Thermally enhanced bioremediation in tropical soil contaminated with naphthalene: a bioindicator-based perspective

Abstract Purpose The combination of bioremediation and thermal remediation techniques, known as thermally enhanced bioremediation, aims to efficiently remove soil contaminants. However, increasing the temperature in remediation processes can have negative impacts on soil microorganisms. Therefore, we aimed to evaluate the effects of soil heating and naphthalene contamination on soil quality and phytotoxicity variables. Materials and methods To simulate thermally enhanced bioremediation, soil samples were artificially contaminated with 5 naphthalene concentrations (0, 50, 100, 250 and 500 mg of naphthalene/kg of soil) and incubated at temperatures of 28, 38, 48 and 58 °C. The effects of the factors were determined using microbiological bioindicators (microbial activity and biomass, metabolic quotient and bacterial count on petri dishes), and phytotoxicity (germination and root length of lettuce seeds), assessed immediately and after 15 and 30 days of contamination. For statistical analysis of the bioindicators, multivariate analyses: PERMANOVA (Permutational Multivariate Analysis of Variance) and Principal Component Analysis were applied using software R. Results and discussion Based on the bioindicators applied, it was found that immediate contamination with naphthalene implied a reduction in biomass and microbial growth associated with greater environmental stress, due to increasing qCO2 values, at high concentrations (250 and 500 mg /kg). Over time (15 and 30 days), an interaction was identified between temperature and contaminant concentration, with a complex effect between these factors, the temperature range between 28 and 38 °C stimulated the growth of microbial communities, regardless of concentration. Conclusion In this study the results indicate that temperature ranges below 40 °C are promising for application in thermally enhanced bioremediation strategies, as they benefit soil microorganisms and potentially favor contaminant degradation.