Mass Transfer Limitation of Biotransformation:  Quantifying Bioavailability

Abstract

Biotransformation is controlled by the biochemical activity of microorganisms and the mass transfer of a chemical to the microorganisms. A generic mathematical concept for bioavailability is presented taking both factors into account. The combined effect of mass transfer of a substance to the cell and the intrinsic activity of the cell using the substance as primary substrate, is quantified in a bioavailability number (Bn). The concept can easily be extended to secondary substrates. The approach has been applied to explain the observed kinetics of the biotransformation of organic compounds in soil slurries and in percolation columns. The model allowed us to predict threshold concentrations below which no biotransformation is possible. Depending on the environmental system and the chemical involved, predicted threshold concentrations span a range of 11 orders of magnitude from nanograms to grams per liter and match with published experimental data. Mass transferand not the intrinsic microbial activityis in most cases the critical factor in bioremediation.

Experimental Evaluation and Mathematical Modeling of Microbially Enhanced Tetrachloroethene (PCE) Dissolution

“…The bioavailability number (Bn) has been proposed for quantifying the relationship between the rate of dissolution and the rate of biotransformation (49): where a′ao (L -1 ) is the initial specific interfacial area of the DNAPL (interfacial area normalized by aqueous phase volume) and all other values are as described previously. Bn is a dimensionless parameter that arises during the derivation of the Best equation, which assumes the mass transfer flux and substrate degradation are approximately equal (quasisteady-state) (49). A Bn less than unity represents dissolutioncontrolled bioavailability, while a Bn greater than unity represents conditions where transformation is limited by the catalyst.…”

Evidence for in situ degradation of mono-and polyaromatic hydrocarbons in alluvial sediments based on microcosm experiments with 13C-labeled contaminants

“…This tendency is increasing with the number of their aromatic rings (Kleineidam et al, 2002;Kubicki, 2006). Sorption and poor solubility in water makes the major fraction of PAHs inaccessible for bacterial degradation (Bosma et al, 1997;Volkering et al, 1992). Although one controversial study reported on bacteria that directly accessed the sorbed substrate (Guerin and Boyd, 1997), presently it is believed that PAHs adsorbed on soil particles, solid PAH crystals, or hydrocarbons dissolved in non-aqueous phase liquids (NAPLs) remain unavailable to bacteria (Johnsen et al, 2005).…”

Use of a whole‐cell biosensor to assess the bioavailability enhancement of aromatic hydrocarbon compounds by nonionic surfactants

“…Even when microorganisms that can readily degrade HOCs are present, the compounds may not be accessible for assimilation by these organisms, or bioavailable, due to such factors as low aqueous solubility, strong binding and/or sequestration into soil organic matter and porous media matrices, and retarded rates of dissolution from nonaqueous phase liquids (NAPLs) (Bosma et al, 1997). Hence, the conventional hypothesis has been that microbial uptake of HOCs occurs only in the aqueous phase, and that compounds from a nonaqueous phase (e.g., NAPL, sorbed state, or micellar pseudophase) are made available only once they have partitioned to the aqueous phase (Ghoshal et al, 1996;Volkering et al, 1995;Weissenfels et al, 1992).…”