In-situ phytoremediation of TNT-contaminated soil

Abstract

Parts of the area of the derelict World-War-II ordnance plant "Werk Tanne" (Clausthal-Zellerfeld, Harz, Germany) are heavily contaminated by chemicals resulting from TNT production and particularly by TNT itself. High soil contamination has to be treated with ex-situ methods but for the extended contamination of surface soil, in-situ phytoremediation is appropriate. The TNT-degrading potential of the rhizosphere of the planted trees and shrubs themselves is augmented by highly active mycorrhiza and white-rot fungi. A phytoremediation measure was established to scale with heavy machinery (soil grader), including the incorporation of white-rot fungi into the soil and planting of mycorrhized trees and shrubs. The effects of site preparation, mycorrhized rhizosphere and white-rot fungi on the degradation of TNT were assessed over one year using a complex monitoring scheme, including a battery of five biotests and field investigations of selected indicators (soil mesofauna, decomposition). The results of the monitoring showed the great influence of the grading procedure for site preparation, a diversified sensitivity of the biotest battery and complex reactions of the field indicators. The grading procedure effectively reduced the contamination (almost 90% within the first six months regardless of the initial levels). The phytoremediation measure as a whole reduced hazards of transport of nitro-aromatics by dust or leachate, initiated a secondary succession of the soil ecosystem that could transform the remaining TNT and metabolites over a longer period of time, and thus proved to be an effective decontamination measure applicable in large-scale technology.