Toxicity of Hydrocarbons to Microorganisms
Several classes of organic compounds are toxic for living organisms as they accumulate in and disrupt cell membranes. In these cases, the dose-dependent toxicity of a compound correlates with the logarithm of its partition coefficient between octanol and water (logP). Substances with a logP value between 1 and 5 are, in general, toxic for whole cells. Therefore, toxic effects of hydrocarbons on microorganisms can cause problems in bioremediation of highly contaminated sites. The toxic effect of most hydrocarbons is caused by general, nonspecific effects on membrane fluidity due to their accumulation in the lipid bilayer. Only exceptions are hydrocarbons with specific chemically active functional groups such as aldehydes and epoxides that show an additional chemical toxicity.
Most compounds with a higher hydrophobicity than logP of 4 such as e.g., alkanes, PAHs, and biphenyl(s) have very low water solubility, thus their bioavailability is too low to show a toxic effect. By combining the logP value with the water solubility of a compound the maximum membrane concentration (MMC) of a compound can be calculated. By using this parameter it is possible to predict the potential toxicity even of unknown hydrocarbons.