Assessment of benzene, toluene, ethyl-benzene, and xylene (BTEX) toxicity in soil using sulfur-oxidizing bacterial (SOB) bioassay

The assessment of benzene, toluene, ethyl-benzene, and xylene (BTEX)-contaminated soil toxicity was performed using a sulfur-oxidizing bacteria (SOB) assay. The experiments were set up using an individual pollutant in a 25-mL bottle sealed with a rubber stopper and aluminum cap since BTEX are volatile. A large headspace volume (14 mL) was kept in the reactors to provide enough oxygen for the SOB. Soil samples were spiked with BTEX compounds in the concentration range of 1–1000 mg/kg. In reactors without BTEX compounds, approximately 85% of the theoretically required oxygen was consumed. Whereas, the reactors with benzene consumed in the range of 82–64% (5–100 mg/kg), those with toluene consumed 76–53% (1–50 mg/kg), those with ethyl-benzene consumed 44–71% (5–100 mg/kg), and those with xylene consumed 64–71% (1–10 mg/kg) of the theoretically required oxygen. The effective concentrations responsible for 50% growth inhibition (EC₅₀) for benzene, toluene, ethyl-benzene, and xylene detection were 130.2, 1.2, 15.2, and 0.7 mg/kg, respectively. These results suggest that this SOB-based bioassay can detect BTEX pollutants in soils.