Bioavailability — the Key Factor of Soil Bioremediation

Abstract

In the last two decades it has been shown that many pollutant compounds being found in soils or aqueous ecosystems may potentially be transformed by microorganisms. Transformation may be either completely into carbon dioxide and water, or at least into non-toxic metabolites (Klein 2000). These promising research results inspired many remediation companies to set up particular bioremediation approaches for the clean-up of such contaminated areas. The bio-enthusiasm of the early years, however, is now followed by a more realistic and sometimes even sceptical view of bioremediation. The major reason for this turn-around is that it has now become clear that results being obtained in the laboratory with artificially contaminated soils do not necessarily indicate what may happen actually in the field with soil from contaminated sites. With hydrophobic pollutants like PAH (Bossert et al. 1984; Erickson et al. 1993; Schaefer et al. 1995; Weissenfels et al. 1992) or some sorts of mineral oil (Angehrn et al. 1997; Bossert et al. 1984; Riis et al. 1998) in particular, it has been observed that even the degradation of compounds being completely mineralisable in the lab-culture may be incomplete in practical field bioremediation. Considerable residual concentrations of analytically detectable pollutants in the soil are subsequently left behind. An example for such a typical “hockey-stick-kinetic” (a term coined by M. Alexander, see Chapter 14) is shown in fig. 13.1.