics. Metagenomics analyzes the functional genes of microbial communities, revealing that biochar application altered the bacterial community, increasing α-diversity and the abundance of degrading bacteria like Pseudomonas and Zeaxanthinibacter. It also showed that biochar application restricted the transmission of antibiotic resistance genes (ARGs) from the rhizosphere to the root, leading to a 1.2–2.2% reduction in ARG abundance. Transcriptomics studies gene expression and shows that biochar upregulates genes related to biodegradation and nutrient cycling, thereby promoting soil health and degradation efficiency. For example, KEGG pathway analysis showed upregulation of key PAH degradation pathways. Lastly, Metabolomics examines cellular metabolites, showing that biochar and plant roots stimulate metabolic pathways like carbohydrate and lipid metabolism, which enhance bacterial resilience and accelerate contaminant elimination.

Source: Das, N., & Pandey, P. (2025). Biochar-driven rhizoremediation of soil contaminated with organic pollutants: engineered solutions, microbiome enrichment, and bioeconomic benefits for ecosystem restoration. Biochar, 7(1), 101.