Earthworms, a means to accelerate removal of hydrocarbons (PAHs) from soil? A mini-review

Contamination of soil with hydrocarbons occurs frequently. Restoring contaminated soils is costly and time consuming. Earthworms accelerate the removal of hydrocarbons as they burrow through soil by rendering contaminants available for microbial degradation, by feeding on the organic matter that harbour contaminants, and by improving soil structure and aeration. Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant hydrocarbons that can contaminate the environment and can thus serve as models to study the factors that control the removal of petroleum from soil. The effect of earthworms on the removal of PAHs was reviewed. It was found that earthworms have the capacity to accelerate the removal of PAHs and their degradation products from soil. However, large numbers of earthworms are required, which might be expensive. Moreover, it may be difficult to provide sufficient organic material as feed while simultaneously maintaining high soil water content to allow burrowing.