In situ vadose zone bioremediation.

Contamination of the vadose zone with various pollutants is a world-wide problem, and often technical or economic constraints impose remediation without excavation. In situ bioremediation in the vadose zone by bioventing has become a standard remediation technology for light spilled petroleum products. In this review, focus is given on new in situ bioremediation strategies in the vadose zone targeting a variety of other pollutants such as perchlorate, nitrate, uranium, chromium, halogenated solvents, explosives and pesticides. The techniques for biostimulation of either oxidative or reductive degradation pathways are presented, and biotransformations to immobile pollutants are discussed in cases of non-degradable pollutants. Furthermore, research on natural attenuation in the vadose zone is presented.