Bioavallabilily of organic contaminants may be ,0nfO\.Jnded by several
processes operating simultaneously in soil subsurtace. Model preoirtions 01 tare aod
transport o( organic contaminants in soils and groundwaler are sensitive to
assumptions conceminq rates of microbial degradation. In the current study, the
herbicide 2,4-0 was chosen as a model compound, since i1 is an aromatic chlorinated
molecule, whIch Is strvctu~lIy similar 10 numerous other compoundS of co/rent
interest The objective was to illustrale the impact of the inltlat soil environment
conditions on 2,4·0 bklavailabHity under batch and column transport conditions.
These condiUons tociude: moisture content, initial concentratlon, stlrroo reactor
versus stationary batch, biOmass, a&fObk versus anaerobic conoiuons. and pore
water veiocuv (I.e., residence time), Modeling 2,4-0 degradatlon with first-order
kinetics yieided poor predictions 01 de1)l1!datJon behavior and half, life In SOIl.
Accounting for bloavailabifity through the use 01 lha modified first-order and 1091slic
models presented more accurate predicUons of both the rate and e)((enl of 2,4·0
degradation. In the transport erwirorvnent, It Is no! dear whether microbial biomass
concentration responslble tot 2.4-0 degradallon rernaln constant under the tasted
range 01 pore water velocities, Apparent ~radaUon rate consiants rnav decrease
with increasing pore water velocity due to d€0e8sas in residence time per unit length
(thoughl of as IOCopportunity lime). In summary, the effects 01 residence time on
contamlnanr bloavailability may be confounded by several processes operating
simultane degradation and transport of organic contamtnants In SO~5 across a range o( flow
conditions using independenUy determined rate parameters.