Inhibition of polycyclic aromatic hydrocarbon (PAHs) release from sediments in an integrated rice and crab coculture system by rice straw biochar

As persistent organic pollutants that are widely present in the environment and that pose substantial threats to human health, polycyclic aromatic hydrocarbons (PAHs) have received much attention from researchers around the world, but few studies have investigated the PAHs contamination of sediments in rice and crab coculture farming systems. In this study, rice straw biochar was prepared from rice straw, an abundant agricultural waste product, under oxygen-limited conditions at 500 °C. The rice straw biochar was characterized by scanning electron microscopy (SEM), specific surface and pore size analysis (BET), Fourier transform infrared spectroscopy (FTIR), and Raman Spectroscopy. The effect of using rice stalk biochar as a sorbent on the inhibition of the release and migration of PAHs from sediments in a rice and crab coculture system and the biological effects of PAHs within the system were studied for the first time. The results showed that rice straw biochar has a rich pore structure and high specific surface area, and the high-temperature charring method utilized in this study improved the charring and aromaticity of rice straw. The addition of rice straw biochar increased the immobilization of PAHs in sediments by 40.41%–119.62% and inhibited the migration of PAHs from the sediments to the overlying water, which reduced the PAHs content of the pore water at the sediment-water interface by 11.41%–58.73% and reduced the PAHs content of the overlying water in the dissolved and particulate forms by 54.67%–81.03% and 5.08%–55.20%, respectively. The addition of rice straw biochar reduced the biological effectiveness of PAHs in the system, and the enrichment of PAHs in crabs and rice decreased by 38.17–69.53% and 32.12%–97.63%, respectively. In addition, rice straw biochar changed the distribution of PAHs in rice, increasing the PAHs content of the stalks and leaves of rice by 2%–15% and 4%–17%, respectively, while the PAHs content of the roots was reduced by 8%–20%. These results confirm that rice straw biochar can effectively inhibit the migration and release of PAHs from sediments and reduce the bioavailability of phenanthrene (PHE) in integrated farming systems. The results provide theoretical and technical support for the study of straw waste utilization and remediation of PAHs pollution.