Model polymer release system study of PAH bioaccessibility: the relationship between "rapid" release and...

This paper examines bacterial uptake of polycyclic aromatic hydrocarbons (PAHs) entrained within model polymer release systems (MPRSs) whose release kinetics, particularly for operationally defined "slow" release, are similarto PAH release kinetics from sediments and soils. We find that biodegradation is not restricted to the fraction "rapidly" released, f1, as quantified by an empirical biphasic exponential fitting parameter. Though our results indicate that f1 does not predict bioaccessibility (defined by a recent paper calling for a standard definition of same), we analyze the causes of the reported limitation of biodegradation to rapidly released PAHs and we find that, for the MPRSs, there are very strong correlations between an ad hoc bioaccessibility and a wide range of fitting parameters from various kinetic expressions used to phenomenologically characterize release. These results indicate that fitting parameters may be used to predict ad hoc bioaccessibility; however, it is not clear if this is actually a particularly useful quantity. We also report experimental results which indicate that bacteria may influence their environment and cause biological uptake to exceed that expected from abiotic release data obtained under quasi-infinite sink conditions. When this occurs, fitting parameters from simple empirical expressions are even inadequate to predict ad hoc bioaccessibility.