What is the only effective treatment for removing organic contaminants from soils?

The correct answer is bioremediation. This method utilizes microorganisms to break down organic contaminants present in the soil into less harmful substances. The effectiveness of bioremediation stems from the natural processes of microbial metabolism, where bacteria, fungi, and other microorganisms consume the organic pollutants as a food source, thereby detoxifying and cleaning the soil.

Bioremediation can be enhanced through various techniques such as bioaugmentation (adding specific strains of microorganisms) or biostimulation (adding nutrients or oxygen to stimulate native microbial populations). This method is particularly advantageous because it can be cost-effective and environmentally friendly, promoting the natural degradation of contaminants rather than simply extracting or transferring the pollutants.

Other options, while effective in certain circumstances, do not solely focus on treating organic contaminants. Soil vapor extraction is effective for volatile organic compounds (VOCs) but is generally used in conjunction with other methods for broader contaminant types. Thermal desorption involves heating soil to evaporate contaminants, which can be effective but is energy-intensive and not always suitable for deeper contamination. Natural attenuation refers to the natural degradation processes that occur in the environment but relies on existing conditions and can take a long time, thus not guaranteeing effective remediation without supplemental action.