Cytogenetic and cytotoxic assessment of biochar derived from different feedstocks for agricultural biosafety evaluation

This study investigated the cytogenetic and cytotoxic effects of biochar (br) obtained from three plant residues such as maize stalks (MS), rice straw (RS), and tree residues (TR) on wheat ( Triticum aestivum L.) root tip cells. The br samples were physicochemical characterized, and their influence on seed germination, mitotic activity, and chromosomal behavior was assessed. Cytotoxicity was further evaluated using two human cell lines (Wi-38 and HBF4). The elemental composition varied markedly among the different br sources, leading to distinct biological effects. Maize stalk biochar (MSB), specifically at 3% and 6% concentrations, produced the highest mitotic index (MI) values and the lowest frequencies of chromosomal abnormalities, indicating minimum genotoxic stress. On the other hand, tree residue biochar (TRB) at comparable concentrations exhibited the lowest MI and the highest occurrence of chromosomal aberrations. Rice straw biochar (RSB) showed moderate effects, relatively stable mitotic activity and lower chromosomal irregularities at lower concentrations, compared to MSB and TRB. The observed abnormalities included chromosomal stickiness, lagging chromosomes, bridges, multi-nucleation, disturbed prophase and metaphase, distorted anaphase, elongated nuclei, and fragmented chromosomes. Cytotoxicity assays confirmed that TRB exerted the greatest inhibitory effects on both human cell lines, whereas MSB showed the least cytotoxicity, suggesting its relative safety for agricultural applications. This finding suggests that TRB could potentially have a different effect on soil characteristics and plant growth compared to the other two br types. These findings highlight the importance of biochar feedstock selection, as the source material profoundly influences its biological compatibility and relatively lower cytotoxic and genotoxic effects for environmental and agricultural use.