Resumo:
The combination of bioremediation and thermal remediation techniques, known as thermal bioremediation, aims to remove contaminants from the soil by stimulating microbial activity in the soil. However, increasing the temperature in remediation processes can have negative impacts on soil microorganisms, depending on the temperature range. Thus, we sought to evaluate the effects of soil heating and naphthalene contamination on microbiological variables of soil quality and phytotoxicity. To simulate thermal bioremediation, soil samples were artificially contaminated with five concentrations of naphthalene (0, 50, 100, 250, and 500 mg of naphthalene/kg of soil) and subjected, individually, to heating in ovens at temperatures of 28, 38, 48, and 58 °C. The effects of the factors were determined using microbiological variables – microbial activity and biomass, metabolic quotient, and bacterial count on plates – and phytotoxicity variables – germination and root length of lettuce seeds – evaluated immediately and after 15 and 30 days of contamination. For statistical analysis of the effects on the variables, R software was used, and multivariate analyses were applied: PERMANOVA (Permutational Multivariate Analysis of Variance), Hierarchical Cluster Analysis (HCA), Spearman's Correlation, Mantel's test, and Principal Component Analysis (PCA). In addition, the application of a methodology for the extraction and quantification of naphthalene was tested, the results of which were obtained successfully only for high concentrations, which made its application in monitoring naphthalene degradation unfeasible. Based on the variables applied, it was found that immediate naphthalene contamination led to a reduction in biomass and microbial growth, associated with greater environmental stress at high concentrations (250 and 500 mg/kg). Over time (15 and 30 days), an interaction between temperature and contaminant concentration was identified, with a complex effect between these factors; the temperature range between 28 and 38 °C stimulated the growth of microbial communities, regardless of concentration. These results indicate that temperature ranges below 40 °C are promising for application in thermal bioremediation strategies, as they benefit soil microorganisms and potentially favor contaminant degradation.
