Chromium (Cr) contamination, largely from industrial wastewater and widespread in agricultural soils, poses a significant threat to crop safety and human health. Despite the known benefits of 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 in soil remediation, its application as a real-time filtration system in dynamic hydroponics has remained largely unexplored. A recent study by Yue et al., published in BMC Biotechnology, investigated the effectiveness of various biochar concentrations in alleviating Cr-induced stress in Chinese cabbage (Brassica rapa L.), a fast-growing and Cr-sensitive leafy vegetable. This research not only highlights biochar’s dual role in chromium adsorption and physiological stress reduction but also proposes an innovative strategy for protected agriculture.

The study utilized a flow-through hydroponic system to assess how different biochar concentrations (0.5, 1.25, and 2.5 g/L) could mitigate stress caused by 20 mg/L Cr (VI). The findings were remarkable. In the absence of biochar, chromium exposure significantly reduced plant 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, chlorophyll content, and antioxidant enzyme activity, while increasing oxidative stress markers and chromium accumulation in plant tissues. However, biochar treatments—particularly at the 2.5 g/L concentration—demonstrated significant improvements.

The physical and chemical properties of the biochar played a crucial role. Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis revealed a highly porous biochar structure, crucial for chromium adsorption. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of key functional groups like -OH and -COOH, which are essential for binding chromium. Furthermore, X-ray Photoelectron Spectroscopy (XPS) analysis verified successful chromium adsorption on the biochar surface and indicated a partial reduction of highly toxic Cr (VI) to the less toxic Cr (III) during the adsorption process, likely facilitated by redox-active oxygen-containing groups.

The impact on plant growth was substantial. The 2.5 g/L biochar treatment (BC3) significantly improved plant growth parameters. Shoot biomass increased by an impressive 322.48% compared to the chromium-stressed group without biochar. Root biomass also saw a substantial rise of 93.80%. Both shoot and root lengths improved, with shoots showing a 52.37% increase and roots a 13.14% increase with the optimal biochar dose. This highlights biochar’s ability to reduce chromium toxicity and improve nutrient availability, which are vital for plant vigor.

Biochar also effectively combated chromium accumulation within the plants. The BC3 treatment reduced chromium content in shoots by 98.03% and in roots by 98.04%, showcasing its remarkable efficiency in preventing heavy metal uptake. This reduction is attributed to the biochar’s porous structure and functional groups that bind to chromium ions, thus reducing their bioavailability to the plant.

Beyond growth and chromium reduction, biochar positively influenced the physiological health of the Chinese cabbage. Photosynthetic pigments, critical for plant growth, were significantly restored. Chlorophyll a increased by 84.46%, chlorophyll b by 4.67%, total chlorophyll by 53.52%, and carotenoids by 357.35% with the 2.5 g/L biochar treatment, demonstrating a strong recovery of photosynthetic capacity.

Moreover, biochar helped the plants mitigate oxidative stress. Soluble sugar content in shoots increased by 62.66% and in roots by 42.94% with the BC3 treatment, indicating improved metabolic balance. Soluble protein content in shoots also saw a significant increase of 147.80%. While chromium stress initially increased antioxidant enzyme activities like Superoxide Dismutase (SOD) and Peroxidase (POD) as the plant struggled to cope, higher biochar concentrations helped regulate these responses. For instance, in shoots, the BC3 treatment reduced SOD by 33.88% but boosted Catalase (CAT) by 303.79%, suggesting a more balanced and efficient antioxidant defense system. Furthermore, stress markers such as hydrogen peroxide (H2O2) and malondialdehyde (MDA) decreased significantly in both shoots and roots with biochar treatment, indicating reduced oxidative damage.

This study is a pioneering effort in demonstrating biochar’s effectiveness as a dynamic filtration medium for chromium remediation in hydroponic systems. The 2.5 g/L dose was identified as optimal, offering a practical and environmentally sustainable solution for managing heavy metal risks in hydroponic and urban agriculture, especially in resource-limited settings. This technology combines environmental and economic benefits, making it highly suitable for controlled agricultural production systems.

Source: Yue, S., Li, W., Qin, F., Dong, M., Weng, G., Ali, H. M., Weng, J., & Mehmood, S. (2025). Assessment of biochar filter application in improving chromium stress tolerance and plant physiology in Chinese cabbage (Brassica rapa) under a flow-through water setup. BMC Biotechnology, 25(74)