Enzymatic Activity and Its Relationship with Organic Matter Characterization and Ecotoxicity to Aliivibrio fischeri of Soil Samples Exposed to Tetrabutylphosphonium Bromide

This study aimed to determine the impact of tetrabutylphosphonium bromide [TBP][Br] on the soil environment through an experiment on loamy sand samples. The tested salt was added to soil samples at doses of 0 (control), 1, 10, 100, and 1000 mg kg−1 dry matter (DM). During the experiment, the activity of selected enzymes involved in carbon, phosphorus, and nitrogen cycles, characteristics of organic matter with Fourier-transform infrared (FT-IR) spectroscopy, and toxicity of soil samples in relation to Aliivibrio fischeri were determined at weekly intervals. The results showed that low doses of [TBP][Br] (1 and 10 mg kg−1 DM) did not have much influence on the analyzed parameters. However, the addition of higher doses of the salt into the soil samples (100 and 1000 mg kg−1 DM) resulted in a decrease in the activity of enzymes participating in the carbon and phosphorus cycle and affected the activation of those enzymes involved in the nitrogen cycle. This may be due to changes in aerobic conditions and in the qualitative and quantitative composition of soil microorganisms. It was also observed that the hydrophobicity of soil organic matter was increased. Moreover, the findings suggested that the soil samples containing the highest dose of [TBP][Br] (1000 mg kg−1 DM) can be characterized as acute environmental hazard based on their toxicity to Aliivibrio fischeri bacteria. The increased hydrophobicity and ecotoxicity of the soil samples exposed to the tested salt were also positively correlated with the activity of dehydrogenases, proteases, and nitrate reductase. Observed changes may indicate a disturbance of the soil ecochemical state caused by the presence of [TBP][Br].