Bioremediation of decabromodiphenyl ether or benzo(a)pyrene-contaminated rice-paddy soil

Purpose Polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons are common contaminants in soils. In PBDEs, decabromodiphenyl ether (BDE-209) is the most persistent, while benzo(a)pyrene (BaP) is an identified human carcinogen. This study is aimed to solve the contamination of BDE-209 and BaP in soils by adjusting environmental variables and amendments of microorganisms or nutrients. Methods A batch test and a sandbox test were performed. In the batch test on an artificial soil, the Taguchi method was applied to define optimum environmental factors. The sandbox test was conducted to verify if addition of soybean soil nanoemulsion (SONE) or acclimated microorganisms can assist the bioremediation of BDE-209 and BaP in rice-paddy soil under optimum volumetric water content (theta(W)). Next-generation sequencing (NGS) was performed to observe the microbial profile, correlation, and interaction. Results The batch test revealed that the theta(W) is the predominant factor for both contaminants. In the sandbox test, bioaugmentation with SONE-amended group achieved 55% and 74% removals in 70 days for fresh BDE-209 and BaP, respectively. Yet for weathered BDE-209, natural attenuation group was the best with about 75% removal in 70 days. NGS data showed that a few dominant genera formed a strong alliance against a large group of others. Conclusions The results suggest that the theta(W) is the key parameter and proper amendment of soil organic matter, and SONE can enhance the bioremediation. The results implied that natural attenuation with water flooding could be effective for the soils historically contaminated by BDE-209.