Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matrices

External and internal mass-transfer resistances influencing the bioavailabi lity of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite(R) adso rption resins (XAD4 and XAD7) were used as the synthetic model for soil agg regates. The effect of hydrodynamic conditions in the slurry phase on the d iffusive transport across a stagnant film surrounding the model particles w as studied. In addition, a mechanistic model was developed based on mass ba lances, diffusion equations, a nonlinear sorption isotherm, and microbial d egradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effe ctive diffusion coefficients of (3.55 +/- 0.10) x 10(-9) m(2)/s and (5.29 /- 0.86) x 10(-10) m(2)/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively.