Multidimensional Toxicity of Rhamnolipid Extracts Obtained From Creosote‐Contaminated Soil

Abstract

In this study, a comprehensive research on the toxicity of rhamnolipids and their influence on the toxicity of water extracts obtained from creosote‐contaminated soil is performed. The obtained extracts contain organic compounds from the studied soil, which are eluted by pure water as well as solutions of rhamnolipids at different concentrations (ranging from 150 to 1500 mg L−1 where 150 mg L−1 corresponds with 1× critical micelle concentration (CMC). GC‐MS analyses allow for classification of the organic compounds into groups representing (i) 2‐ and 3‐ring polycyclic aromatic hydrocarbons (PAHs), (ii) 4‐ and 5‐ring PAHs, (iii) monoaromatic phenols, (iv) N‐heterocyclic compounds, and (v) other organic compounds. The addition of rhamnolipids reduces the elution of polar compounds and promoted the elution of hydrophobic compounds from soil (the elution of polycyclic hydrocarbons increases with increasing concentration of rhamnolipids). Moreover, HPLC‐MS analyses indicates a drop of the concentration of rhamnolipids compared to the initial concentration, suggesting a sorption of rhamnolipids on the soil matrix. Experiments regarding the toxicity toward activated sludge microorganisms (dehydrogenase activity assay), phytotoxicity (Phytotestkits), mutagenicity (Ames test), and cytotoxicity (MTT test) of extracts with and without rhamnolipids are also conducted. It is found that rhamnolipids increased the toxicity of the extracts toward microorganisms of activated sludge, phytotoxicity, cytotoxicity as well as mutagenicity toward Salmonella typhimurium TA 1537. The increasing toxicity in the presence of rhamnolipids can both be associated with increased bioavailability of toxic organic compounds as well as the toxicity of rhamnolipids.